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

       matherr - SVID math library exception handling

       #define _SVID_SOURCE             /* See feature_test_macros(7) */
       #include <math.h>

       int matherr(struct exception *exc);


       Link with -lm.

       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.

       The matherr() mechanism is supported by glibc, but is now obsolete: new
       applications should use the techniques described in  math_error(7)  and
       fenv(3).   This  page documents the glibc matherr() mechanism as an aid
       for maintaining and porting older applications.

       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
                   returned, 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

   Multithreading (see pthreads(7))
       The matherr() function is thread-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)

       This page is part of release 3.74 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at

Linux                             2014-06-13                        MATHERR(3)

Czas wygenerowania: 0.00026 sek.

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