matherr(3M) — MATHEMATICAL LIBRARY
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):
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.
| 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 | − | − | − | − |
| Abbreviations | |
| M | Message is printed (not with the −Xa or −Xc options). |
| H | HUGE is returned (HUGE_VAL with the −Xa or −Xc options). |
| −H | −HUGE is returned (−HUGE_VAL with the −Xa or −Xc options). |
| ±H | HUGE or −HUGE is returned. |
| (HUGE_VAL or −HUGE_VAL 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.
— Math Libraries