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

• 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

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);
} 

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:

Keywords : kbcode kbCRT kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
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
Platform : MS-DOS NT OS/2 WINDOWS
Issue type : kbinfo