matherr.3m

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3M 代码 · 共 176 行

.\" SCCSID: @(#)matherr.3m	8.1	9/11/90
.TH matherr 3m VAX
.SH Name
matherr \- error-handling function for System V math library
.SH Syntax
.PP
.B #include <math.h>
.PP
.B int matherr (x)
.br
.B struct exception \(**x;
.SH Description
.NXR "matherr subroutine"
.NXR "error function" "System V and"
The
.PN 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
.PN matherr
in their programs.
The
.PN matherr
subroutine must be of the form described above.
A pointer to the exception structure
.I x\^
will be passed to the user-supplied
.PN matherr
function when an error occurs.
This structure,
which is defined in the <math.h> header file, is as follows:
.EX
struct exception {
	int type;
	char \(**name;
	double arg1, arg2, retval;
};
.EE
.PP
The element
.I type\^
is an integer describing the type of error that has occurred, from the
following list of constants (defined in the header file):
.EX
DOMAIN     domain error
SING       singularity
OVERFLOW   overflow
UNDERFLOW  underflow
TLOSS      total loss of significance
PLOSS      partial loss of significance
.EE
.PP
The element
.I name\^
points to a string containing
the name of the function that had the error.
The variables
.I arg1\^
and
.I arg2\^
are the arguments to the function that had the error.
The
.I retval\^
is a double that is returned by the function
having the error.
If it supplies a return value, the user's
.PN matherr\^
must return nonzero.
If the default error value is to be returned, the user's
.PN matherr\^
must return 0.
.PP
If
.PN 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,
.I errno\^
is set to nonzero and the program continues.
.SH Examples
.NXR(e) "matherr subroutine" "using"
.EX 0
matherr(x)
register struct exception \(**x;
{
	switch (x\->type) {
	case DOMAIN:
	case SING: /\(** print message and abort \(**/
		fprintf(stderr, "domain error in %s\en", x\->name);
		abort( );
	case OVERFLOW:
		if (!strcmp("exp", x\->name)) {
			/\(** if exp, print message, return the argument \(**/
			fprintf(stderr, "exp of %f\en", 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\en", x\->name);
		x\->retval = 0;
		break;
	}
	return (1);
}
.EE
.PP
.in 0
.TS
expand box ;
cB s s s s s s
c | cI s s s s s
c | c | c | c | c | c | c
l | c | c | c | c | c | c .
DEFAULT ERROR HANDLING PROCEDURES
.NXR(t) "matherr subroutine" "error-handling procedures"

_
	Types of Errors
_
	DOMAIN	SING	OVERFLOW 	UNDERFLOW 	TLOSS 	PLOSS 
_
BESSEL:	\-	\-	H	0	M, 0	\(**
y0, y1, yn	M, \-H 	\-	\-	\-	\-	\-
 (neg. no.)
_
EXP:	\-	\-	H	0	\-
_
POW:	\-	\-	H	0	\-	\-
(neg.)\(**\(**(non-	M, 0 	\-	\-	\-	\-	\-
 int.), 0\(**\(**0
_
LOG:
log(0):	\-	M, \-H 	\-	\-	\-	\-
log(neg.):	 M, \-H	\-	\-	\-	\-	\-
_
SQRT:	M, 0	\-	\-	\-	\-	\-
_
GAMMA:	\-	M, H	\-	\-	\-	\-
_
HYPOT:	\-	\-	H	\-	\-	\-
_
SINH, COSH:	\-	\-	H	\-	\-	\-
_
SIN, COS:	\-	\-	\-	\-	M, 0	\(**
_
TAN:	\-	\-	H	\-	M, 0	\(**
_
ACOS, ASIN:	M, 0	\-	\-	\-	\-	\-
.TE
.PP
.TS
box;
cB s
c l .
ABBREVIATIONS
 \(**	As much as possible of the value is returned.
 M	Message is printed.
 H	HUGE is returned.
 \-H	\-HUGE is returned.
 0	0 is returned.
.TE