cprintfc-strings

Is it possible to print out only a certain section of a C-string, without making a separate substring?

Say I have the following:

char *string = "Hello, how are you?";

Is it possible to print out only the last 5 bytes of this string? What about the first 5 bytes only? Is there some variation of printf that would allow for this?

Solution

  • Is it possible to print out only the last 5 bytes of this string?

    Yes, just pass a pointer to the fifth-to-the-last character. You can determine this by string + strlen(string) - 5.

    What about the first 5 bytes only?

    Use a precision specifier: %.5s

    #include <stdio.h>
#include <string.h>
char* string = "Hello, how are you?";

int main() {
  /* print  at most the first five characters (safe to use on short strings) */
  printf("(%.5s)\n", string);

  /* print last five characters (dangerous on short strings) */
  printf("(%s)\n", string + strlen(string) - 5);

  int n = 3;
  /* print at most first three characters (safe) */
  printf("(%.*s)\n", n, string);

  /* print last three characters (dangerous on short strings) */
  printf("(%s)\n", string + strlen(string) - n);
  return 0;
}