Q57949: INFO: Use of the Stringizing Operator (#) in Macros

Article: Q57949
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Last Modified: 12-DEC-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 1.0, 1.5, 2.0, 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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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"

Additional query words: pound number

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Keywords          : kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbvc150 kbvc100 kbVC500 kbVC600 kbVC200 kbVC32bitSearch kbVC500Search
Version           : :1.0,1.5,2.0,4.0,5.0,6.0
Issue type        : kbinfo

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