{
    "mode": "man",
    "parameter": "math_error",
    "section": "7",
    "url": "https://www.chedong.com/phpMan.php/man/math_error/7/json",
    "generated": "2026-11-08T03:29:05Z",
    "synopsis": "",
    "sections": {
        "NAME": {
            "content": "matherror - detecting errors from mathematical functions\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "",
            "subsections": [
                {
                    "name": "#include <math.h>",
                    "content": ""
                },
                {
                    "name": "#include <errno.h>",
                    "content": ""
                },
                {
                    "name": "#include <fenv.h>",
                    "content": ""
                }
            ]
        },
        "DESCRIPTION": {
            "content": "When  an error occurs, most library functions indicate this fact by returning a special value\n(e.g., -1 or NULL).  Because they typically return a floating-point number, the  mathematical\nfunctions  declared  in <math.h> indicate an error using other mechanisms.  There are two er‐\nror-reporting mechanisms: the older one sets errno; the newer one uses the floating-point ex‐\nception mechanism (the use of feclearexcept(3) and fetestexcept(3), as  outlined  below)  de‐\nscribed in fenv(3).\n\nA  portable  program that needs to check for an error from a mathematical function should set\nerrno to zero, and make the following call\n\nfeclearexcept(FEALLEXCEPT);\n\nbefore calling a mathematical function.\n\nUpon return from the mathematical function, if errno is nonzero, or the following  call  (see\nfenv(3)) returns nonzero\n\nfetestexcept(FEINVALID | FEDIVBYZERO | FEOVERFLOW |\nFEUNDERFLOW);\n\nthen an error occurred in the mathematical function.\n\nThe error conditions that can occur for mathematical functions are described below.\n",
            "subsections": [
                {
                    "name": "Domain error",
                    "content": "A  domain  error occurs when a mathematical function is supplied with an argument whose value\nfalls outside the domain for which the function is defined (e.g., giving a negative  argument\nto  log(3)).   When  a domain error occurs, math functions commonly return a NaN (though some\nfunctions return a different value in this case); errno is set  to  EDOM,  and  an  \"invalid\"\n(FEINVALID) floating-point exception is raised.\n"
                },
                {
                    "name": "Pole error",
                    "content": "A  pole  error  occurs when the mathematical result of a function is an exact infinity (e.g.,\nthe logarithm of 0 is negative infinity).  When a pole error occurs, the function returns the\n(signed) value HUGEVAL, HUGEVALF, or HUGEVALL, depending on whether  the  function  result\ntype  is  double,  float, or long double.  The sign of the result is that which is mathemati‐\ncally correct for the function.  errno is set  to  ERANGE,  and  a  \"divide-by-zero\"  (FEDI‐\nVBYZERO) floating-point exception is raised.\n"
                },
                {
                    "name": "Range error",
                    "content": "A range error occurs when the magnitude of the function result means that it cannot be repre‐\nsented  in  the  result  type  of  the function.  The return value of the function depends on\nwhether the range error was an overflow or an underflow.\n\nA floating result overflows if the result is finite, but is too large to represented  in  the\nresult type.  When an overflow occurs, the function returns the value HUGEVAL, HUGEVALF, or\nHUGEVALL,  depending  on  whether the function result type is double, float, or long double.\nerrno is set to ERANGE, and an \"overflow\" (FEOVERFLOW) floating-point exception is raised.\n\nA floating result underflows if the result is too small to be represented in the result type.\nIf an underflow occurs, a mathematical function typically returns 0.0 (C99  says  a  function\nshall return \"an implementation-defined value whose magnitude is no greater than the smallest\nnormalized  positive number in the specified type\").  errno may be set to ERANGE, and an \"un‐\nderflow\" (FEUNDERFLOW) floating-point exception may be raised.\n\nSome functions deliver a range error if the supplied argument value, or the correct  function\nresult,  would  be subnormal.  A subnormal value is one that is nonzero, but with a magnitude\nthat is so small that it can't be presented in normalized form (i.e., with a 1  in  the  most\nsignificant  bit  of the significand).  The representation of a subnormal number will contain\none or more leading zeros in the significand.\n"
                }
            ]
        },
        "NOTES": {
            "content": "The matherrhandling identifier specified by C99 and POSIX.1 is not supported by glibc.  This\nidentifier is supposed to indicate which of the two error-notification mechanisms (errno, ex‐\nceptions retrievable via fetestexcept(3)) is in use.  The standards require that at least one\nbe in use, but permit both to be available.  The current (glibc 2.8) situation under glibc is\nmessy.  Most (but not all) functions raise exceptions on errors.  Some also set errno.  A few\nfunctions set errno, but don't raise an exception.  A very few functions do neither.  See the\nindividual manual pages for details.\n\nTo avoid the complexities of using errno and fetestexcept(3) for error checking, it is  often\nadvised that one should instead check for bad argument values before each call.  For example,\nthe following code ensures that log(3)'s argument is not a NaN and is not zero (a pole error)\nor less than zero (a domain error):\n\ndouble x, r;\n\nif (isnan(x) || islessequal(x, 0)) {\n/* Deal with NaN / pole error / domain error */\n}\n\nr = log(x);\n\nThe discussion on this page does not apply to the complex mathematical functions (i.e., those\ndeclared  by  <complex.h>),  which  in  general  are not required to return errors by C99 and\nPOSIX.1.\n\nThe gcc(1) -fno-math-errno option causes the executable to  employ  implementations  of  some\nmathematical  functions that are faster than the standard implementations, but do not set er‐\nrno on error.  (The gcc(1) -ffast-math option also enables -fno-math-errno.)   An  error  can\nstill be tested for using fetestexcept(3).\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "gcc(1), errno(3), fenv(3), fpclassify(3), INFINITY(3), isgreater(3), matherr(3), nan(3)\n\ninfo libc\n\nLinux man-pages 6.7                          2023-10-31                                matherror(7)",
            "subsections": []
        }
    },
    "summary": "matherror - detecting errors from mathematical functions",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "gcc",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/gcc/1/json"
        },
        {
            "name": "errno",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/errno/3/json"
        },
        {
            "name": "fenv",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/fenv/3/json"
        },
        {
            "name": "fpclassify",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/fpclassify/3/json"
        },
        {
            "name": "INFINITY",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/INFINITY/3/json"
        },
        {
            "name": "isgreater",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/isgreater/3/json"
        },
        {
            "name": "matherr",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/matherr/3/json"
        },
        {
            "name": "nan",
            "section": "3",
            "url": "https://www.chedong.com/phpMan.php/man/nan/3/json"
        }
    ]
}