_atodbl, _atodbl_l, _atoldbl, _atoldbl_l, _atoflt, _atoflt_l

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12/18/2017

The latest version of this topic can be found at _atodbl, _atodbl_l, _atoldbl, _atoldbl_l, _atoflt, _atoflt_l.

Converts a string to a double (_atodbl), long double (_atoldbl), or float (_atoflt).

Syntax

int _atodbl(  
   _CRT_DOUBLE * value,  
   char * str  
);  
int _atodbl_l (  
   _CRT_DOUBLE * value,  
   char * str,  
   locale_t locale  
);  
int _atoldbl(  
   _LDOUBLE * value,  
   char * str  
);  
int _atoldbl_l (  
   _LDOUBLE * value,  
   char * str,  
   locale_t locale  
);  
int _atoflt(  
   _CRT_FLOAT * value,  
   const char * str  
);  
int _atoflt_l(  
   _CRT_FLOAT * value,  
   const char * str,  
   locale_t locale  
);

Parameters

value
The double, long double, or float value that's produced by converting the string to a floating-point value. These values are wrapped in a structure.

str
The string to be parsed to convert into a floating-point value.

locale
The locale to use.

Return Value

Returns 0 if successful. Possible error codes are _UNDERFLOW or _OVERFLOW, which are defined in the header file Math.h.

Remarks

These functions convert a string to a floating-point value. The difference between these functions and the atof family of functions is that these functions do not generate floating-point code and do not cause hardware exceptions. Instead, error conditions are reported as error codes.

If a string does not have a valid interpretation as a floating-point value, value is set to zero and the return value is zero.

The versions of these functions that have the _l suffix are identical the versions that don't have the suffix, except that they use the locale parameter that's passed in instead of the current thread locale.

Requirements

Routines	Required header
`_atodbl`, `_atoldbl`, `_atoflt` `_atodbl_l`, `_atoldbl_l`, `_atoflt_l`	<stdlib.h>

Example

// crt_atodbl.c  
// Uses _atodbl to convert a string to a double precision  
// floating point value.  
  
#include <stdlib.h>  
#include <stdio.h>  
  
int main()  
{  
   char str1[256] = "3.141592654";  
   char abc[256] = "abc";  
   char oflow[256] = "1.0E+5000";  
   _CRT_DOUBLE dblval;  
   _CRT_FLOAT fltval;  
   int retval;  
  
   retval = _atodbl(&dblval, str1);  
  
   printf("Double value: %lf\n", dblval.x);  
   printf("Return value: %d\n\n", retval);  
  
   retval = _atoflt(&fltval, str1);  
   printf("Float value: %f\n", fltval.f);  
   printf("Return value: %d\n\n", retval);  
  
   // A non-floating point value: returns 0.  
   retval = _atoflt(&fltval, abc);  
   printf("Float value: %f\n", fltval.f);  
   printf("Return value: %d\n\n", retval);  
  
   // Overflow.  
   retval = _atoflt(&fltval, oflow);  
   printf("Float value: %f\n", fltval.f);  
   printf("Return value: %d\n\n", retval);  
  
   return 0;  
}

Double value: 3.141593  
Return value: 0  
  
Float value: 3.141593  
Return value: 0  
  
Float value: 0.000000  
Return value: 0  
  
Float value: 1.#INF00  
Return value: 3

共用方式為