#include <math.h> int matherr(struct exception *exc); extern _LIB_VERSION_TYPE _LIB_VERSION;
The System V Interface Definition (SVID) specifies that various math functions should invoke a function called matherr() if a math exception is detected. This function is called before the math function returns; after matherr() returns, the system then returns to the math function, which in turn returns to the caller.
To employ matherr(), the programmer must define the _SVID_SOURCE feature test macro (before including any header files), and assign the value _SVID_ to the external variable _LIB_VERSION.
The system provides a default version of matherr(). This version does nothing, and returns zero (see below for the significance of this). The default matherr() can be overridden by a programmer-defined version, which will be invoked when an exception occurs. The function is invoked with one argument, a pointer to an exception structure, defined as follows:
struct exception {
int type; /* Exception type */
char *name; /* Name of function causing exception */
double arg1; /* 1st argument to function */
double arg2; /* 2nd argument to function */
double retval; /* Function return value */
}
The type field has one of the following values:
The arg1 and arg2 fields are the arguments supplied to the function (arg2 is undefined for functions that take only one argument).
The retval field specifies the return value that the math function will return to its caller. The programmer-defined matherr() can modify this field to change the return value of the math function.
If the matherr() function returns zero, then the system sets errno as described above, and may print an error message on standard error (see below).
If the matherr() function returns a nonzero value, then the system does not set errno, and doesn't print an error message.
The "Msg?" and "errno" columns describe the default behavior if matherr() returns zero. If the "Msg?" columns contains "y", then the system prints an error message on standard error.
The table uses the following notations and abbreviations:
| x first argument to function | |
| y second argument to function | |
| fin finite value for argument | |
| neg negative value for argument | |
| int integral value for argument | |
| o/f result overflowed | |
| u/f result underflowed | |
| |x| absolute value of x | |
| X_TLOSS is a constant defined in <math.h> |
| Function | Type | Result | Msg? | errno |
| acos(|x|>1) | DOMAIN | HUGE | y | EDOM |
| asin(|x|>1) | DOMAIN | HUGE | y | EDOM |
| atan2(0,0) | DOMAIN | HUGE | y | EDOM |
| acosh(x<1) | DOMAIN | NAN | y | EDOM |
| -HUGE_VAL | ||||
| cosh(fin) o/f | OVERFLOW | HUGE | n | ERANGE |
| sinh(fin) o/f | OVERFLOW | (x>0.0) ? | n | ERANGE |
| HUGE : -HUGE | ||||
| sqrt(x<0) | DOMAIN | 0.0 | y | EDOM |
| hypot(fin,fin) o/f | OVERFLOW | HUGE | n | ERANGE |
| exp(fin) o/f | OVERFLOW | HUGE | n | ERANGE |
| exp(fin) u/f | UNDERFLOW | 0.0 | n | ERANGE |
| exp2(fin) o/f | OVERFLOW | HUGE | n | ERANGE |
| exp2(fin) u/f | UNDERFLOW | 0.0 | n | ERANGE |
| exp10(fin) o/f | OVERFLOW | HUGE | n | ERANGE |
| exp10(fin) u/f | UNDERFLOW | 0.0 | n | ERANGE |
| j0(|x|>X_TLOSS) | TLOSS | 0.0 | y | ERANGE |
| j1(|x|>X_TLOSS) | TLOSS | 0.0 | y | ERANGE |
| jn(|x|>X_TLOSS) | TLOSS | 0.0 | y | ERANGE |
| y0(x>X_TLOSS) | TLOSS | 0.0 | y | ERANGE |
| y1(x>X_TLOSS) | TLOSS | 0.0 | y | ERANGE |
| yn(x>X_TLOSS) | TLOSS | 0.0 | y | ERANGE |
| y0(0) | DOMAIN | -HUGE | y | EDOM |
| y0(x<0) | DOMAIN | -HUGE | y | EDOM |
| y1(0) | DOMAIN | -HUGE | y | EDOM |
| y1(x<0) | DOMAIN | -HUGE | y | EDOM |
| yn(n,0) | DOMAIN | -HUGE | y | EDOM |
| yn(x<0) | DOMAIN | -HUGE | y | EDOM |
| lgamma(fin) o/f | OVERFLOW | HUGE | n | ERANGE |
| lgamma(-int) or | SING | HUGE | y | EDOM |
| lgamma(0) | ||||
| tgamma(fin) o/f | OVERFLOW | HUGE_VAL | n | ERANGE |
| tgamma(-int) | SING | NAN | y | EDOM |
| tgamma(0) | SING | copysign( | y | ERANGE |
| HUGE_VAL,x) | ||||
| log(0) | SING | -HUGE | y | EDOM |
| log(x<0) | DOMAIN | -HUGE | y | EDOM |
| log2(0) | SING | -HUGE | n | EDOM |
| log10(x<0) | DOMAIN | -HUGE | y | EDOM |
| pow(0.0,0.0) | DOMAIN | 0.0 | y | EDOM |
| pow(x,y) o/f | OVERFLOW | HUGE | n | ERANGE |
| pow(x,y) u/f | UNDERFLOW | 0.0 | n | ERANGE |
| pow(NaN,0.0) | DOMAIN | x | n | EDOM |
| 0**neg | DOMAIN | 0.0 | y | EDOM |
| scalb() o/f | OVERFLOW | (x>0.0) ? | n | ERANGE |
| HUGE_VAL : | ||||
| -HUGE_VAL | ||||
| scalb() u/f | UNDERFLOW | copysign( | n | ERANGE |
| 0.0,x) | ||||
| fmod(x,0) | DOMAIN | x | y | EDOM |
| remainder(x,0) | DOMAIN | NAN | y | EDOM |
| For an explanation of the terms used in this section, see | ||||
| allbox; | ||||
| lb lb lb | ||||
| l l l. | ||||
| Interface | Attribute | Value | ||
matherr() | Thread safety | MT-Safe |
The following example run, where log(3) is given an argument of 0.0, does not use matherr():
$ ./a.out 0.0 errno: Numerical result out of range x=-inf
In the following run, matherr() is called, and returns 0:
$ ./a.out 0.0 0
matherr SING exception in log() function
args: 0.000000, 0.000000
retval: -340282346638528859811704183484516925440.000000
log: SING error
errno: Numerical argument out of domain
x=-340282346638528859811704183484516925440.000000
The message "log: SING error" was printed by the C library.
In the following run, matherr() is called, and returns a nonzero value:
$ ./a.out 0.0 1
matherr SING exception in log() function
args: 0.000000, 0.000000
retval: -340282346638528859811704183484516925440.000000
x=-340282346638528859811704183484516925440.000000
In this case, the C library did not print a message, and errno was not set.
In the following run, matherr() is called, changes the return value of the math function, and returns a nonzero value:
$ ./a.out 0.0 1 12345.0
matherr SING exception in log() function
args: 0.000000, 0.000000
retval: -340282346638528859811704183484516925440.000000
x=12345.000000
static int matherr_ret = 0; /* Value that matherr()
should return */
static int change_retval = 0; /* Should matherr() change
function's return value? */
static double new_retval; /* New function return value */
int
matherr(struct exception *exc)
{
fprintf(stderr, "matherr %s exception in %s() function\n",
(exc->type == DOMAIN) ? "DOMAIN" :
(exc->type == OVERFLOW) ? "OVERFLOW" :
(exc->type == UNDERFLOW) ? "UNDERFLOW" :
(exc->type == SING) ? "SING" :
(exc->type == TLOSS) ? "TLOSS" :
(exc->type == PLOSS) ? "PLOSS" : "???",
exc->name);
fprintf(stderr, " args: %f, %f\n",
exc->arg1, exc->arg2);
fprintf(stderr, " retval: %f\n", exc->retval);
if (change_retval)
exc->retval = new_retval;
return matherr_ret;
}
int
main(int argc, char *argv[])
{
double x;
if (argc < 2) {
fprintf(stderr, "Usage: %s <argval>"
" [<matherr-ret> [<new-func-retval>]]\n", argv[0]);
exit(EXIT_FAILURE);
}
if (argc > 2) {
_LIB_VERSION = _SVID_;
matherr_ret = atoi(argv[2]);
}
if (argc > 3) {
change_retval = 1;
new_retval = atof(argv[3]);
}
x = log(atof(argv[1]));
if (errno != 0)
perror("errno");
printf("x=%f\n", x);
exit(EXIT_SUCCESS);
}