C in a Nutshell

Name

snprintf

Synopsis

Stores formatted output in a string buffer

#include <stdio.h>
intsnprintf( char * restrict dest, size_t n,
              const char * restrict format, ... );

The snprintf() function is similar to printf(), but writes its output as a string in the buffer referenced by the first pointer argument, dest, rather than to stdout. Furthermore, the second argument, n, specifies the maximum number of characters that snprintf() may write to the buffer, including the terminating null character. If n is too small to accommodate the complete output string, then snprintf() writes only the first n -1 characters of the output, followed by a null character, and discards the rest. The return value is the number of characters (not counting the terminating null character) that would have been written if n had been large enough. To obtain the length of the output string without generating it, you can set n equal to zero; in this case, sprintf() writes nothing to dest, which may be a null pointer.

Tip

If the output overlaps with any argument that snprintf() copies data from, the behavior is undefined.

Example

char buffer[80];
double x = 1234.5, y = 678.9, z = -753.1, a = x * y + z;
int output_len = 0;

output_len =snprintf( buffer, 80, "For the input values %lf, %lf,"
                       " and %lf, the result was %lf.\n",
                       x, y, z, a );
puts( buffer );
if ( output_len >= 80 )
  fprintf( stderr, "Output string truncated! Lost %d characters.\n",
           output_len − 79 );

This code produces the following output:

For the input values 1234.500000, ...