Q38296: How the Null Character Is Handled by Printf Functions.

Article: Q38296
Product(s): See article
Version(s): 4.00 5.00 5.10 | 4.00 5.00 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | S_QuickC | mspl13_c
Last Modified: 28-NOV-1988

When the C run-time functions printf, fprintf, or sprintf encounter
the character-conversion specifier %c in their format-control string,
they will convert the corresponding argument of int type to unsigned
char type and write the resulting value to output. Therefore, if the
argument is a NULL character, the value 0 (not the character "0") is
written to the output.

The output can be stdout, a file (with fprintf) or a string (with
sprintf). In case of stdout, the NULL character is ignored by the
display device. In the case of string, the NULL character will be
interpreted as a terminator character when the resulting string is
used later in the program.

The output of the following program is the result of expected
behavior:

#include <stdio.h>
char buffer[30] ;
main()
{
printf("Before,%c,After\n", '\0') ;
sprintf(buffer, "Before,%c,After\n", '\0') ;
printf(buffer) ;
}
/* end of sample program */

Output :

Before,,After
Before,

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