NAME

matherr − math library error-handling function

SYNOPSIS

#include <math.h>

int matherr (x)
struct exception ∗x;

DESCRIPTION

matherr 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.  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):

DOMAINargument domain error
SINGargument singularity
OVERFLOWoverflow range error
UNDERFLOW underflow range error
TLOSStotal loss of significance
PLOSSpartial 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. 

NOTE

In the Sun environment, the facilities provided by matherr are only available when a program is built with the software floating point library, as there would be a substantial performance penalty imposed by providing these facilities with the libraries that support various Sun floating point hardware options. 

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 (1); /∗ take no other action ∗/
}
return (0); /∗ all other errors, execute default procedure ∗/
}

Sun Release 3.2  —  Last change: 30 April 1986