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

NAME
       matherr - SVID math library exception handling

SYNOPSIS
       #include <math.h>

       int matherr(struct exception *exc);

       extern _LIB_VERSION_TYPE _LIB_VERSION;

       Link with -lm.

DESCRIPTION
       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 feature test macro (before including any header files), and assign the value _SVID_ to  the  ex‐
       ternal 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 num‐
                   ber), 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 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 mes‐
       sage 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 :
                                        -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
         lgamma(0)
       tgamma(fin) o/f      OVERFLOW    HUGE_VAL        n     ERANGE
       tgamma(-int)         SING        NAN             y     EDOM
       tgamma(0)            SING        copysign(       y     ERANGE
                                        HUGE_VAL,x)
       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 :
                                        -HUGE_VAL
       scalb() u/f          UNDERFLOW   copysign(       n     ERANGE
                                          0.0,x)
       fmod(x,0)            DOMAIN      x               y     EDOM
       remainder(x,0)       DOMAIN      NAN             y     EDOM

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”
       β”‚Interface                                                                                                                             β”‚ Attribute     β”‚ Value   β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚matherr()                                                                                                                             β”‚ Thread safety β”‚ MT-Safe β”‚
       β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜

EXAMPLES
       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
           x=-inf

       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
           x=-340282346638528859811704183484516925440.000000

       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
           x=-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
           x=12345.000000

   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 */

       int
       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" : "???",
                   exc->name);
           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;
       }

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

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

           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)
               perror("errno");

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

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

Linux                                                                          2021-03-22                                                                     MATHERR(3)