Q43392: INFO: Clarification of the "g" Format Specifier for printf()

Article: Q43392
Product(s): Microsoft C Compiler
Version(s): MS-DOS:6.0,6.00a,6.00ax,7.00; OS/2:6.0,6.00a; WINDOWS:1.0,1.5; WINDOWS NT:1.0,2.0,4.0,5
Operating System(s): 
Keyword(s): kbcode kbCRT kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Last Modified: 22-JUL-2001

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The information in this article applies to:

- The C Run-Time (CRT), included with:
   - Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax 
   - Microsoft C for OS/2, versions 6.0, 6.0a 
   - Microsoft C/C++ for MS-DOS, version 7.0 
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5 
   - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 5.0, 6.0 
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SUMMARY
=======

In Microsoft C, the output format resulting from the printf() format specifier
"g" does not exactly match the output format resulting from either format
specifier "e" or "f". The documentation states that "g" will use either the "f"
or "e" format, whichever is more compact. This is true in the sense of the
overall format but there are some differences.

The precision value is interpreted differently in "g" format than in "f" format.
The documentation explains this difference. The precision for "f" specifies the
number of digits after the decimal point. The precision for "g" specifies the
maximum number of significant digits printed.

MORE INFORMATION
================

The following example demonstrates the difference described in the SUMMARY:

Sample Code
-----------

  #include <stdio.h>

  void main (void)
  {
     double x = 2.0/3.0; /* 0.666... */ 
     double y;

     y = 6.0 + x;
    printf ("%.4g\n", y);
    printf ("%.4f\n", y);
    printf ("%.4e\n\n", y);

     y = 66.0 + x;
    printf ("%.4g\n", y);
    printf ("%.4f\n", y);
    printf ("%.4e\n\n", y);

     y = 666.0 + x;
    printf ("%.4g\n", y);
    printf ("%.4f\n", y);
    printf ("%.4e\n\n", y);

     y = 6666.0 + x;
    printf ("%.4g\n", y);
    printf ("%.4f\n", y);
    printf ("%.4e\n\n", y);

     y = 66666.0 + x;
    printf ("%.4g\n", y);    /* switches to "e" notation here */ 
    printf ("%.4f\n", y);
    printf ("%.4e\n\n", y);
  }

The results of the above program are correct as shown below:

6.667
6.6667
6.6667e+000

66.67
66.6667
6.6667e+001

666.7
666.6667
6.6667e+002

6667
6666.6667
6.6667e+003

6.667e+004
66666.6667
6.6667e+004

Additional query words:

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Keywords          : kbcode kbCRT kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : MS-DOS:6.0,6.00a,6.00ax,7.00; OS/2:6.0,6.00a; WINDOWS:1.0,1.5; WINDOWS NT:1.0,2.0,4.0,5.0
Issue type        : kbinfo

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