std::wcstof, std::wcstod, std::wcstold

 

C++

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Technical Specifications

 

Strings library

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Wide strings

Classes

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Null-terminated wide strings

Functions
Character manipulation
iswalnum iswalpha iswlower iswupper iswdigit iswxdigit iswblank (C++11) wctype iswctype	iswcntrl iswgraph iswspace iswprint iswpunct towlower towupper wctrans towctrans
Conversions to numeric formats
wcstolwcstoll wcstoulwcstoull	wcstofwcstodwcstold wcstoimaxwcstouimax (C++11)(C++11)
String manipulation
wcslen wcscpy wcsncpy wcscat wcsncat wcscmp wcscoll wcsncmp	wcsxfrm wcschr wcsrchr wcspbrk wcsspn wcscspn wcsstr wcstok
Array manipulation
wmemcpy
wmemmove
wmemcmp
wmemchr
wmemset

 

Defined in header <cwchar>
float       wcstof( const wchar_t* str, wchar_t** str_end );		(since C++11)
double      wcstod( const wchar_t* str, wchar_t** str_end );
long double wcstold( const wchar_t* str, wchar_t** str_end );		(since C++11)

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

Function discards any whitespace characters (as determined by std::isspace()) 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)

• binary 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)

• 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 alphanumeric characters. The result is a quiet NaN floating-point value.

• 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 NULL, it is ignored.

Parameters

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

Return value

Floating point value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, ​0​ is returned.

Example

Run this code

#include <iostream>
#include <string>
#include <cerrno>
#include <cwchar>
 
int main()
{
    const wchar_t* p = L"111.11 -2.22 0X1.BC70A3D70A3D7P+6  1.18973e+4932zzz";
    wchar_t* end;
    std::wcout << "Parsing L\"" << p << "\":\n";
    for (double f = std::wcstod(p, &end); p != end; f = std::wcstod(p, &end))
    {
        std::wcout << "'" << std::wstring(p, end-p) << "' -> ";
        p = end;
        if (errno == ERANGE){
            std::wcout << "range error, got ";
            errno = 0;
        }
        std::wcout << f << '\n';
    }
}

Output:

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

See also

strtofstrtodstrtold	converts a byte string to a floating point value (function)
C documentation for wcstof