NAME

matherr − error-handling function for System V math library

SYNTAX

#include <math.h>

int matherr (x)
struct exception ∗x;

DESCRIPTION

The matherr subroutine is invoked by functions in the System V 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 subroutine must be of the form described above. A pointer to the exception structure x will be passed to the user-supplied matherr function when an error occurs. 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     domain error
SING       singularity
OVERFLOW   overflow
UNDERFLOW  underflow
TLOSS      total loss of significance
PLOSS      partial loss of significance

The element name points to a string containing the name of the function that had the error.  The variables arg1 and arg2 are the arguments to the function that had the error.  The retval is a double that is returned by the function having the error.  If it supplies a return value, the user’s matherr must return nonzero. If the default error value is to be returned, the user’s matherr must return 0.

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 nonzero and the program continues. 

EXAMPLE

matherr(x)
register struct exception ∗x;
{
switch (x−>type) {
case DOMAIN:
case SING: /∗ print message and abort ∗/
fprintf(stderr, "domain error in %s\n", x−>name);
abort( );
case OVERFLOW:
if (!strcmp("exp", x−>name)) {
/∗ if exp, print message, return the argument ∗/
fprintf(stderr, "exp of %f\n", x−>arg1);
x−>retval = x−>arg1;
} else if (!strcmp("sinh", x−>name)) {
/∗ if sinh, set errno, return 0 ∗/
errno = ERANGE;
x−>retval = 0;
} else
/∗ otherwise, return HUGE ∗/
x−>retval = HUGE;
break;
case UNDERFLOW:
return (0); /∗ execute default procedure ∗/
case TLOSS:
case PLOSS:
/∗ print message and return 0 ∗/
fprintf(stderr, "loss of significance in %s\n", x−>name);
x−>retval = 0;
break;
}
return (1);
}