c宏扩展错误

Question

Hi please find the below simple macro code

#include <iostream>

#define INCL    #include

INCL <stdlib.h>

int main()
{
    std::cout << "Hello, world\n" << std::endl ;

    return 0;
}

When I compile the code It throws error: stray â#â in program

Please help.

Thanks

Answer 1

Preprocessor macros cannot create other preprocessor macros. You're just out of luck in this regard.

However, you can use a macro as the include argument:

#define FOO(x) "/usr/lib/" #x
#include FOO(mylib.h)

Answer 2

C++ build consists of the following stages:

1. Preprocessing (macros expansion)
2. Compiling
3. Linking

The point is that you try to use preprocessor (stage 1) to preprocess itself, which won't work. The macros can only be used for generating the code for compiler. You cannot wrap a preprocessor directive into a preprocessor macro.