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Is there some way to detect the bad usage of bool values in code like
#include <stdbool.h>
void *foo(void)
{
return false;
}
int bar(void)
{
return true;
}
Both functions are accepted by gcc (8.3.1) and clang (7.0.1) without any warnings
$ gcc -Wall -W -pedantic -c x.c
$ clang -Xclang -analyzer-checker=alpha --analyze -Wall -W -pedantic -c x.c
$ clang -Wall -W -pedantic -c x.c
$
Compiling as C++ code would detect the problem in foo() but is not an option but rest of code is C, not C++.
Are there other (-W) options or switches which would create diagnostics for these cases?
599
This effectively reduces the compiler's ability to typecheck your program, since so many variables are pointers already, and C++ will happily stuff them into any bool argument to a function. It seems like the C99 _Bool type implements the same implicit type conversion brain damage.
In C99, bool is aliased to _Bool and if the flag is set, the above code will result in 'a' being 0x01 because of C99's requirements for type conversion. bool a = !! (someInt & 0x02) //'a' is now 0x01 when the bit is set.
This warning does not generally indicate that there is anything wrong with your code; it merely indicates that GCC’s optimizers are unable to handle the code effectively. Often, the problem is that your code is too big or too complex; GCC refuses to optimize programs when the optimization itself is likely to take inordinate amounts of time.
To help detect accidental misuses of such arrays GCC issues warnings unless it can prove that the use is safe. See Common Variable Attributes . Warn for cases where adding an attribute may be beneficial.
C defines the <stdbool.h> macros true and false as expanding to integer constant expressions of value 1 and 0 respectively. Since they're ints and bool (_Bool) in itself is an integer type, any such usage is equally valid. Even the value of the boolean expressions in C is an int and not a bool, so there is not much help for you with the bar function.
However, foo is a different beast - if the return value were true then it would be caught right away because 1 is not convertible to a pointer. false, having the integer constant value 0 is a null-pointer constant and will be converted to null pointer. You could perhaps catch the incorrect use by replacing the #include <stdbool.h> with something that does the inclusion but defines false as say 0.0 which is a falsy value but not an integer constant expression.
147
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