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Each conversion specification is introduced by the % character followed (in order) by

• zero Zero or more flags (in any order), which modify the meaning of the conversion specification
• an An optional minimum field width
• an An optional precision that gives the minimum number of digits to appear for certain conversion specifiers
• an An optional length modifier that specifies the size of the argument
• a A conversion specifier character that indicates the type of conversion to be applied

Common mistakes in creating format strings include

• providing Providing insufficient arguments for the format string
• using Using invalid conversion specifiers
• using Using a flag character that is incompatible with the conversion specifier
• using Using a length modifier that is incompatible with the conversion specifier
• mismatching Mismatching the argument type and conversion specifier
• using Using an argument of type other than int for width or precision

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Legend:

• SPACE—the space (" ") character
• N/E—No —no effect
• NTBS—char* argument pointing to a null-terminated byte string
• NTWS—wchar_t* argument pointing to a null-terminated wide character string
• XSI—ISO/IEC 9945-2003 XSI extension

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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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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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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

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