# Standard library header <cfenv> (C++11)

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This header was originally in the C standard library as `<fenv.h>`.

This header is part of the floating-point environment library.

### Types

fenv_t (C++11) | the type representing the entire floating-point environment (typedef)
fexcept_t (C++11) | the type representing all floating-point status flags collectively (typedef)

### Functions

feclearexcept (C++11) | clears the specified floating-point status flags (function)
fetestexcept (C++11) | determines which of the specified floating-point status flags are set (function)
feraiseexcept (C++11) | raises the specified floating-point exceptions (function)
fegetexceptflagfesetexceptflag (C++11)(C++11) | copies the state of the specified floating-point status flags from or to the floating-point environment (function)
fegetroundfesetround (C++11)(C++11) | gets or sets rounding direction (function)
fegetenvfesetenv (C++11) | saves or restores the current floating-point environment (function)
feholdexcept (C++11) | saves the environment, clears all status flags and ignores all future errors (function)
feupdateenv (C++11) | restores the floating-point environment and raises the previously raised exceptions (function)

### Macros

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C++11) | floating-point exceptions (macro constant)
FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C++11) | floating-point rounding direction (macro constant)
FE_DFL_ENV (C++11) | default floating-point environment (macro constant)

### Synopsis

    #define FE_ALL_EXCEPT /* see description */
    #define FE_DIVBYZERO /* see description */    // optional
    #define FE_INEXACT /* see description */      // optional
    #define FE_INVALID /* see description */      // optional
    #define FE_OVERFLOW /* see description */     // optional
    #define FE_UNDERFLOW /* see description */    // optional

    #define FE_DOWNWARD /* see description */     // optional
    #define FE_TONEAREST /* see description */    // optional
    #define FE_TOWARDZERO /* see description */   // optional
    #define FE_UPWARD /* see description */       // optional

    #define FE_DFL_ENV /* see description */

    namespace std {
        // types
        using fenv_t    = /* object type */;
        using fexcept_t = /* object type */;

        // functions
        int feclearexcept(int except);
        int fegetexceptflag(fexcept_t* pflag, int except);
        int feraiseexcept(int except);
        int fesetexceptflag(const fexcept_t* pflag, int except);
        int fetestexcept(int except);
        int fegetround(void);
        int fesetround(int mode);
        int fegetenv(fenv_t* penv);
        int feholdexcept(fenv_t* penv);
        int fesetenv(const fenv_t* penv);
        int feupdateenv(const fenv_t* penv);
    }

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 3905 | C++11 | `std::fexcept_t` must be an integer type | it is an object type

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