int snprintf ( char * s, size_t n, const char * format, ... );
Write formatted output to sized buffer
Composes a string with the same text that would be printed if format was used on printf, but instead of being printed, the content is stored as a C string in the buffer pointed by s (taking n as the maximum buffer capacity to fill).

If the resulting string would be longer than n-1 characters, the remaining characters are discarded and not stored, but counted for the value returned by the function.

A terminating null character is automatically appended after the content written.

After the format parameter, the function expects at least as many additional arguments as needed for format.


Pointer to a buffer where the resulting C-string is stored.
The buffer should have a size of at least n characters.
Maximum number of bytes to be used in the buffer.
The generated string has a length of at most n-1, leaving space for the additional terminating null character.
size_t is an unsigned integral type.
C string that contains a format string that follows the same specifications as format in printf (see printf for details).
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n).
There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function.

Return Value

The number of characters that would have been written if n had been sufficiently large, not counting the terminating null character.
If an encoding error occurs, a negative number is returned.
Notice that only when this returned value is non-negative and less than n, the string has been completely written.



/* snprintf example */
#include <stdio.h>

int main ()
  char buffer [100];
  int cx;

  cx = snprintf ( buffer, 100, "The half of %d is %d", 60, 60/2 );

  if (cx>=0 && cx<100)      // check returned value

    snprintf ( buffer+cx, 100-cx, ", and the half of that is %d.", 60/2/2 );

  puts (buffer);

  return 0;


#include <stdio.h>

char buffer[200];
int i, j;
double fp;
char *s = "baltimore";
char c;

int main(void)
   c = 'l';
   i = 35;
   fp = 1.7320508;

   /* Format and print various data */
   j = snprintf(buffer, 6, "%s\n", s);
   j += snprintf(buffer+j, 6, "%c\n", c);
   j += snprintf(buffer+j, 6, "%d\n", i);
   j += snprintf(buffer+j, 6, "%f\n", fp);
   printf("string:%s character count = %d\n", buffer, j);