#include <math.h>
int matherr(exc) struct exception *exc;
The SVID (System V Interface Definition) specifies that certain libm functions call matherr() when exceptions are detected. Users may define their own mechanisms for handling exceptions, by including a function named matherr() in their programs. matherr() is of the form described above. When an exception occurs, a pointer to the exception structure exc 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 exception that has occurred, from the following list of constants (defined in the header file):
The element name points to a string containing the name of the function that incurred the exception. The elements 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 exception message will be printed, and errno will not be set.
If matherr() is not supplied by the user, the default matherr exception-handling mechanisms, summarized in the table below, will be invoked upon exception:
The facilities provided by matherr() are not available in situations such as compiling on a Sun-3 system with /usr/lib/f68881/libm.il or /usr/lib/ffpa/libm.il, in which case some libm functions are converted to atomic hardware operations. In these cases setting errno and calling matherr() are not worth the adverse performance impact, but regular ANSI/IEEE Std 754-1985 exception handling remains available. In any case errno is not a reliable error indicator in that it may be unexpectedly set by a function in a handler for an asynchronous signal.
+------------------------------------------------------------------------------------------------------+ | DEFAULT ERROR HANDLING PROCEDURES | | | +------------------------------------------------------------------------------------------------------+ | Types of Errors | +------------------------------+-------------------+------------------+---------------+----------------+ | <math.h> type | DOMAIN | SING | OVERFLOW | UNDERFLOW | +------------------------------+-------------------+------------------+---------------+----------------+ |errno | EDOM | EDOM | ERANGE | ERANGE | +------------------------------+-------------------+------------------+---------------+----------------+ |IEEE Exception | Invalid Operation | Division by Zero | Overflow | Underflow | +------------------------------+-------------------+------------------+---------------+----------------+ |<floatingpoint.h> type | fp_invalid | fp_division | fp_overflow | fp_underflow | | | | | | | +------------------------------+-------------------+------------------+---------------+----------------+ |ACOS, ASIN: | M, NaN | - | - | - | +------------------------------+-------------------+------------------+---------------+----------------+ |ATAN2(0,0): | M, ±0.0 or ± | - | - | - | +------------------------------+-------------------+------------------+---------------+----------------+ |BESSEL: | | | | | |y0, y1, yn (x < 0) | M, NaN | - | - | - | |y0, y1, yn (x = 0) | - | M, - | - | - | +------------------------------+-------------------+------------------+---------------+----------------+ |COSH, SINH: | - | - | IEEE Overflow | - | +------------------------------+-------------------+------------------+---------------+----------------+ |EXP: | - | - | IEEE Overflow | IEEE Underflow | +------------------------------+-------------------+------------------+---------------+----------------+ |HYPOT: | - | - | IEEE Overflow | - | +------------------------------+-------------------+------------------+---------------+----------------+ |LGAMMA: | - | M, + | IEEE Overflow | - | +------------------------------+-------------------+------------------+---------------+----------------+ |LOG, LOG10: | | | | | | (x < 0) | M, NaN | - | - | - | | (x = 0) | - | M, - | - | - | +------------------------------+-------------------+------------------+---------------+----------------+ |POW: | | | | | |usual cases | - | - | IEEE Overflow | IEEE Underflow | |(x < 0) ** (y not an integer) | M, NaN | - | - | - | | 0 ** 0 | M, 1.0 | - | - | - | | 0 ** (y < 0) | - | M, ± | - | - | +------------------------------+-------------------+------------------+---------------+----------------+ |SQRT: | M, NaN | - | - | - | +------------------------------+-------------------+------------------+---------------+----------------+
+--------------------------------------------------------------------+ | ABBREVIATIONS | | | +--------------------------------------------------------------------+ | | | M Message is printed (EDOM exception). | | NaN IEEE NaN result and invalid operation exception. | | IEEE result and division-by-zero exception. | |IEEE Overflow IEEE Overflow result and exception. | |IEEE Underflow IEEE Underflow result and exception. | | Closest machine-representable approximation to pi. | +--------------------------------------------------------------------+
The interaction of
IEEE
arithmetic and
matherr()
is not defined when executing under
IEEE
rounding modes other than the default
round to nearest:
matherr()
may not be called on overflow or underflow,
and the Sun-provided
matherr()
may return results that differ from those in this table.
#include <math.h> int matherr(x) register struct exception *x; { switch (x->type) { case DOMAIN: /* change sqrt to return sqrt(-arg1), not NaN */ if (!strcmp(x->name, "sqrt")) { x->retval = sqrt(-x->arg1); return (0); /* print message and set errno */ } /* fall through */ case SING: /* all other domain or sing exceptions, print message and abort */ fprintf(stderr, "domain exception in %s\n", x->name); abort( ); break; } return (0); /* all other exceptions, execute default procedure */ }
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