[cfenv.syn]

# 29 Numerics library [[numerics]](./#numerics)

## 29.3 The floating-point environment [[cfenv]](cfenv#syn)

### 29.3.1 Header <cfenv> synopsis [cfenv.syn]

[🔗](#header:%3ccfenv%3e)

#define FE_ALL_EXCEPT *see below*#define FE_DIVBYZERO *see below* // optional#define FE_INEXACT *see below* // optional#define FE_INVALID *see below* // optional#define FE_OVERFLOW *see below* // optional#define FE_UNDERFLOW *see below* // optional#define FE_DOWNWARD *see below* // optional#define FE_TONEAREST *see below* // optional#define FE_TOWARDZERO *see below* // optional#define FE_UPWARD *see below* // optional#define FE_DFL_ENV *see below*namespace std {// typesusing fenv_t = *object type*; using fexcept_t = *object type*; // functionsint 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(); 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);}

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L138)

The contents and meaning of the header [<cfenv>](#header:%3ccfenv%3e "29.3.1 Header <cfenv> synopsis [cfenv.syn]") are a subset of the C standard library header [<fenv.h>](support.c.headers.general#header:%3cfenv.h%3e "17.15.1 General [support.c.headers.general]") and
only the declarations shown in the synopsis above are present[.](#1.sentence-1)

[*Note [1](#note-1)*:

This document does not require an implementation to support theFENV_ACCESS pragma;
it is implementation-defined ([[cpp.pragma]](cpp.pragma "15.10 Pragma directive"))
whether the pragma is supported[.](#1.sentence-2)

As a consequence,
it is implementation-defined
whether these functions can be used to test floating-point status flags,
set floating-point control modes, or run under non-default mode settings[.](#1.sentence-3)

If the pragma is used to enable control over the floating-point environment,
this document does not specify the effect on
floating-point evaluation in constant expressions[.](#1.sentence-4)

— *end note*]

See also: ISO/IEC 9899:2024, 7.6