MATHERR(S) UNIX System V MATHERR(S)
Name
matherr - error-handling function
Syntax
#include <math.h>
int matherr (x)
struct exception *x;
Description
The matherr function is invoked by functions in the Math
Library when errors are detected. Users may define their
own procedures for handling errors by including a function
named matherr in their programs. The matherr function 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
set to EDOM or ERANGE and the program continues.
Example
#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 (C); /* take no other action */
}
return (0); /* all other errors, execute default procedure */
}
DEFAULT ERROR HANDLING PROCEDURES
___________________________________________________________________
Types of Errors
___________________________________________________________________
type DOMAIN SING OVERFLOW UNDERFLOW TLOSS PLOSS
___________________________________________________________________
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 ** non-int M, 0 - - - - -
0 ** non-pos
___________________________________________________________________
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.
Standards Conformance
matherr is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
and The X/Open Portability Guide II of January 1987.
(printed 6/20/89)