FECLEAREXCEPT(3) | Library Functions Manual | FECLEAREXCEPT(3)

# NAME

`feclearexcept`, `fegetexceptflag`, `feraiseexcept`, `fesetexceptflag`, `fetestexcept` — access floating-point status flags

# SYNOPSIS

Math Library (libm, -lm)
`#include <fenv.h>`

int
`feclearexcept`(int excepts);

int
`fegetexceptflag`(fexcept_t *flagp, int excepts);

int
`feraiseexcept`(int excepts);

int
`fesetexceptflag`(const fexcept_t *flagp, int excepts);

int
`fetestexcept`(int excepts);

# DESCRIPTION

These functions provide access to the floating-point status flags. The excepts input argument is a bitmask specifying an exception type and containing any of the values listed below.

`FE_DIVBYZERO`
  A divide-by-zero exception occurs when the program attempts to divide a finite non-zero number by zero.
`FE_INEXACT`
  An inexact exception is raised whenever there is a loss of precision due to rounding.
`FE_INVALID`
  Invalid operation exceptions occur when a program attempts to perform calculations for which there is no reasonable representable answer.

  For instance, subtraction of infinities, division of zero by zero, ordered comparison involving NaNs, and taking the square root of a negative number are all invalid operations.

`FE_OVERFLOW`
  An overflow exception occurs when the magnitude of the result of a computation is too large to fit in the destination type.
`FE_UNDERFLOW`
  Underflow occurs when the result of a computation is too close to zero to be represented as a non-zero value in the destination type.
`FE_DENORMAL`
  Denormalization exception occurs when the result of a floating-point expression is a denormalized number.

  This is available only on the floating-point implementations of amd64 and i386 processors.

Additionally, the macro `FE_ALL_EXCEPT` is simply the bitwise OR of all floating-point exception macros listed above.

The `feclearexcept`() function clears the floating-point exceptions represented by excepts.

The `fegetexceptflag`() function stores a representation of the states of the floating-point flags indicated by excepts in the object pointed to by flagp.

The `feraiseexcept`() function raises floating-point exceptions represented by excepts.

The `fesetexceptflag`() function sets the floating-point status flags indicated by excepts to the states stored in the object pointed to by flagp. The value of flagp shall have been set by a previous call to `fegetexceptflag`() whose second argument represented at least those floating-point exceptions represented by excepts. This function does not raise floating-point exceptions, but only sets the state of the flags.

The `fetestexcept`() function determines which of a specified subset of the floating-point exception flags are currently set. The excepts specifies the floating-point status flags to be queried.

# RETURN VALUES

The `feclearexcept`(), `fegetexceptflag`(), `feraiseexcept`(), and `fesetexceptflag`() functions return zero on success, and non-zero if an error occurred. The `fetestexcept`() function returns a bitmask of a specified subset of the floating-point exception flags which are currently set.

# SEE ALSO

feenableexcept(3), fegetenv(3), fegetround(3)

# STANDARDS

The `feclearexcept`(), `fegetexceptflag`(), `feraiseexcept`(), `fesetexceptflag`(), and `fetestexcept`() functions conform to ISO/IEC 9899:1999 (“ISO C99”).

The return types for `feclearexcept`(), `fegetexceptflag`(), `feraiseexcept`(), and `fesetexceptflag`() are int for alignment with ISO/IEC 9899:1999 (“ISO C99”) Defect Report #202.

# HISTORY

These functions first appeared in OpenBSD 5.0.

# CAVEATS

On some architectures, `feraiseexcept`() additionally raises the “inexact” floating-point exception whenever it raises the “overflow” or “underflow” floating-point exception.

June 7, 2025 | Debian