strtold, _strtold_l, wcstold, _wcstold_l

Converts strings to a long double-precision floating-point value.

long double strtold(
   const char *nptr,
   char **endptr 
long double _strtold_l(
   const char *nptr,
   char **endptr,
   _locale_t locale
long double wcstold(
   const wchar_t *nptr,
   wchar_t **endptr 
long double wcstold_l(
   const wchar_t *nptr,
   wchar_t **endptr,
   _locale_t locale


Null-terminated string to convert.


Pointer to the character that stops the scan.


The locale to use.

strtold returns the value of the floating-point number as a long double, except when the representation would cause an overflow—in that case, the function returns +/–HUGE_VALL. The sign of HUGE_VALL matches the sign of the value that cannot be represented. strtold returns 0 if no conversion can be performed or an underflow occurs.

wcstold returns values analogously to strtold. For both functions, errno is set to ERANGE if overflow or underflow occurs and the invalid parameter handler is invoked, as described in Parameter Validation.

For more information about return codes, see errno, _doserrno, _sys_errlist, and _sys_nerr.

Each function converts the input string nptr to a long double. The strtold function converts nptr to a long double-precision value. strtold stops reading the string nptr at the first character it cannot recognize as part of a number. This may be the terminating null character. The wide-character version of strtold is wcstold; its nptr argument is a wide-character string. Otherwise, these functions behave identically.

Generic-Text Routine Mappings

TCHAR.H routine

_UNICODE & _MBCS not defined

_MBCS defined

_UNICODE defined









The LC_NUMERIC category setting of the current locale determines the recognition of the radix character in nptr. For more information, see setlocale, _wsetlocale. The functions without the _l suffix use the current locale; _strtold_l and _wcstold_l are identical to _strtold and _wcstold except that they instead use the locale that's passed in. For more information, see Locale.

If endptr is not NULL, a pointer to the character that stopped the scan is stored at the location that's pointed to by endptr. If no conversion can be performed (no valid digits were found or an invalid base was specified), the value of nptr is stored at the location that's pointed to by endptr.

strtold expects nptr to point to a string of the following form:

[whitespace] [sign] [digits] [.digits] [ {d | D | e | E}[sign]digits]

A whitespace may consist of space and tab characters, which are ignored; sign is either plus (+) or minus (); and digits are one or more decimal digits. If no digits appear before the radix character, at least one must appear after the radix character. The decimal digits can be followed by an exponent, which consists of an introductory letter (d, D, e, or E) and an optionally signed integer. If neither an exponent part nor a radix character appears, a radix character is assumed to follow the last digit in the string. The first character that does not fit this form stops the scan.


Required header

strtold , _strtold_l


wcstold , _wcstold_l

<stdlib.h> or <wchar.h>

For additional compatibility information, see Compatibility.

// crt_strtold.c
// Build with: cl /W4 /Tc crt_strtold.c
// This program uses strtold to convert a
// string to a long double-precision value.

#include <stdlib.h>
#include <stdio.h>

int main( void )
   char *string;
   char *stopstring;
   long double x;

   string = "3.1415926535898This stopped it";
   x = strtold(string, &stopstring);
   printf("string = %s\n", string);
   printf("   strtold = %.13Lf\n", x);
   printf("   Stopped scan at: %s\n\n", stopstring);
string = 3.1415926535898This stopped it
   strtold = 3.1415926535898
   Stopped scan at: This stopped it