matherr(3M) LIBRARY FUNCTIONS matherr(3M)
NAME
matherr - error-handling function
SYNOPSIS
cc [flag ...] file ... -lm [library ...]
#include <math.h>
int matherr (struct exception *x);
DESCRIPTION
matherr is invoked by functions in the math libraries when
errors are detected. Note that matherr is not invoked when
the -Xc compilation option is used. Users may define their
own procedures for handling errors, by including a function
named matherr in their programs. matherr must be of the
form described above. When an error occurs, a pointer to
the exception structure x will be passed to the user-
supplied matherr function. This structure, which is defined
in the math.h header file, is as follows:
struct exception {
int type;
char *name;
double arg1, arg2, retval;
};
The element type is an integer describing the type of error
that has occurred, from the following list of constants
(defined in the header file):
DOMAIN argument domain error
SING argument singularity
OVERFLOW overflow range error
UNDERFLOW underflow range error
TLOSS total loss of significance
PLOSS partial loss of significance
The element name points to a string containing the name of
the function that incurred the error. The variables arg1
and arg2 are the arguments with which the function was
invoked. retval is set to the default value that will be
returned by the function unless the user's matherr sets it
to a different value.
If the user's matherr function returns non-zero, no error
message will be printed, and errno will not be set.
If matherr is not supplied by the user, the default error-
handling procedures, described with the math functions
involved, will be invoked upon error. These procedures are
also summarized in the table below. In every case, errno is
1
matherr(3M) LIBRARY FUNCTIONS matherr(3M)
set to EDOM or ERANGE and the program continues.
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matherr(3M) LIBRARY FUNCTIONS matherr(3M)
___________________________________________________________________________________
| Default Error Handling Procedures |
|_____________________|___________________________________________________________|
| | Types of Errors |
|_____________________|________|_______|___________|____________|________|________|
| type | DOMAIN| SING | OVERFLOW | UNDERFLOW | TLOSS | PLOSS |
|_____________________|________|_______|___________|____________|________|________|
| errno | EDOM | EDOM | ERANGE | ERANGE | ERANGE| ERANGE|
|_____________________|________|_______|___________|____________|________|________|
|BESSEL: | - | - | - | - | M, 0 | - |
|y0, y1, yn (arg < 0) | M, -H | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|EXP, EXPF: | - | - | H | 0 | - | - |
|_____________________|________|_______|___________|____________|________|________|
|LOG, LOG10: | | | | | | |
|LOGF, LOG10F: | | | | | | |
| (arg < 0) | M, -H | - | - | - | - | - |
| (arg = 0) | M, -H | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|POW, POWF: | - | - | +H | 0 | - | - |
|neg ** non-int | M, 0 | - | - | - | - | - |
| 0 ** non-pos | M, 0 | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|SQRT, SQRTF: | M, 0 | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|FMOD, FMODF: | | | | | | |
| (arg2 = 0) | M, X | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|REMAINDER: | | | | | | |
| (arg2 = 0) | M, N | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|GAMMA, LGAMMA: | - | M, H | H | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|HYPOT: | - | - | H | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|SINH, SINHF: | - | - | +H | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|COSH, COSHF: | - | - | H | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|ASIN, ACOS, ATAN2: | | | | | | |
|ASINF, ACOSF, ATAN2F:| M, 0 | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|ACOSH: | M, N | - | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
|ATANH: | | | | | | |
| (|arg| > 1) | M, N | - | - | - | - | - |
| (|arg| = 1) | - | M, N | - | - | - | - |
|_____________________|________|_______|___________|____________|________|________|
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matherr(3M) LIBRARY FUNCTIONS matherr(3M)
_________________________________________________________________
| Abbreviations |
|M Message is printed (not with the -Xa or -Xc options). |
|H HUGE is returned (HUGEVAL with the -Xa or -Xc options). |
|-H -HUGE is returned (-HUGEVAL with the -Xa or -Xc options).|
|+H HUGE or -HUGE is returned. |
| (HUGEVAL or -HUGEVAL with the -Xa or -Xc options). |
|0 0 is returned. |
|X arg1 is returned. |
|N NaN is returned. |
|_______________________________________________________________|
EXAMPLE
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
matherr(register struct exception *x);
{
switch (x->type) {
case DOMAIN:
/* change sqrt to return sqrt(-arg1), not 0 */
if (!strcmp(x->name, "sqrt")) {
x->retval = sqrt(-x->arg1);
return (0); /* print message and set errno */
}
case SING:
/* all other domain or sing errors, print message and abort */
fprintf(stderr, "domain error in %s\n", x->name);
abort( );
case PLOSS:
/* print detailed error message */
fprintf(stderr, "loss of significance in %s(%g) = %g\n",
x->name, x->arg1, x->retval);
return (1); /* take no other action */
}
return (0); /* all other errors, execute default procedure */
}
NOTES
Error handling in -Xa and -Xt modes [see cc(1)] is described
more completely on individual math library pages.
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