matherr(3) — Linux manual page


matherr(3)              Library Functions Manual              matherr(3)

NAME         top

       matherr - SVID math library exception handling

LIBRARY         top

       Math library (libm, -lm)

SYNOPSIS         top

       #include <math.h>

       [[deprecated]] int matherr(struct exception *exc);

       [[deprecated]] extern _LIB_VERSION_TYPE _LIB_VERSION;

DESCRIPTION         top

       Note: the mechanism described in this page is no longer supported
       by glibc.  Before glibc 2.27, it had been marked as obsolete.
       Since glibc 2.27, the mechanism has been removed altogether.  New
       applications should use the techniques described in math_error(7)
       and fenv(3).  This page documents the matherr() mechanism as an
       aid for maintaining and porting older applications.

       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

       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:

       DOMAIN A domain error occurred (the function argument was outside
              the range for which the function is defined).  The return
              value depends on the function; errno is set to EDOM.

       SING   A pole error occurred (the function result is an
              infinity).  The return value in most cases is HUGE (the
              largest single precision floating-point number),
              appropriately signed.  In most cases, errno is set to

              An overflow occurred.  In most cases, the value HUGE is
              returned, and errno is set to ERANGE.

              An underflow occurred.  0.0 is returned, and errno is set
              to ERANGE.

       TLOSS  Total loss of significance.  0.0 is returned, and errno is
              set to ERANGE.

       PLOSS  Partial loss of significance.  This value is unused on
              glibc (and many other systems).

       The arg1 and arg2 fields are the arguments supplied to the
       function (arg2 is undefined for functions that take only one

       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.

   Math functions that employ matherr()
       The table below lists the functions and circumstances in which
       matherr() is called.  The "Type" column indicates the value
       assigned to exc->type when calling matherr().  The "Result"
       column is the default return value assigned to exc->retval.

       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
       atanh(|x|>1)         DOMAIN      NAN             y     EDOM
       atanh(|x|==1)        SING        (x>0.0)?        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
       tgamma(fin) o/f      OVERFLOW    HUGE_VAL        n     ERANGE
       tgamma(-int)         SING        NAN             y     EDOM
       tgamma(0)            SING        copysign(       y     ERANGE
       log(0)               SING        -HUGE           y     EDOM
       log(x<0)             DOMAIN      -HUGE           y     EDOM
       log2(0)              SING        -HUGE           n     EDOM
       log2(x<0)            DOMAIN      -HUGE           n     EDOM
       log10(0)             SING        -HUGE           y     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
       neg**non-int         DOMAIN      0.0             y     EDOM
       scalb() o/f          OVERFLOW    (x>0.0) ?       n     ERANGE
                                        HUGE_VAL :
       scalb() u/f          UNDERFLOW   copysign(       n     ERANGE
       fmod(x,0)            DOMAIN      x               y     EDOM
       remainder(x,0)       DOMAIN      NAN             y     EDOM

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ matherr()                           │ Thread safety │ MT-Safe │

EXAMPLES         top

       The example program demonstrates the use of matherr() when
       calling log(3).  The program takes up to three command-line
       arguments.  The first argument is the floating-point number to be
       given to log(3).  If the optional second argument is provided,
       then _LIB_VERSION is set to _SVID_ so that matherr() is called,
       and the integer supplied in the command-line argument is used as
       the return value from matherr().  If the optional third command-
       line argument is supplied, then it specifies an alternative
       return value that matherr() should assign as the return value of
       the math function.

       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

       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

       The message "log: SING error" was printed by the C library.

       In the following run, matherr() is called, and returns a nonzero

           $ ./a.out 0.0 1
           matherr SING exception in log() function
                   args:   0.000000, 0.000000
                   retval: -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

   Program source

       #define _SVID_SOURCE
       #include <errno.h>
       #include <math.h>
       #include <stdio.h>
       #include <stdlib.h>

       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 */

       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" : "???",
           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;

       main(int argc, char *argv[])
           double x;

           if (argc < 2) {
               fprintf(stderr, "Usage: %s <argval>"
                       " [<matherr-ret> [<new-func-retval>]]\n", argv[0]);

           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)

           printf("x=%f\n", x);

SEE ALSO         top

       fenv(3), math_error(7), standards(7)

Linux man-pages (unreleased)     (date)                       matherr(3)

Pages that refer to this page: math_error(7)