strtof, _strtof_l, wcstof, _wcstof_l

Converts strings to a single-precision floating-point value.

Syntax

float strtof(
   const char *strSource,
   char **endptr
);
float _strtof_l(
   const char *strSource,
   char **endptr,
   _locale_t locale
);
float wcstof(
   const wchar_t *strSource,
   wchar_t **endptr
);
float wcstof_l(
   const wchar_t *strSource,
   wchar_t **endptr,
   _locale_t locale
);

Parameters

strSource
Null-terminated string to convert.

endptr
Pointer to the character that stops the scan.

locale
The locale to use.

Return value

strtof returns the value of the floating-point number, except when the representation would cause an overflow, in which case the function returns +/-HUGE_VALF. The sign of HUGE_VALF matches the sign of the value that can't be represented. strtof returns 0 if no conversion can be performed or an underflow occurs.

wcstof returns values analogously to strtof. 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.

Remarks

Each function converts the input string strSource to a float. The strtof function converts strSource to a single-precision value. strtof stops reading the string strSource at the first character it can't recognize as part of a number. This character may be the terminating null character. wcstof is a wide-character version of strtof; its strSource argument is a wide-character string. Otherwise, these functions behave identically.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Generic-text routine mappings

The LC_NUMERIC category setting of the current locale determines recognition of the radix character in strSource; for more information, see setlocale, _wsetlocale. The functions that don't have the _l suffix use the current locale; the ones that have the suffix are identical except that they use the locale that's passed in instead. For more information, see Locale.

If endptr isn't 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 strSource is stored at the location that's pointed to by endptr.

strtof expects strSource to point to a string of the following form:

[whitespace] [sign] [digits] [.digits] [{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 (e or E) and an optionally signed integer. If no exponent part or radix character appears, a radix character is assumed to follow the last digit in the string. The first character that doesn't fit this form stops the scan.

The UCRT versions of these functions don't support conversion of Fortran-style (d or D) exponent letters. This non-standard extension was supported by earlier versions of the CRT, and may be a breaking change for your code.

Requirements

For more compatibility information, see Compatibility.

Example

// crt_strtof.c
// This program uses strtof to convert a
// string to a single-precision value.

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

int main( void )
{
   char *string;
   char *stopstring;
   float x;

   string = "3.14159This stopped it";
   x = strtof(string, &stopstring);
   printf("string = %s\n", string);
   printf("   strtof = %f\n", x);
   printf("   Stopped scan at: %s\n\n", stopstring);
}

string = 3.14159This stopped it
   strtof = 3.141590
   Stopped scan at: This stopped it

See also

Data conversion
Math and floating-point support
Interpretation of multibyte-character sequences
Locale
String to numeric value functions
strtod, _strtod_l, wcstod, _wcstod_l
strtol, wcstol, _strtol_l, _wcstol_l
strtoul, _strtoul_l, wcstoul, _wcstoul_l
atof, _atof_l, _wtof, _wtof_l
localeconv
_create_locale, _wcreate_locale
_free_locale