I wish to replace a function call with a string using pre-processor directives. Something like this:
#ifdef DEBUG
#define Func1(arg) "Function not supported"
#endif
So basically when someone calls this function, I want a compilation error, such that this function is invisible in DEBUG mode, and in place of that , the following string is printed in the compilation log.
This method throws error.
Is there any other means to print a particular string i want when func1() is called?
The most obvious way to archieve such behaviour is to use #error directive. However since it's not possible to construct "conditional #error directive" I guess next move is _Pragma operator introduced in C99. Here is the solution that produces a message during compilation:
#include <stdio.h>
#define DEBUG 1
#ifdef DEBUG
#define Func1(arg) _Pragma("message \"Function not supported.\"")
#endif
void (Func1)(int arg)
{
}
int main(void)
{
Func1(1);
Func1(2);
Func1(3);
return 0;
}
Compilation (with gcc):
...
check.c:15: note: #pragma message: Function not supported.
check.c:16: note: #pragma message: Function not supported.
check.c:17: note: #pragma message: Function not supported.
I know It's not direct solution (such message is not even treated as warning, so -Werror doesn't change anything), however you can use e.g. grep tool or any other method to scan compiler's output.
Since GCC 4.8 there is also #pragma GCC error "message", which is direct (but non-portable) solution. Check this answer for more information. For example:
#ifdef DEBUG
#define Func1(arg) _Pragma("GCC error \"Function not supported.\"")
#endif
Func1(arg) function-like macro is "executed" is Func1(1); instruction in main definition. This doesn't matter that macro is defined, without proper invocation it doesn't do anything.One way is to simply leave the function undefined. This will result in an error at link time.
If you use gcc, you could use one of its extensions, a function attribute:
#ifndef DEBUG
#define __nodebugonly
#else
#define __nodebugonly __attribute__((error("Function not supported")))
#endif
void Func1(int arg) __nodebugonly;
__debugonly would be a misnomer then I changed that, too.You can use
#error "Function not supported"
to abort the compilation. But obviously when someone has access to the source that can be removed - so what exactly do you try to do?
If you don't trust those people with your source then don't give it to them. Link it into an .obj, define the 'interface' with a .h and only give out that.
