MISRA C:2012 Rule 21.12

The standard header file <fenv.h> shall not be used

Description

Rule Definition

The standard header file <fenv.h> shall not be used¹ .

Rationale

In some cases, the values of the floating-point status flags are unspecified. Attempts to access them can cause undefined behavior.

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

Use of Features in <fenv.h>

#include <fenv.h>     /* Non-compliant */

void func(float x, float y) {
    float z;

    feclearexcept(FE_DIVBYZERO);              /* Non-compliant */ 
    z = x/y;

    if(fetestexcept (FE_DIVBYZERO))  {        /* Non-compliant */ 
    }
    else {
#pragma STDC FENV_ACCESS ON
        z=x*y;
        if(z>x) {
#pragma STDC FENV_ACCESS OFF
            if(fetestexcept (FE_OVERFLOW)) {  /* Non-compliant */ 
            }
        }
    }
}

In this example, the rule is violated when the identifiers feclearexcept and fetestexcept, and the macros FE_DIVBYZERO and FE_OVERFLOW are used.

Check Information

Group: Standard libraries

Category: Required

AGC Category: Required

Version History

Introduced in R2015b

R2025a: More functions and macros from <fenv.h> reported

Polyspace^® now reports the use of additional functions and macro from the header file <fenv.h>, including:

• FE_INEXACT

• FE_DIVBYZERO

• FE_UNDERFLOW

• FE_OVERFLOW

• FE_DFL_ENV

• FE_DOWNWARD

• FE_TONEAREST

• FE_TOWARDZERO

• FE_UPWARD

• fesetenv()

R2024a: Rule Categorized as Required

Following MISRA C:2012 Amendment 3, this rule is now categorized as Required.

R2024a: Including the header fenv.h reported as violation

Including the header fenv.h is now reported as a violation for this rule:

#include<fenv.h> //Noncompliant