strtod函数

/****strtod.c - convert string to floating point number**       Copyright (c) Microsoft Corporation. All rights reserved.**Purpose:*       Convert character string to floating point number********************************************************************************/#include <cruntime.h>#include <stdlib.h>#include <fltintrn.h>#include <string.h>#include <ctype.h>#include <mbctype.h>#include <errno.h>#include <math.h>#include <internal.h>#include <locale.h>#include <mtdll.h>#include <setlocal.h>/****double strtod(nptr, endptr) - convert string to double**Purpose:*       strtod recognizes an optional string of tabs and spaces,*       then an optional sign, then a string of digits optionally*       containing a decimal point, then an optional e or E followed*       by an optionally signed integer, and converts all this to*       to a floating point number.  The first unrecognized*       character ends the string, and is pointed to by endptr.**Entry:*       nptr - pointer to string to convert**Exit:*       returns value of character string*       char **endptr - if not NULL, points to character which stopped*                       the scan**Exceptions:*       Input parameters are validated. Refer to the validation section of the function.********************************************************************************/extern "C" double __cdecl _strtod_l (        const char *nptr,        REG2 char **endptr,        _locale_t plocinfo        ){        struct _flt answerstruct;        FLT      answer;        double       tmp;        unsigned int flags;        REG1 char *ptr = (char *) nptr;        _LocaleUpdate _loc_update(plocinfo);        /* validation section */        if (endptr != NULL)        {            /* store beginning of string in endptr */            *endptr = (char *)nptr;        }        _VALIDATE_RETURN(nptr != NULL, EINVAL, 0.0);        /* scan past leading space/tab characters */        while ( _isspace_l((int)(unsigned char)*ptr, _loc_update.GetLocaleT()) )                ptr++;        /* let _fltin routine do the rest of the work */        /* ok to take address of stack variable here; fltin2 knows to use ss */        answer = _fltin2( &answerstruct, ptr, _loc_update.GetLocaleT());        if ( endptr != NULL )                *endptr = (char *) ptr + answer->nbytes;        flags = answer->flags;        if ( flags & (512 | 64)) {                /* no digits found or invalid format:                   ANSI says return 0.0, and *endptr = nptr */                tmp = 0.0;                if ( endptr != NULL )                        *endptr = (char *) nptr;        }        else if ( flags & (128 | 1) ) {                if ( *ptr == '-' )                        tmp = -HUGE_VAL;        /* negative overflow */                else                        tmp = HUGE_VAL;         /* positive overflow */                errno = ERANGE;        }        else if ( (flags & 256) && answer->dval == 0.0 ) {                tmp = 0.0;                      /* underflow (denormals OK) */                errno = ERANGE;        }        else                tmp = answer->dval;        return(tmp);}extern "C" double __cdecl strtod (        const char *nptr,        REG2 char **endptr        ){    return _strtod_l(nptr, endptr, NULL);}