feclearexcept, fegetexceptflag, feraiseexcept, fesetex
ceptflag, fetestexcept, fegetenv, fegetround, feholdex
cept, fesetround, fesetenv, feupdateenv - C99 floating
point rounding and exception handling
void feclearexcept(int excepts);
void fegetexceptflag(fexcept_t *flagp, int excepts);
void feraiseexcept(int excepts);
void fesetexceptflag(const fexcept_t *flagp, int excepts);
int fetestexcept(int excepts);
int fesetround(int rounding_mode);
void fegetenv(fenv_t *envp);
int feholdexcept(fenv_t *envp);
void fesetenv(const fenv_t *envp);
void feupdateenv(const fenv_t *envp);
These eleven functions were defined in C99, and describe
the handling of floating point rounding and exceptions
(overflow, zero-divide etc.).
Exceptions are represented in two ways: as a single bit
(exception present/absent), and these bits correspond in
some implementation-defined way with bit positions in an
integer, and also as an opaque structure that may contain
more information about the exception (perhaps the code
address where it occurred).
Each of the macros FE_DIVBYZERO, FE_INEXACT, FE_INVALID,
FE_OVERFLOW, FE_UNDERFLOW is defined when the implementa
tion supports handling of the corresponding exception, and
if so then define the corresponding bit(s), so that one
can call exception handling functions e.g. using the inte
ger argument FE_OVERFLOW|FE_UNDERFLOW. Other exceptions
may be supported. The macro FE_ALL_EXCEPT is the bitwise
OR of all bits corresponding to supported exceptions.
The feclearexcept function clears the supported exceptions
represented by the bits in its argument.
The fegetexceptflag function stores a representation of
the exception flags represented by the argument excepts in
the opaque object pointed to by flagp.
The feraiseexcept function raises the supported exceptions
the exceptions represented by excepts to the value pointed
to by flagp. This value must have been obtained by an
earlier call of fegetexceptflag with a last argument that
contained all bits in excepts.
The fetestexcept function returns a word in which the bits
are set that were set in the argument excepts and for
which the corresponding exception is currently set.
Each of the macros FE_DOWNWARD, FE_TONEAREST,
FE_TOWARDZERO, FE_UPWARD is defined when the implementa
tion supports getting and setting the corresponding round
The fegetround function returns the macro corresponding to
the current rounding mode.
The fesetround function sets the rounding mode as speci
fied by its argument and returns zero when it was success
Floating point environment
The entire floating point environment, including control
modes and status flags, can be handled as one opaque
object, of type fenv_t . The default environment is
denoted by FE_DFL_ENV (of type const fenv_t *).
The fegetenv function saves the current floating point
environment in the object pointed to by envp.
The feholdexcept function does the same, then clears all
exception flags, and sets a non-stop (continue on excep
tions) mode, if available. It returns zero when success
The fesetenv function restores the floating point environ
ment from the object pointed to by envp. This object must
be known to be valid, e.g., the result of a call to
fegetenv or feholdexcept or equal to FE_DFL_ENV. This
call does not raise exceptions.
The feupdateenv function saves the currently raised excep
tions in its automatic storage, installs the floating-
point environment represented by the object pointed to by
envp, and then raises the saved exceptions. As before,
the object pointed to by envp must be known to be valid.