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Mismatches between arguments and conversion specifications may result in undefined behavior. Many compilers can diagnose type mismatches in formatted output function invocations.

const char *error_msg = "Resource not available to user.";
int error_type = 3;
/* ... */
printf("Error (type %s): %d\n", error_type, error_msg);

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This compliant solution ensures that the format arguments match their respective format specifications.

const char *error_msg = "Resource not available to user.";
int error_type = 3;
/* ... */
printf("Error (type %d): %s\n", error_type, error_msg);

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Passing them as any other type leads to undefined behavior. In this noncompliant code example, the width and precision are specified using parameters declared to be of size_t type. These are unsigned types that may not be the same size as int.

int print_int(int i, size_t width, size_t prec) {
  int n;

  n = printf("%*.*d", width, prec, i);

  return n;
}

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In this compliant solution, the field width and precision arguments to printf() format directives are of type int.

int print_int(int i, int width, int prec) {
  int n;

  n = printf("%*.*d", width, prec, i);

  return n;
}

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