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MISRA C:2012 Rule 21.20

The pointer returned by the Standard Library functions asctime, ctime, gmtime, localtime, localeconv, getenv, setlocale or strerror shall not be used following a subsequent call to the same function

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Description

Rule Definition

The pointer returned by the Standard Library functions asctime, ctime, gmtime, localtime, localeconv, getenv, setlocale or strerror shall not be used following a subsequent call to the same function.

This rule comes from MISRA C™: 2012 Amendment 1.

Rationale

The preceding functions return a pointer to an object within the Standard Library. Implementation for this object can use a static buffer that can be modified by a second call to the same function. Therefore the value accessed through a pointer before a subsequent call to the same function can change unexpectedly.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

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#include <stdio.h>
#include <locale.h>
#include <string.h>

void f1(void)
{
    const char* res1;
    const char* res2;
    char copy[ 128 ];
    res1 = setlocale(LC_ALL, 0);
    (void) strcpy(copy, res1);
    res2 = setlocale(LC_MONETARY, "French");
    printf("%s\n", res1);    /* Non-compliant */
    printf("%s\n", copy);    /* Compliant */
    printf("%s\n", res2);    /* Compliant */
}

In this example:

  • The first printf statement is non-compliant because the pointer returned by setlocale is used following a subsequent call to it when res2 is assigned.

  • The second printf statement is compliant because the copy operation performed by strcpy is made before a subsequent call to setlocale function is made.

  • The third printf statement is compliant because there is no subsequent call to the setlocale function is made before use.

Check Information

Group: Standard libraries
Category: Mandatory
AGC Category: Mandatory

Version History

Introduced in R2017a

See Also

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