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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |ATTRIBUTES |EXAMPLES |SEE ALSO |COLOPHON | |
matherr(3) Library Functions Manualmatherr(3)matherr - SVID math library exception handling
Math library (libm,-lm)
#include <math.h>[[deprecated]] int matherr(struct exception *exc);[[deprecated]] extern _LIB_VERSION_TYPE _LIB_VERSION;
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 inmath_error(7) andfenv(3). This page documents thematherr() 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 calledmatherr() if a math exception is detected. This function is called before the math function returns; aftermatherr() returns, the system then returns to the math function, which in turn returns to the caller. To employmatherr(), the programmer must define the_SVID_SOURCE feature test macro (before includingany header files), and assign the value_SVID_to the external variable_LIB_VERSION. The system provides a default version ofmatherr(). This version does nothing, and returns zero (see below for the significance of this). The defaultmatherr() 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 anexception 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 */ } Thetype field has one of the following values:DOMAINA 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 toEDOM.SINGA pole error occurred (the function result is an infinity). The return value in most cases isHUGE(the largest single precision floating-point number), appropriately signed. In most cases,errno is set toEDOM.OVERFLOW An overflow occurred. In most cases, the valueHUGEis returned, anderrno is set toERANGE.UNDERFLOW An underflow occurred. 0.0 is returned, anderrno is set toERANGE.TLOSSTotal loss of significance. 0.0 is returned, anderrno is set toERANGE.PLOSSPartial loss of significance. This value is unused on glibc (and many other systems). Thearg1 andarg2 fields are the arguments supplied to the function (arg2 is undefined for functions that take only one argument). Theretval field specifies the return value that the math function will return to its caller. The programmer-definedmatherr() can modify this field to change the return value of the math function. If thematherr() function returns zero, then the system setserrno as described above, and may print an error message on standard error (see below). If thematherr() function returns a nonzero value, then the system does not seterrno, and doesn't print an error message.Math functions that employ matherr() The table below lists the functions and circumstances in whichmatherr() is called. The "Type" column indicates the value assigned toexc->type when callingmatherr(). The "Result" column is the default return value assigned toexc->retval. The "Msg?" and "errno" columns describe the default behavior ifmatherr() 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 : -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 EDOMFor an explanation of the terms used in this section, seeattributes(7). ┌──────────────────────────────────────┬───────────────┬─────────┐ │Interface│Attribute│Value│ ├──────────────────────────────────────┼───────────────┼─────────┤ │matherr() │ Thread safety │ MT-Safe │ └──────────────────────────────────────┴───────────────┴─────────┘
The example program demonstrates the use ofmatherr() when callinglog(3). The program takes up to three command-line arguments. The first argument is the floating-point number to be given tolog(3). If the optional second argument is provided, then_LIB_VERSIONis set to_SVID_so thatmatherr() is called, and the integer supplied in the command-line argument is used as the return value frommatherr(). If the optional third command-line argument is supplied, then it specifies an alternative return value thatmatherr() should assign as the return value of the math function. The following example run, wherelog(3) is given an argument of 0.0, does not usematherr(): $./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, anderrno 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=12345.000000Program 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); }fenv(3),math_error(7),standards(7)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17matherr(3)Pages that refer to this page:math_error(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |