matherr(3M) matherr(3M)
NAME
matherr - error-handling function
SYNOPSIS
#include <math.h>
int matherr(x)
struct exception *x;
DESCRIPTION
matherr is invoked by functions in the Math Library when er-
rors are detected. 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;
double arg2;
double retval;
};
The element type is an integer describing the type of error
that has occurred, from the following list of constants (de-
fined 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 in-
voked. retval is set to the default value that will be re-
turned by the function unless the user's matherr sets it to
a different value.
If the user's matherr function returns nonzero, 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 in-
volved, will be invoked upon error. These procedures are
also summarized in the table below. In every case, errno is
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matherr(3M) matherr(3M)
set to EDOM or ERANGE and the program continues.
EXAMPLES
#include <math.h>
int
matherr(x)
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 */
}
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matherr(3M) matherr(3M)
DEFAULT ERROR HANDLING PROCEDURES
_______________________________________________________________
| Types of Errors
_______________________________________________________________
|
type DOMAIN|SING O
|VERFLOW U
|NDERFLOW T
|LOSS P
|LOSS
____________________|__________________________________________
| | | | |
errno |EDOM EDOM ERANGE ERANGE ERANGEERANGE
__________________________|_____|________|_________|_____|_____
|
BESSEL: - | - | - | - |M, 0 | *
|
y0, y1, yn (arg < 0)M, -H | - | - | - | - | -
____________________|__________________________________________
| | | | |
EXP: | - - H 0 - -
__________________________|_____|________|_________|_____|_____
|
LOG, LOG10: | | | | |
|
(arg < 0) M, -H | - | - | - | - | -
|
(arg = 0) - M
|, -H | - | - | - | -
____________________|__________________________________________
| | | | |
POW: | - - +H 0 - -
| | | | |
neg ** nonint M
|, 0 - - - - -
| | | | |
0 ** nonpos |
__________________________|_____|________|_________|_____|_____
|
SQRT: M, 0 | - | - | - | - | -
____________________|__________________________________________
| | | | |
GAMMA: | - M, H H - - -
__________________________|_____|________|_________|_____|_____
|
HYPOT: - | - | H | - | - | -
____________________|__________________________________________
| | | | |
SINH: | - - +H - - -
__________________________|_____|________|_________|_____|_____
|
COSH: - | - | H | - | - | -
____________________|__________________________________________
| | | | |
SIN, COS, TAN: | - - - - M, 0 *
__________________________|_____|________|_________|_____|_____
|
ASIN, ACOS, ATAN2: |M, 0 | - | - | - | - | -
_____________________________________________________
| ABBREVIATIONS |
| * As much as possible of the value is returned. |
| M Message is printed (EDOM error). |
| H HUGE is returned. |
| -H -HUGE is returned. |
| +H HUGE or -HUGE is returned. |
| 0 0 is returned. |
|____________________________________________________|
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