matherr, _matherrl

raw OCR

User-modifiable math error handler.

Defined in header <math.h>

Syntax

#include <math.h>
int matherr(struct exception *e);
int _matherrl(struct  exceptionl *e);

Portability

DOS	UNIX	Windows	ANSI C	C++ only
■		■

Remarks

matherr is called when an error is generated by the math library.

_matherrl is the long double version; it is called when an error is generated by the long double math functions.

matherr and _matherrl each serve as a user hook (a function that can be customized by the user) that you can replace by writing your own math error handling routine — see the following example of a user-defined matherr implementation.

matherr and _matherrl are useful for trapping domain and range errors caused by the math functions. They do not trap floating-point exceptions, such as division by zero. See signal for trapping such errors.

You can define your own matherr or _matherrl routine to be a custom error handler (such as one that catches and resolves certain types of errors); this customized function overrides the default version in the C library. The customized matherr or _matherrl should return 0 if it fails to resolve the error, or nonzero if the error is resolved. When matherr or _matherrl return nonzero, no error message is printed and the global variable errno is not changed.

Here are the exception and _exceptionl structures (defined in math.h):

struct exception { int type; char *Function; double argl, arg2, retval; }; struct _exceptionl { int type; char *Function; long double argl, arg2, retval; };■ The members of the exception and _exceptionl structures are shown in the following table:

Member What it is (or represents)

type	The type of mathematical error that occurred; an enum type defined in the typedef jnexcep (see definition after this list).
name	A pointer to a null-terminated string holding the name of the math library function that resulted in an error
argl,	The arguments (passed to the function name points to) that
arg2	caused the error; if only one argument was passed to the function, it is stored in argl.
retval	The default return value for matherr (or _matherrl); you can modify this value.

The typedef jnexcep, also defined in math.h, enumerates the following symbolic constants representing possible mathematical errors:

Symbolic

constant	l\/!athematical error
DOMAIN	Argument was not in domain of function, such as log(-l).
SING	Argument would result in a singularity, such as pow(0, -2).

OVERFLOW Argument would produce a function result greater than DBL_MAX (or LDBL_MAX), such as exp(lOOO). UNDERFLOW Argument would produce a function result less than DBL_M1N (or LDBL_M1N), such as exp(-lOOO).

TLOSS	Argument would produce function result with total loss of significant digits, such assin(10e70).

The macros DBL_MAX,	DBL_MIN,	LDBL_MAX,	and LDBL_MIN	are

defined in float.h.

The source code to the default nnatherr and _matherrl is on the Borland C++ distribution disks.

The UNIX-style matherr and _matherrl default behavior (printing a message and terminating) is not ANSI compatible. If you desire a UNIX-

style version of these routines, use MATHERR.C	and MATHERRL.C

provided on the Borland C++ distribution disks.

Return value

The default return value for matherr and _matherrl is 1 if the error is

UNDERFLOW	or TLOSS, 0 otherwise, matherr and _matherrl can also

modify e -> retval, which propagates back to the original caller.

When matherr and _matherrl return 0 (indicating that they were not able to resolve the error), the global variable errno is set to 0 and an error message is printed.

When matherr and _matherrl return nonzero (indicating that they were able to resolve the error), the global variable errno is not set and no messages are printed.

Example

#include <math.h>
#include <string.h>
#include <stdio.h>

int matherr (struct exception *a)
{
   if (a->type == DOMAIN)
      if (!strcmp(a->name, "sqrt")) {
         a->retval = sqrt (-(a->argl));
      return 1;
      }
   return 0;
}
int main (void)
{
   double X = -2.0, y;
   y = sqrt (x);
   printf ("Matherr corrected value: %lf\n",y);
   return 0;

Differences from modern implementations

Nothing recorded yet.

Modern references

Microsoft C runtime (search)

These are search links, not yet checked by hand.

Extraction notes

heading `matherr, matherri` read as `matherr, _matherrl`

Stable link: /3.1/math.h/matherr/ · short form /3.1/matherr/