wcstof, wcstod, wcstold

Defined in header `<wchar.h>`
float wcstof( const wchar_t* restrict str, wchar_t** restrict str_end );		(since C99)
double wcstod( const wchar_t* str, wchar_t** str_end );		(since C95) (until C99)
double wcstod( const wchar_t* restrict str, wchar_t** restrict str_end );		(since C99)
long double wcstold( const wchar_t* restrict str, wchar_t** restrict str_end );		(since C99)

Interprets a floating-point value in a wide string pointed to by str.

Function discards any whitespace characters (as determined by iswspace) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid floating-point representation and converts them to a floating-point value. The valid floating-point value can be one of the following:

decimal floating-point expression. It consists of the following parts:

(optional) plus or minus sign
nonempty sequence of decimal digits optionally containing decimal-point character (as determined by the current C locale) (defines significand)
(optional) e or E followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 10)

hexadecimal floating-point expression. It consists of the following parts:

(optional) plus or minus sign
0x or 0X
nonempty sequence of hexadecimal digits optionally containing a decimal-point character (as determined by the current C locale) (defines significand)
(optional) p or P followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 2)

infinity expression. It consists of the following parts:

(optional) plus or minus sign
INF or INFINITY ignoring case

not-a-number expression. It consists of the following parts:

(optional) plus or minus sign
NAN or NAN(char_sequence) ignoring case of the NAN part. char_sequence can only contain digits, Latin letters, and underscores. The result is a quiet NaN floating-point value.

(since C99)

any other expression that may be accepted by the currently installed C locale

The functions sets the pointer pointed to by str_end to point to the wide character past the last character interpreted. If str_end is a null pointer, it is ignored.

#include <errno.h>
#include <stdio.h>
#include <wchar.h>
 
int main(void)
{
    const wchar_t* p = L"111.11 -2.22 0X1.BC70A3D70A3D7P+6  1.18973e+4932zzz";
    printf("Parsing L\"%ls\":\n", p);
    wchar_t* end;
    for (double f = wcstod(p, &end); p != end; f = wcstod(p, &end))
    {
        printf("'%.*ls' -> ", (int)(end-p), p);
        p = end;
        if (errno == ERANGE){
            printf("range error, got ");
            errno = 0;
        }
        printf("%f\n", f);
    }
}

Output:

Parsing L"111.11 -2.22 0X1.BC70A3D70A3D7P+6  1.18973e+4932zzz":
'111.11' -> 111.110000
' -2.22' -> -2.220000
' 0X1.BC70A3D70A3D7P+6' -> 111.110000
'  1.18973e+4932' -> range error, got inf

References

C23 standard (ISO/IEC 9899:2024):

7.29.4.1.1 The wcstod, wcstof, and wcstold functions (p: TBD)

C17 standard (ISO/IEC 9899:2018):

7.29.4.1.1 The wcstod, wcstof, and wcstold functions (p: TBD)

C11 standard (ISO/IEC 9899:2011):

7.29.4.1.1 The wcstod, wcstof, and wcstold functions (p: 426-428)

C99 standard (ISO/IEC 9899:1999):

7.24.4.1.1 The wcstod, wcstof, and wcstold functions (p: 372-374)

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wcstof, wcstod, wcstold

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str	-	pointer to the null-terminated wide string to be interpreted
str_end	-	pointer to a pointer to a wide character.

strtofstrtodstrtold (C99)(C99)	converts a byte string to a floating-point value (function) [edit]
C++ documentation for wcstof, wcstod, wcstold