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std::stof, std::stod, std::stold

Defined in header `<string>`
float stof( const std::string& str, std::size_t* pos = nullptr );	(1)	(since C++11)
float stof( const std::wstring& str, std::size_t* pos = nullptr );	(2)	(since C++11)
double stod( const std::string& str, std::size_t* pos = nullptr );	(3)	(since C++11)
double stod( const std::wstring& str, std::size_t* pos = nullptr );	(4)	(since C++11)
long double stold( const std::string& str, std::size_t* pos = nullptr );	(5)	(since C++11)
long double stold( const std::wstring& str, std::size_t* pos = nullptr );	(6)	(since C++11)

Interprets a floating point value in a string str.

Let ptr be an internal (to the conversion functions) pointer of type char* (1,3,5) or wchar_t* (2,4,6), accordingly.

1) Calls std::strtof(str.c_str(), &ptr).

2) Calls std::wcstof(str.c_str(), &ptr).

3) Calls std::strtod(str.c_str(), &ptr).

4) Calls std::wcstod(str.c_str(), &ptr).

5) Calls std::strtold(str.c_str(), &ptr).

6) Calls std::wcstold(str.c_str(), &ptr).

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 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.

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

If pos is not a null pointer, then the pointer ptr will receive the address of the first unconverted character in str.c_str(), and the index of that character will be calculated and stored in *pos, giving the number of characters that were processed by the conversion.

Parameters

str	-	the string to convert
pos	-	address of an integer to store the number of characters processed

Return value

The string converted to the specified floating point type.

Exceptions

std::invalid_argument if no conversion could be performed.

std::out_of_range if the converted value would fall out of the range of the result type or if the underlying function (strtof, strtod or strtold) sets errno to ERANGE.

Example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2403	C++11	`stof` called `std::strtod` or `std::wcstod`	`stof` calls `std::strtof` or `std::wcstof`