MATHERR(3)                 Linux Programmer's Manual                MATHERR(3)

       matherr - SVID math library exception handling

       #include <math.h>

       int matherr(struct exception *exc);


       Link with -lm.

       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 caller.

       To employ matherr(), the programmer must define the  _SVID_SOURCE  fea-
       ture  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  ver-
       sion,  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 EDOM.

       OVERFLOW    An overflow occurred.  In most cases, the value HUGE is re-
                   turned, and errno is set to ERANGE.

       UNDERFLOW   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 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

       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  math-
       err()  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 math-
       err() returns zero.  If the "Msg?" columns contains "y", then the  sys-
       tem 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

       For  an  explanation  of  the  terms  used  in  this  section,  see at-

       |Interface | Attribute     | Value   |
       |matherr() | Thread safety | MT-Safe |
       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 value:

           $ ./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

       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);

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

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       description of the project, information about reporting bugs,  and  the
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Linux                             2019-03-06                        MATHERR(3)
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