INFO: Use of the Stringizing Operator (#) in Macros (57949)

SUMMARY

In Microsoft C for MS-DOS and Windows NT, when you are writing a preprocessor macro that takes an argument that must appear in quotation marks, you can use the # sign to expand the argument. One implementation of this preprocessor directive is the use of printf() in the macro. The following code demonstrates an example:

Sample Code

#define PR(fmt,value) printf("value = %" #fmt "\n", (value))

#include <stdio.h>

void main(void)
{
   float afl;

   afl = 3.14f;
   PR(5.2f, afl);
}
				

The sample code outputs the following string:

   value =  3.14
				

The # sign in front of the fmt variable allows the macro to be expanded using quotation marks. Note that the preprocessor concatenates consecutive pairs of double quotation marks so that the following string

   "value = %""5.2f""\n"
				

is translated into the following:

   "value = %5.2f\n"