Continuing with the change to the STL, the text function of the Token class was also modified to build the string into a standard string stream. Like with the text function of the RPN List class, the with indexes option argument was not being utilized, so it was removed.
For the Token class, the return value of the text function was changed to a standard string. Callers were modified accordingly for this change. Only one caller remains that expects a QString value, the delete operator function. This function will not been needed once smart (shared) pointers are used for token pointers.
The way the private text operand helper function was used in the text function was changed making a separate function unnecessary. This helper function surrounded the token text with vertical bars and only two call located were left once the with indexes feature was removed. Instead of setting the second string, the string was changed to a flag and at the end of the function, if set, the vertical bars and the token string are added to the string stream.
[branch cpp11 commit 47766746a1]
Thursday, September 4, 2014
Wednesday, September 3, 2014
RPN Item – Index Member and Text Function
The next step will be to use smart pointers for RPN list pointers. In keeping with the change to STL classes, the RPN list will be changed from a QList to a std::list. Even though QList is like std::vector internally (an allocated array), a double linked list container is more appropriate because there is one instance so far (the INPUT command) where RPN items are inserted into the list. Inserting into an array requires moving all the elements from the insertion point.
While reviewing the code for these changes, it was noticed that the index member of the RPN item was only being used for test output. This index is set when an RPN item is appended to the list. If an item is inserted into the list, the index of every item after the inserted item needs to be incremented. This index is only output on attached items as a check to make sure the correct item is attached.
Current, attached RPN items always occur before the item that are attached to, which means the indexes could be assigned to an item as it is converted to text. Therefore the index of each item will be assigned and temporarily held in an unordered map (RPN item pointer to index) instead of assigning an index when the item is appended (and incremented later for inserts). The index was removed from the RPN Item class.
The text function of the RPN List class was modified to handle the conversion of each item to text using access functions of the RPN Item class so that the indexes can be added (from the temporary map) instead of calling the text function of the RPN item (which would not have the temporary indexes). Since the text function of the RPN Item class is no longer needed, it was removed. Also, the with indexes option argument was not being utilized and so this feature was also removed.
The text function was also modified to build the text of the RPN List into a standard string stream (std::stringstream, which works like an output stream but puts the result into a string). This is easier for building a string than using the standard string which is feature limited. For now, when the final standard string is obtained from the string steam, it is converted to a QString (since that it how the caller uses it, for now). Also, the text from the token needs to be converted from a QString to a standard string before adding to the string stream.
[branch cpp11 commit da4fcfbb23]
While reviewing the code for these changes, it was noticed that the index member of the RPN item was only being used for test output. This index is set when an RPN item is appended to the list. If an item is inserted into the list, the index of every item after the inserted item needs to be incremented. This index is only output on attached items as a check to make sure the correct item is attached.
Current, attached RPN items always occur before the item that are attached to, which means the indexes could be assigned to an item as it is converted to text. Therefore the index of each item will be assigned and temporarily held in an unordered map (RPN item pointer to index) instead of assigning an index when the item is appended (and incremented later for inserts). The index was removed from the RPN Item class.
The text function of the RPN List class was modified to handle the conversion of each item to text using access functions of the RPN Item class so that the indexes can be added (from the temporary map) instead of calling the text function of the RPN item (which would not have the temporary indexes). Since the text function of the RPN Item class is no longer needed, it was removed. Also, the with indexes option argument was not being utilized and so this feature was also removed.
The text function was also modified to build the text of the RPN List into a standard string stream (std::stringstream, which works like an output stream but puts the result into a string). This is easier for building a string than using the standard string which is feature limited. For now, when the final standard string is obtained from the string steam, it is converted to a QString (since that it how the caller uses it, for now). Also, the text from the token needs to be converted from a QString to a standard string before adding to the string stream.
[branch cpp11 commit da4fcfbb23]
Monday, September 1, 2014
RPN Item Pointers As Shared Pointers
An attempt was made to replace all the token pointers with a shared pointer class (QSharedPointer). A lot of changes were required that created many compile issues to correct. Worst, when running the first time, there were many crashes that were not being easy to resolve. I believe some of the problems were related to the RPN items (that hold token pointers) stored in the RPN output list. So, these changes were temporarily stashed.
Instead of starting with the token pointers, the simpler RPN item pointers were changed to use QSharedPointer. This was successful, however, I decided to try using the STL std::shared_ptr class (C++11 only) instead . After some testing, it appears that STL classes are faster than the equivalent Qt classes.
Originally, STL classes were avoided in favor of Qt classes, since this is a Qt based GUI application. With the recent desire to use C++11 and considering that the STL classes were enhanced and optimized to use C++11, STL classes will now be used as much as possible except when dealing specifically with GUI elements requiring Qt classes or when Qt classes have features not available in the STL classes (for example, the STL std::string class does not have a case insensitive comparison, but the QString class does).
To start the changes for the RPN item pointers, all instances of RpnItem* were changed to RpnItemPtr, which was defined as an alias (this using syntax is new to C++11 and is just an easier form of the typedef statement):
The RPN item constructor was changed to use the new initializer syntax instead of setting the member inside the constructor body. This is more efficient because otherwise, the default constructor is first called for each non-plain member and then a value is copied into the member. The RPN list class also no longer needed a clear function to delete the RPN items (the items get deleted automatically).
The attached array (with a count) in the RPN item class was naively implemented as a plain C array, which required naked new and delete operations and was changed to a QList. This change eliminates the need for a count variable (QList maintains its size) and also eliminates the need to delete the attached RPN items (automatic when the RPN item is deleted automatically).
When the RPN item pointer was changed to the STL std::shared_ptr class, the changes with QSharedPointer were put on a branch and the branch abandoned. The change in shared pointer class only required minor changes, which included changing the alias above and adding an alias for RPN item pointer vector:
[branch cpp11 commit a2069aae24]
[branch rpnitem-qt-sharedptr commit 7840954d5e]
Instead of starting with the token pointers, the simpler RPN item pointers were changed to use QSharedPointer. This was successful, however, I decided to try using the STL std::shared_ptr class (C++11 only) instead . After some testing, it appears that STL classes are faster than the equivalent Qt classes.
Originally, STL classes were avoided in favor of Qt classes, since this is a Qt based GUI application. With the recent desire to use C++11 and considering that the STL classes were enhanced and optimized to use C++11, STL classes will now be used as much as possible except when dealing specifically with GUI elements requiring Qt classes or when Qt classes have features not available in the STL classes (for example, the STL std::string class does not have a case insensitive comparison, but the QString class does).
To start the changes for the RPN item pointers, all instances of RpnItem* were changed to RpnItemPtr, which was defined as an alias (this using syntax is new to C++11 and is just an easier form of the typedef statement):
using RpnItemPtr = QSharePointer<RpnItem>;Many functions that had an RPN item pointer as an argument were changed to a reference to a RpnItemPtr so that the use count of the isn't unnecessarily incremented when a copy is made for the function call argument (and then decremented when the function returns). If the item is copied inside the function, the use count will get incremented. RPN items no longer need to be deleted as they now will be done automatically when they they go out of scope or their container is deleted or goes out of scope.
The RPN item constructor was changed to use the new initializer syntax instead of setting the member inside the constructor body. This is more efficient because otherwise, the default constructor is first called for each non-plain member and then a value is copied into the member. The RPN list class also no longer needed a clear function to delete the RPN items (the items get deleted automatically).
The attached array (with a count) in the RPN item class was naively implemented as a plain C array, which required naked new and delete operations and was changed to a QList. This change eliminates the need for a count variable (QList maintains its size) and also eliminates the need to delete the attached RPN items (automatic when the RPN item is deleted automatically).
When the RPN item pointer was changed to the STL std::shared_ptr class, the changes with QSharedPointer were put on a branch and the branch abandoned. The change in shared pointer class only required minor changes, which included changing the alias above and adding an alias for RPN item pointer vector:
using RpnItemPtr = std::shared_ptr<RpnItem>;The latter alias is used for the attached member (just changed to a QList) was changed to a std::vector (which is more similar to QList than to std::list as QList is an allocated array, std::list a double-linked list). Also, the size of STL classes is accessed using the size member function compared to the count member functions of the Qt classes.
using RpnItemPtrVector = std::vector<RpnItemPtr>;
[branch cpp11 commit a2069aae24]
[branch rpnitem-qt-sharedptr commit 7840954d5e]
Sunday, August 31, 2014
C++ Smart Pointers
C++ smart pointers are not a feature of the C++ language put a utilization of the language. Consider the function below, which is translation of the C way of handling allocated resources:
Fortunately, very elaborate smart pointer classes have already been implemented. In the C++11 version of the STL, there is the std::unique_ptr class, which is a more elaborate implementation of the class above. Qt has the similar QScopedPointer class.
The C++11 STL also has the std::shared_ptr class, which is a smart pointer that can be shared. These have a use count, which is incremented each time the pointer is copied (for example, put into a different list or stack). When one of the copies is deleted, the use count is decremented. When the use count reaches zero, the resource is automatically released. Qt has the similar QSharePointer class. These shared smart pointers will be used for the tokens, which get shared (in the RPN output list, done stack, holding stack, pending parentheses token, etc.).
bool function()Care must be taken to release the resources that were allocated to prevent memory leaks. This puts the burden on the programmer to make sure resources are released. Consider that if the class instances were local variables, their destructors would be called automatically when they go out of scope. This is the basic idea of a smart pointer, consider this simple smart pointer class:
{
Class *a {new Class};
// ... do some work ...
if (error)
{
delete a1;
return false;
}
Class *b {new Class};
// ... do some more work ...
if (error)
{
delete b;
delete a;
return false;
}
// ... do final work ...
delete b;
delete a;
return true;
}
class SmartPtrThe class holds the pointer to the allocated resource. When the smart pointer instance goes out of scope, its destructor will release the resource it is holding. The smart pointer provides access to the pointer it is holding. This class can be made more elaborate and convenient (for example, allowing the pointer to be replaced, allowing the pointer to be cleared, providing the indirection and arrow operators so that it behaves like a pointer, etc.), but this definition is sufficient to show the basic concept of smart pointers. The original function can be rewritten as:
{
Class *ptr; // hold pointer to allocated resources
public:
SmartPtr(Class *p) : ptr {p} {}
~SmartPtr() { delete ptr; }
const Class *pointer() const { return ptr; }
};
bool function()Note that it is no longer necessary to release the resources. The new calls in the first function are known as naked, each of which requires a corresponding naked delete. In the second function, the smart pointers hold the allocated resources (the new is enclosed). When the smart pointer goes out of scope, it destructor is called releasing the resource.
{
SmartPtr a {new Class};
// ... do some work ...
if (error)
{
return false;
}
SmartPtr b {new Class};
// ... do some more work ...
if (error)
{
return false;
}
// ... do final work ...
return true;
}
Fortunately, very elaborate smart pointer classes have already been implemented. In the C++11 version of the STL, there is the std::unique_ptr class, which is a more elaborate implementation of the class above. Qt has the similar QScopedPointer class.
The C++11 STL also has the std::shared_ptr class, which is a smart pointer that can be shared. These have a use count, which is incremented each time the pointer is copied (for example, put into a different list or stack). When one of the copies is deleted, the use count is decremented. When the use count reaches zero, the resource is automatically released. Qt has the similar QSharePointer class. These shared smart pointers will be used for the tokens, which get shared (in the RPN output list, done stack, holding stack, pending parentheses token, etc.).
Saturday, August 30, 2014
Memory Testing Issues
The next step is to start using C++ smart pointers (described in the next post). One use for smart pointers will be to replace the complicated code used to track the handling of tokens and the reporting of various errors (for example, memory leaks for tokens not freed). Smart pointers will make this code unnecessary. Before starting I thought it was a good idea to make sure the memory test scripts still worked.
There were no memory errors reported when using Qt 4.8.1 (installed with Mint13 or Ubuntu 12.04) or Qt 4.8.2 (installed with the kubuntu backports to get the latest KDE). However, when building the application with Qt 4.8.6 (the latest Qt 4.8 that was installed from source), memory errors were reported. The CMake build file was set up to generate the error suppression file from a template using the detected version and directory of Qt. This file was not tested with newer versions of Qt.
It appeared that with Qt 4.8.6, memory errors were reported differently (which was also the case with Qt 4.8.4, also built from source). After examining the output for each version of Qt, a common error suppressions file template was created that works with each of these four versions of Qt (other versions were not tested).
As with GDB, valgrind (the memory testing utility) only supports the new debug symbols output from GCC 4.8.1 starting with version 3.8.0 (3.7.0 is installed in Mint13). Version 3.9.0 is the latest available from source code. However, version 3.7.0 appears to work fine, including within Qt Creator. The new errors suppressions file also works with valgrind 3.9.0. Click Continue... for details on installing 3.9.0 from source, but this shouldn't be necessary on Mint 13 (Unbuntu 12.04). The valgrind 3.10.0.SVN installed on Mint 17 (Ubuntu 14.04) reports errors differently and does not work with this error suppression file (for now 3.9.0 would have to be installed from source).
[branch cpp11 commit a2069aae24]
There were no memory errors reported when using Qt 4.8.1 (installed with Mint13 or Ubuntu 12.04) or Qt 4.8.2 (installed with the kubuntu backports to get the latest KDE). However, when building the application with Qt 4.8.6 (the latest Qt 4.8 that was installed from source), memory errors were reported. The CMake build file was set up to generate the error suppression file from a template using the detected version and directory of Qt. This file was not tested with newer versions of Qt.
It appeared that with Qt 4.8.6, memory errors were reported differently (which was also the case with Qt 4.8.4, also built from source). After examining the output for each version of Qt, a common error suppressions file template was created that works with each of these four versions of Qt (other versions were not tested).
As with GDB, valgrind (the memory testing utility) only supports the new debug symbols output from GCC 4.8.1 starting with version 3.8.0 (3.7.0 is installed in Mint13). Version 3.9.0 is the latest available from source code. However, version 3.7.0 appears to work fine, including within Qt Creator. The new errors suppressions file also works with valgrind 3.9.0. Click Continue... for details on installing 3.9.0 from source, but this shouldn't be necessary on Mint 13 (Unbuntu 12.04). The valgrind 3.10.0.SVN installed on Mint 17 (Ubuntu 14.04) reports errors differently and does not work with this error suppression file (for now 3.9.0 would have to be installed from source).
[branch cpp11 commit a2069aae24]
Sunday, August 24, 2014
Qt Creator (GDB) No Watch Variables With GCC 4.8
The next set of changes are rather complicated and required debugging. Upon reaching the first breakpoint, no variables were displayed in the Locals and Expressions debugging window in Qt Creator. After a little research, the problem was determined to be with GCC 4.8.1, which is using a new format (named DWARF-4) to write debugging symbols to the executable.
The problem is that GDB (debugger) does not support this newer format, at least older versions prior to GDB 7.5. Mint 13 (Ubuntu 12.04) has only version 7.4. This problem does not affect Windows with the programs installed as recently described (see the Windows tagged posts). The latest MSYS with MinGW has GDB 7.6.1 and MinGW-w64 has GDB 7.7. Mint 17 (Ubuntu 14.04) is also fine with GDB 7.7.
There are two ways to solve this problem. The GCC compiler has an option for generating the older DWARF-3 format debugging symbols. Instead of permanently adding this option to the CMake build file, the following option can be added to the CMake command line or in Arguments field in the Run CMake wizard within Qt Creator:
The problem is that GDB (debugger) does not support this newer format, at least older versions prior to GDB 7.5. Mint 13 (Ubuntu 12.04) has only version 7.4. This problem does not affect Windows with the programs installed as recently described (see the Windows tagged posts). The latest MSYS with MinGW has GDB 7.6.1 and MinGW-w64 has GDB 7.7. Mint 17 (Ubuntu 14.04) is also fine with GDB 7.7.
There are two ways to solve this problem. The GCC compiler has an option for generating the older DWARF-3 format debugging symbols. Instead of permanently adding this option to the CMake build file, the following option can be added to the CMake command line or in Arguments field in the Run CMake wizard within Qt Creator:
-DCMAKE_CXX_FLAGS_DEBUG='-g -gdwarf-3'The other solution is to build and install GDB from source code. Click Continue... for details on the procedure for this.
Thursday, August 21, 2014
Token – Status As Enumeration Class
I misinterpreted how the compiler generates code for switch statements (caused by looking at disassembled output instead of assembler output of the compiler). The compiler does not generate an if-elseif chain in circumstances where it doesn't simplify a switch statement to an array of return values (when the return values are simple types as previously described).
The compiler still generates an array for a switch statement, but instead of an array of return values (of simple types), it generates an array of pointers. Each pointer is the address to the code for the case. During run-time, the processor indexes on the expression of the switch into this array and jumps to the address. While this is not space efficient, it is run-time efficient.
Unfortunately, for the token status enumeration, a single C style string constants cannot be used because each must be the result of the tr() translation function. This was not necessary for the other enumeration to string functions because these are only used for testing (translation is not necessary).
The switch statement for converting a token status enumerator was put into the message function of the Token class. This function previously returned an element from the static message array (which was removed). The status enumeration was put into the Token class as an enumeration class therefore requiring the Token::Status:: scoping prefix on the status enumerators. The _TokenStatus suffix was removed from each (the bug statuses did not have this prefix, but now require the scoping prefix).
The generation of the token status enumeration was removed from the auto-generation awk script and the token source file was removed as a dependency to the auto-generated enumerations header file. Several of the token status enumerators were not being used and were removed. The only auto-generated code remaining is for the code enumeration and the code enumerator to code name array. These will be handled later when the Table class is redesigned.
[branch cpp11 commit cfed68f09b]
The compiler still generates an array for a switch statement, but instead of an array of return values (of simple types), it generates an array of pointers. Each pointer is the address to the code for the case. During run-time, the processor indexes on the expression of the switch into this array and jumps to the address. While this is not space efficient, it is run-time efficient.
Unfortunately, for the token status enumeration, a single C style string constants cannot be used because each must be the result of the tr() translation function. This was not necessary for the other enumeration to string functions because these are only used for testing (translation is not necessary).
The switch statement for converting a token status enumerator was put into the message function of the Token class. This function previously returned an element from the static message array (which was removed). The status enumeration was put into the Token class as an enumeration class therefore requiring the Token::Status:: scoping prefix on the status enumerators. The _TokenStatus suffix was removed from each (the bug statuses did not have this prefix, but now require the scoping prefix).
The generation of the token status enumeration was removed from the auto-generation awk script and the token source file was removed as a dependency to the auto-generated enumerations header file. Several of the token status enumerators were not being used and were removed. The only auto-generated code remaining is for the code enumeration and the code enumerator to code name array. These will be handled later when the Table class is redesigned.
[branch cpp11 commit cfed68f09b]
Wednesday, August 20, 2014
Token – Type As Enumeration Class
A series of changes were made to change the token type enumeration to an enumeration class because its size of enumerator was used to dimension several arrays. The changes were put into several individual commits on a work branch, which were later combined (squashed using the interactive git rebase command) into a single commit and merged back to the cpp11 branch before pushing to GitHub. Details of these changes follow.
1) Unrelated to the token type enumeration, the Table class convert code function was moved to the Token class. This function contained arguments for a token with a data type and the desired data type to convert to. It returned a conversion code. However, it did not actually access the table. Since codes are not part of the table (the table is only indexed by codes) and this function took a token pointer, it made more sense for this to be a Token member function.
2) Also unrelated to the token type enumeration, the auto-generated data type to string map was changed to a brute force static function with a switch statement in the test source file as described in the previous post. (The compiler in-lined this function when set to release build.) The generate map function was removed from the test names awk script and the dependency on the main header file was removed from the auto-generated test names source file from the CMake build file.
3) Two of the uses of the token type enumerator was the static has parentheses flag and precedence arrays used to determine if the token type has a parentheses and the precedence of the token type. These arrays were initialized by the static initialize function. These arrays were changed to unordered maps with initializer lists for their values. Note that the maps do not contain values for all the token types. When the map is accessed for one of these other token types, a new element will be added with the correct default values (false for the flag, zero for the precedence). Since these maps are initialized, the initialize function was no longer needed and was removed.
4) The token type enumeration was changed to an enumeration class and was moved into the Token class where it belongs. Outside of the Token class, the token type enumerators need a double scope as in the Constant_TokenType enumerator becomes Token::Type::Constant.
5) The auto-generated token type to string array was changed to a brute force function also. (The compiler also in-lined this function.) The find enumeration function in the test names awk script was now no longer used and so was removed and the dependency on the token header file was removed from the auto-generated test names source file from the CMake build file.
[branch cpp11 commit e7dc6a964a]
1) Unrelated to the token type enumeration, the Table class convert code function was moved to the Token class. This function contained arguments for a token with a data type and the desired data type to convert to. It returned a conversion code. However, it did not actually access the table. Since codes are not part of the table (the table is only indexed by codes) and this function took a token pointer, it made more sense for this to be a Token member function.
2) Also unrelated to the token type enumeration, the auto-generated data type to string map was changed to a brute force static function with a switch statement in the test source file as described in the previous post. (The compiler in-lined this function when set to release build.) The generate map function was removed from the test names awk script and the dependency on the main header file was removed from the auto-generated test names source file from the CMake build file.
3) Two of the uses of the token type enumerator was the static has parentheses flag and precedence arrays used to determine if the token type has a parentheses and the precedence of the token type. These arrays were initialized by the static initialize function. These arrays were changed to unordered maps with initializer lists for their values. Note that the maps do not contain values for all the token types. When the map is accessed for one of these other token types, a new element will be added with the correct default values (false for the flag, zero for the precedence). Since these maps are initialized, the initialize function was no longer needed and was removed.
4) The token type enumeration was changed to an enumeration class and was moved into the Token class where it belongs. Outside of the Token class, the token type enumerators need a double scope as in the Constant_TokenType enumerator becomes Token::Type::Constant.
5) The auto-generated token type to string array was changed to a brute force function also. (The compiler also in-lined this function.) The find enumeration function in the test names awk script was now no longer used and so was removed and the dependency on the token header file was removed from the auto-generated test names source file from the CMake build file.
[branch cpp11 commit e7dc6a964a]
Tuesday, August 19, 2014
Better Enumerators To Strings Solution
Several enumerations need to be converted to strings for output during testing. This was accomplished with an awk script that scanned source files for the enumerations and automatically generated a source file that contained C style string arrays of the enumerator names, which were indexed by an enumerator. With enumeration classes, the enumerators can not be used as indexes to arrays. Another solution was to generate an unordered map that can be indexed by the enumerators provided that a generic hash is defined for enumeration classes.
The method of automatically generating source code from source code is kludgy and should be eliminated. Also, changing a source file read by an awk script forces the entire project to be rebuilt since all the source files are generally dependent on the auto-generated source file. A different solution was needed.
Another solution is using a function that takes an enumerator value as input and returns the string using the brute force method with switch statement and returning a string for each case, for example:
However, if the return type is QString and each return value is QString("Value1"), the compiler no longer generates an array, but instead an if-elseif chain. Though note that the actual return value can still be a C style string where the QString constructor is called to create the QString return value. (This information was acquired by looking at the assembly code generated.)
On the other hand, if the return value is a standard string (STL std::string), then the compiler does generate an array. This probably has something to do with the fact that the standard string class supports move constructors (a C++11 addition not discussed here). The QString class does not support these (at least Qt4 classes no not, but Qt5 classes do). The problem with using standard strings is that the return values of these functions are used with Qt stream classes, which do not support standard strings. Therefore, C style strings will be used for now.
Functions like the example above will be used. These functions could be auto-generated, but again this practice will no longer be used. The nice thing about auto-generation is that it eliminates the mistake of missing an enumerator, because with all warnings enabled (and as errors), if an enumerator is missing, a compiler warning is issued for the switch statement that not values are handled (provided no default case is included). This is not a perfect solution, but probably the best within the limits of the C++ language.
There is one final issue with the function above. The compiler sees that there is no return value at the end of the function and issues a warning (error). The compiler is apparently not smart enough to realize that execution does not get past the switch statement since all cases return. To silence this warning, a return ""; statement is needed at the end of the function.
The method of automatically generating source code from source code is kludgy and should be eliminated. Also, changing a source file read by an awk script forces the entire project to be rebuilt since all the source files are generally dependent on the auto-generated source file. A different solution was needed.
Another solution is using a function that takes an enumerator value as input and returns the string using the brute force method with switch statement and returning a string for each case, for example:
const char *enumName(Enum value)
{
switch (value)
{
case Enum::Value1:
return "Value1";
case Enum::Value2:
return "Value2":
...
case Enum::ValueN:
return "ValueN":
}
}
A good optimizing compiler will convert this switch statement to an array instead of a series of an if-elseif chain, which the GCC compiler does at the higher optimization levels. However, there are some conditions that are required. First, the compiler will only generate a look up array if the function is static (local to the source file where used). Also, the return values need to be relatively simply types.However, if the return type is QString and each return value is QString("Value1"), the compiler no longer generates an array, but instead an if-elseif chain. Though note that the actual return value can still be a C style string where the QString constructor is called to create the QString return value. (This information was acquired by looking at the assembly code generated.)
On the other hand, if the return value is a standard string (STL std::string), then the compiler does generate an array. This probably has something to do with the fact that the standard string class supports move constructors (a C++11 addition not discussed here). The QString class does not support these (at least Qt4 classes no not, but Qt5 classes do). The problem with using standard strings is that the return values of these functions are used with Qt stream classes, which do not support standard strings. Therefore, C style strings will be used for now.
Functions like the example above will be used. These functions could be auto-generated, but again this practice will no longer be used. The nice thing about auto-generation is that it eliminates the mistake of missing an enumerator, because with all warnings enabled (and as errors), if an enumerator is missing, a compiler warning is issued for the switch statement that not values are handled (provided no default case is included). This is not a perfect solution, but probably the best within the limits of the C++ language.
There is one final issue with the function above. The compiler sees that there is no return value at the end of the function and issues a warning (error). The compiler is apparently not smart enough to realize that execution does not get past the switch statement since all cases return. To silence this warning, a return ""; statement is needed at the end of the function.
Sunday, August 17, 2014
More Enumeration Classes
Several more enumerations were changed to enumeration classes. While more of these included a size of enumerator, they were not being used. This included the translator test mode, translator reference type, dictionary entry type, error list type, program model operation type, and the table multiple enumerations. Two instances where the enum keyword was in front of the enumeration name were removed (this is something required for C but not C++).
This leaves several enumerations that are not as easy as adding the class keyword and renaming the enumerators like those changed above. These include the code (auto-generated), token status (auto-generated), sub-code (bit masks), table flag (bit masks), table search type, token type, and test option enumerations.
The auto-generated enumerations need a good C++ solution and not the current kludgy C solution using an external awk script. The bit mask enumerations will need operator functions implemented (bit-wise OR and AND), which will require using type casting. For the others, the size of enumerators are used for either dimensioning arrays or for looping over the enumerators.
[branch cpp11 commit e71fe6f0fe]
This leaves several enumerations that are not as easy as adding the class keyword and renaming the enumerators like those changed above. These include the code (auto-generated), token status (auto-generated), sub-code (bit masks), table flag (bit masks), table search type, token type, and test option enumerations.
The auto-generated enumerations need a good C++ solution and not the current kludgy C solution using an external awk script. The bit mask enumerations will need operator functions implemented (bit-wise OR and AND), which will require using type casting. For the others, the size of enumerators are used for either dimensioning arrays or for looping over the enumerators.
[branch cpp11 commit e71fe6f0fe]
Data Type As Enumeration Class
Now that the number of and size of enumerators of the data type enumeration have been removed, there was one more enumerator left that needed to be removed if possible, specifically the No_DataType enumerator that was assigned to a -1, which was used to indicate an unset data type. If this enumerator was left in place, then switch statements would need to have a case for it or would need a blank default.
C++11 allows a default enumerator in the form EnumName{} just like for any other type. For user types, it calls the default constructor (if there is one, else a compile error is reported). For built in types, the value is assigned a zero. And so is the case for a default enumerator, which also has the equivalent value of zero. For unscoped enumerations, the value is zero, but for an enumeration class, the value can't be used as an integer without a cast.
Therefore, the No_DataType enumerator was replaced with the default enumerator DataType{}. In addition, the first enumerator can't have the default value of zero, so was assigned to the value of one. This is not an issue since data type enumerators are no longer used as indexes to array (only as keys to maps). All of the Xx_DataType enumerators were changed to just Xx in the class enumeration definition and to DataType::Xx for all uses in the code since the enumerators are now scoped.
There was one remaining issue. The test names awk script scanned the header file for the data type enumeration and created an array of C style strings with the names of the enumerator. As the string This awk script generates the test names header file used in the test source file for converting enumerators to strings for test output. The awk script was modified to instead look for the enumeration class and to generate an unordered map. This code was put into a new function in the script. This script also generates C style string arrays for the code and token type enumerations. These will also be changed at some point.
[branch cpp11 commit 06ef6f17c5]
C++11 allows a default enumerator in the form EnumName{} just like for any other type. For user types, it calls the default constructor (if there is one, else a compile error is reported). For built in types, the value is assigned a zero. And so is the case for a default enumerator, which also has the equivalent value of zero. For unscoped enumerations, the value is zero, but for an enumeration class, the value can't be used as an integer without a cast.
Therefore, the No_DataType enumerator was replaced with the default enumerator DataType{}. In addition, the first enumerator can't have the default value of zero, so was assigned to the value of one. This is not an issue since data type enumerators are no longer used as indexes to array (only as keys to maps). All of the Xx_DataType enumerators were changed to just Xx in the class enumeration definition and to DataType::Xx for all uses in the code since the enumerators are now scoped.
There was one remaining issue. The test names awk script scanned the header file for the data type enumeration and created an array of C style strings with the names of the enumerator. As the string This awk script generates the test names header file used in the test source file for converting enumerators to strings for test output. The awk script was modified to instead look for the enumeration class and to generate an unordered map. This code was put into a new function in the script. This script also generates C style string arrays for the code and token type enumerations. These will also be changed at some point.
[branch cpp11 commit 06ef6f17c5]
Size of Data Types Enumerator
The size of enumerator was removed but it was used for the dimension of two arrays. Both of these arrays were two dimensional, so some sort of compound map would have been needed. Instead, simple switch statements and conditional operators were used. This should be nearly as efficient as an array as the compiler may generate a lookup table for a switch and this is not in highly critical code so absolute efficiency is not required.
The first array was used to obtain a conversion code needed to convert the data type in a token to the desired data type. The conversion code obtained could be a null code representing no conversion needed or an invalid code representing a data type that can't be converted.
This array was used by the convert code and find code functions in the Table class. The convert code function was modified to process the two data types directly using compound switch statements (the first on the token data type, and the second on the needed data type). The find code function used the array for a data type in a token with the needed data type and so was changed to simply call the convert code function instead.
The second used of the size of enumerator was to dimension the an array used in the expected error status function of the Translator class. This array was dimensioned for the number of data types and the number of reference types (none, variable, variable or defined function, or all) and used to obtain a token error status when a reference is expected but not found. This function was changed to use a compound switch statement (the first on the data type, and the second on the reference type or the tertiary operator was used where a second switch was overkill). The size of enumerator for the reference enumerator was only used for this array and was also removed.
[branch cpp11 commit 4183a87f74]
The first array was used to obtain a conversion code needed to convert the data type in a token to the desired data type. The conversion code obtained could be a null code representing no conversion needed or an invalid code representing a data type that can't be converted.
This array was used by the convert code and find code functions in the Table class. The convert code function was modified to process the two data types directly using compound switch statements (the first on the token data type, and the second on the needed data type). The find code function used the array for a data type in a token with the needed data type and so was changed to simply call the convert code function instead.
The second used of the size of enumerator was to dimension the an array used in the expected error status function of the Translator class. This array was dimensioned for the number of data types and the number of reference types (none, variable, variable or defined function, or all) and used to obtain a token error status when a reference is expected but not found. This function was changed to use a compound switch statement (the first on the data type, and the second on the reference type or the tertiary operator was used where a second switch was overkill). The size of enumerator for the reference enumerator was only used for this array and was also removed.
[branch cpp11 commit 4183a87f74]
Saturday, August 16, 2014
Number of Data Types Enumerator
Not only does the data type enumerator have the size of enumerator (which needs to be removed before changing to an enumeration class), it also has a number of enumerator, which was placed after the three main data types (double, integer and string). This enumerator was removed, but is was used to dimension two arrays that needed to be changed.
In the Table constructor, there is a section that scans the secondary associated codes of a main code, the purpose of which is to set the expected data type for the main code. If the main code has associated codes for both doubles and integers, the expected data type is set to number (for example, the minus operator); and if there are associated codes for all three types (numbers and string), the expected data type is set to any (for example, the plus operator).
This is accomplished by using bit masks where there is a bit for each type (double, integer and string). For each associated code, the data type of the code is bit-wise ORed together. After all the associated codes are scanned, the final value is checked to see if it as the two number bits set or all three bits set to determine the expected data type.
Originally, an array of three elements was defined with the bit masks for the three data types. The number of enumerator was used to dimension this array. With the number of enumerator removed, this array was replaced with an unordered map, with an initializer list to set the bit masks for each data type enumerator.
The other use of the number of enumerator was in the equivalent data type function of the Table class, which contained an array from data type to equivalent data type, but when the sub-string and temporary string data types were removed, this function ended up essentially just returning the data type passed to it. In other words, this function is no longer does anything, so it was removed and the one use of it was replaced with the data type (in the LET translator routine).
[branch cpp11 commit 8f56e1117a]
In the Table constructor, there is a section that scans the secondary associated codes of a main code, the purpose of which is to set the expected data type for the main code. If the main code has associated codes for both doubles and integers, the expected data type is set to number (for example, the minus operator); and if there are associated codes for all three types (numbers and string), the expected data type is set to any (for example, the plus operator).
This is accomplished by using bit masks where there is a bit for each type (double, integer and string). For each associated code, the data type of the code is bit-wise ORed together. After all the associated codes are scanned, the final value is checked to see if it as the two number bits set or all three bits set to determine the expected data type.
Originally, an array of three elements was defined with the bit masks for the three data types. The number of enumerator was used to dimension this array. With the number of enumerator removed, this array was replaced with an unordered map, with an initializer list to set the bit masks for each data type enumerator.
The other use of the number of enumerator was in the equivalent data type function of the Table class, which contained an array from data type to equivalent data type, but when the sub-string and temporary string data types were removed, this function ended up essentially just returning the data type passed to it. In other words, this function is no longer does anything, so it was removed and the one use of it was replaced with the data type (in the LET translator routine).
[branch cpp11 commit 8f56e1117a]
Enumeration Class Hash
In order to use the STL unordered map class, a hash function is required for the key of the map. Hash functions are provided for all the built in types plus some of the other STL classes (like std::string), but unfortunately, not for enumeration classes. For the built in types (integers), the number itself is used as the hash. However, enumeration class enumerator values can't be because they can't be used as integers even though there values are just numbers. The solution is to use a generic (template) function type that will work for all enumeration classes that converts the enumerators to integers:
struct EnumClassHashThis works for any enumeration class by returning an integer for an enumerator (a size_t is an integer that is large enough to cover any enumeration) using a static cast (hopefully the only place a cast will be needed). An unordered map to use an enumeration class with an initializer list to assign values to the enumerators would be defined as:
{
template <typename T>
std::size_t operator()(T t) const
{
return static_cast<std::size_t>(t);
}
};
std::unordered_map<EnumName, QString, EnumClassHash> names {The name of the map does not need to be repeated for an assignment of each value (which could be tedious for a long name or with a lot of enumerators). This does not resolve the issue of forgotten values, but hopefully when an undefined enumerator value is accessed, the default value (in this case a blank string) would be detected or identified easily.
{First_EnumName, "First"},
{Second_EnumName, "Second"},
{Third_EnumName, "Third"}
};
QMap vs. Standard Map (Initializer Lists)
Using enumeration classes will require using an associated array container class (like QMap or QHash) since the size of the enumeration (the number of enumerators) is not obtainable (without kludgy type casting) to dimension an C style array. As mentioned in the previous post, to use a associated array container class requires run-time assignments to fill the container.
C++11 provides a solution with initialize lists. Unfortunately, the Qt containers do no support C++11 initializer lists (specifically Qt4 doesn't because Qt5 does contain support for initializer lists). The Standard Template Library (STL) containers does support initializer lists. Therefore, the STL containers will be used as needed until the inevitable change to Qt5. STL containers are technically already available since the various Qt containers have method functions for converting STL containers to and from Qt containers.
For an associated array, either the QMap or std::map container could be used. Both of these containers order the keys of the elements. Ordering of the keys is not required in this case. Qt provides the QHash class for an associated array not requiring ordered keys. Similarly, STL provides std::unordered_map, which will be the class used.
C++11 provides a solution with initialize lists. Unfortunately, the Qt containers do no support C++11 initializer lists (specifically Qt4 doesn't because Qt5 does contain support for initializer lists). The Standard Template Library (STL) containers does support initializer lists. Therefore, the STL containers will be used as needed until the inevitable change to Qt5. STL containers are technically already available since the various Qt containers have method functions for converting STL containers to and from Qt containers.
For an associated array, either the QMap or std::map container could be used. Both of these containers order the keys of the elements. Ordering of the keys is not required in this case. Qt provides the QHash class for an associated array not requiring ordered keys. Similarly, STL provides std::unordered_map, which will be the class used.
Enumerators As Indexes – Using A Map
The first enumeration that will be changed to an enumeration class will be the data type enumeration. One of the differences with enumerations is that unscoped enumerators can be used as integers. One of the other things I preferred to do when defining an enumeration was add a size of enumerator at the end:
Alternatively, using an associated array (map) instead of a C style array solves the issue of needing to know the size of the enumeration. Compare the array solution to the map solution:
The map method method of using assignments (same for the array method using assignments) can also be error-prone because it is easy to miss an assignment of one of the values. In the array case, a null pointer would be returned, which will probably cause a segmentation fault unless it is checked for.
For the map method, however, accessing a value that doesn't exist simply adds a new element to the map with a default value (in this case a blank string). This is still a problem, but much less fatal. Alternatively, in the case of QMap, the value method function could be used instead of the [] operator, which doesn't add an element for a non-existing element and allows a default value to be returned for the non-existing element (for example, in this case a default value like "BUG" could be used).
enum EnumName {This size of enumerator can then be used to dimension an array, like to hold a conversion to another value (another enumeration, string, etc.). This will not work with enumeration classes because the enumerators can't be used as integers without resorting to kludgy type casting (something I prefer to avoid if possible). Plus, once this size of enumerator is added, then any switch statement using the enumeration will generate a warning since there is no case statement for this enumerator. Adding a blank default statement is also kludgy.
First_EnumName,
Second_EnumName,
Third_EnumName,
sizeof_EnumName
};
Alternatively, using an associated array (map) instead of a C style array solves the issue of needing to know the size of the enumeration. Compare the array solution to the map solution:
QString names[sizeof_EnumName] = { QMap<EnumName, QString> names;The array method is error-prone and care must be taken to make sure the right values (strings in this case) are applied to the right elements in the array. This could be solved by using assignments that would look identical to the map assignments, though may not be as efficient because the assignments are done at run-time instead of at compile time, and the array still needs to be dimensioned.
"First", names[First_EnumName] = "First";
"Second", names[Second_EnumName] = "Second";
"Third" names[Third_EnumName] = "Third";
};
The map method method of using assignments (same for the array method using assignments) can also be error-prone because it is easy to miss an assignment of one of the values. In the array case, a null pointer would be returned, which will probably cause a segmentation fault unless it is checked for.
For the map method, however, accessing a value that doesn't exist simply adds a new element to the map with a default value (in this case a blank string). This is still a problem, but much less fatal. Alternatively, in the case of QMap, the value method function could be used instead of the [] operator, which doesn't add an element for a non-existing element and allows a default value to be returned for the non-existing element (for example, in this case a default value like "BUG" could be used).
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