HP-UX Reference (11i v2 03/08) - 3 Library Functions A-M (vol 6)

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feholdexcept(3M) feholdexcept(3M)

NAME

feholdexcept( ) - save ﬂoating-point environment

SYNOPSIS

#include <fenv.h>

int feholdexcept(fenv_t *envp);

DESCRIPTION

The feholdexcept()

function saves the current ﬂoating-point environment in the object pointed to by

the argument envp. This function also clears the ﬂoating-point exception ﬂags and disables all traps.

Use

feholdexcept()

with feupdateenv()

to hide spurious ﬂoating-point exceptions. Use it with

fesetenv() to hide all ﬂoating-point exceptions.

USAGE

To use this function, compile either with the default

-Ae option or with the -Aa and -D_HPUX_SOURCE

options. Make sure your program includes <fenv.h>

For Itanium(R)-based systems, specify

+Ofenvaccess on the compiler command line or place the call

to this function under the effect of an afﬁrmative

FENV_ACCESS pragma:

#pragma STDC FENV_ACCESS ON

If the FENV_ACCESS pragma is placed outside of any top-level declarations in a ﬁle, the pragma will

apply to all declarations in the compilation following the pragma until another FENV_ACCESS pragma

is encountered or until the end of the ﬁle is reached.

If the

FENV_ACCESS pragma is placed at the beginning of a block (compound statement), the pragma

will apply until another FENV_ACCESS pragma is encountered or until the end of the block is reached.

For PA-RISC, you might need to use the

+Onomoveflops compiler option in order to prevent optimiza-

tions that can undermine the speciﬁed behavior of this function.

Link in the math library by specifying

-lm on the compiler or linker command line.

For more information, see the HP-UX Floating-Point Guide.

RETURN VALUE

The

feholdexcept() function returns a zero value, indicating the successful disabling of any traps.

ERRORS

No errors are deﬁned.

EXAMPLES

Store the current ﬂoating-point environment in

holdenv, hide spurious underﬂow exceptions, and con-

tinue on any ﬂoating-point exceptions that occur until the call to feupdateenv()

is encountered.

#include <fenv.h>

/*...*/

fenv_t holdenv;

feholdexcept(&holdenv);

/* perform operations */

if (/* test for spurious underflow */)

feclearexcept(FE_UNDERFLOW);

feupdateenv(&holdenv); /* raise accumulated exceptions */