MISRA C++:2023 Rule 30.0.1

The C Library input/output functions shall not be used

Since R2024b

Description

Rule Definition

The C Library input/output functions shall not be used. ¹

Rationale

Functions in <cstdio> such as gets(), fgetpos(), fopen(), ftell(), etc. have unspecified, undefined and implementation-defined behavior.

For instance:

• The gets() function has this use case:

  char * gets ( char * buf );

  The function does not check if the number of characters provided at the standard input exceeds the buffer buf. The function can have unexpected behavior when the input exceeds the buffer. Do not use the wide-character function equivalents in <cwchar>.

• The fopen function has implementation-specific behavior related to whether it sets errno on errors or whether it accepts additional characters following the standard mode specifiers.

Polyspace Implementation

Polyspace^® reports a violation of this rule if you use the functions declared in <cstdio> or the wide-character equivalents in <cwchar>. Polyspace detects the use of these <cstdio> functions:

• File operation functions such as remove() and rename().

• File access functions such as fclose(),fflush(), and fopen().

• Formatted input/output functions such as fprintf(), fscanf(), printf(), and scanf().

• Character input output functions such as fgetc(), fgets(), fputc(), and getc().

• Direct input/output functions such as fread() and fwrite().

• File positioning functions such as fgetpos() and fsetpos().

• Error handling functions such as clearerr(), ferror(), and perror().

Troubleshooting

If you expect a rule violation but Polyspace does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Use of fgets()

#include <cstdio>

void func()
{
    char array[10];
    fgets(array, sizeof array, stdin); //Noncompliant
}

The use of fgets() violates this rule.

Check Information

Group: Input/Output Library

Category: Required

Version History

Introduced in R2024b