INFO: How C Interprets Integer Constants with Leading Zeroes

• 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, versions 1.0, 1.5, 1.51, 1.52
• Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

SYMPTOMS

Two similar assignment statements produce very different results when the application prints values assigned. For example:

   a = 20;
   printf("%d", a);   /* this prints "20" */
   a = 020;
   printf("%d", a);   /* but this prints "16" */

CAUSE

Any number with a leading "0" (zero) is interpreted to be an octal number (base 8).

RESOLUTION

Remove the leading zero from the decimal number.

MORE INFORMATION

All character constants of the form "\<o>", "\<o><o>", "\<o><o><o>", (where <o> is a digit) and their string equivalents are specified in octal as well. For example, \33 and \033 each specify the ESC character (decimal 27, hexadecimal 1B). To specify a character constant in hexadecimal, use "\x<h><h>", where <h> is a hexadecimal digit. C does not provide a method to specify a decimal number in a character constant; you can use a decimal integer constant instead (for example, ch = 27).

Keywords          : CLngIss
Version           : MS-DOS:6.00a,6.00ax,7.0; OS/2:6.0,6.00a;  WINDOWS:1.0,1.5,1.51,1.52; WINDOWS NT:1.0,2.0,2.1,4.0,5.0
Platform          : MS-DOS NT OS/2 WINDOWS
Issue type        : kbinfo