Why Macro in C is So Notorious

In C programming language, macro is kind of notorious. Fortunately, we have alternative solutions in many cases. But there are still people who prefer macro as they may not aware of the risks of using macro. Therefore, I would like to list some in this post.

• Side effects

  If a expression passed to macros has side effects, the outcome might be unexpected:

  #define POWER(x) (x)(x)
  int i = 1;
  SQUARE(++i); // bug
  SQUARE(i++); // bug even subtle
  

  In C++, we may use either inline functions or templates instead.

  # inline function version
  inline int mySquare(const int i){return ii;}
  # template version
  template T mySquare(cosnt T& i){return ii;}
  

• Lack of grammar check

  In many implementations of stdio.h, getchar and putchar are defined macros. The error in the following code snippet is that putchar is provided with no parameter. But, can you tell that from compilation error message?

  /* test.c */
  #include <stdio.h> /* In stdio.h #define putchar(x) putc(x, stdout) */
  
  int main()
  {
      putchar ();
      return 0;
  }
  

  $ gcc test.c
  test.c: In function `main':
  test.c:5: error: parse error before ',' token
  
  $ gcc --version test.c
  gcc (GCC) 3.4.4 (cygming special) (gdc 0.12, using dmd 0.125)
  Copyright (C) 2004 Free Software Foundation, Inc.
  This is free software; see the source for copying conditions.  There is NO
  warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  

• Cannot single-step debug
• Cross-reference tools cannot handle/expand macros

namespace na
{
    #define NUM 1
}
namespace nb
{
    #define NUM 2
}