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The sprintf ("string print formatted") command is similar to asprintf, except that it is much less safe. Its first parameter is a string to which to send output. It terminates the string with a null character. It returns the number of characters stored in the string, not including the terminating null.

This function will behave unpredictably if the string to which it is printing overlaps any of its arguments. It is dangerous because the characters output to the string may overflow it. This problem cannot be solved with the field width modifier to the conversion specifier, because only the minimum field width can be specified with it. To avoid this problem, it is better to use asprintf, but there is a lot of C code that still uses sprintf, so it is important to know about it. (See asprintf.)

The following code example prints the string Being 4 is cool, but being free is best of all. to the string variable my_string then prints the string on the screen. Notice that my_string has been allocated 100 bytes of space, enough to contain the characters output to it. (See puts, for more information on the puts function.)

#include <stdio.h>

int main()
  char my_string[100];

  sprintf (my_string, "Being %d is cool, but being free is best of all.", 4);
  puts (my_string);

  return 0;