Q57961: Why External References Are Created When They’re Not Needed

Article: Q57961
Product(s): See article
Version(s): 5.00 5.10 | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 15-MAY-1990

Problem:

In the following example, Microsoft C compiler versions 5.00 and 5.10
generate an extern reference to printf(); therefore, the function is
included at link time. This apparently is a bug since the compiler
correctly ignores generating any code for the "if" statement.

The following is code example:

#define VERBOSE 0

int  function(void)
{
  if (VERBOSE) printf("hello world\n");

  return 1;
}

Response:

The way it works now is by design. The extern reference is generated
in the first pass of the compiler and the "if" code is removed in pass
two. Furthermore, according to ANSI specifications (Section 3.7,
"External Definitions" in December 7, 1988 draft), the extern is
required.

If your purpose is to provide conditional code for debugging reasons,
the preprocessor is much better suited to the task.

The above code fragment should be changed to the following:

#define VERBOSE 0

int  function(void)
{
#if (VERBOSE)
  printf("hello world\n");
#endif

  return 1;
}

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