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

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< cpp‎ | string‎ | basic string

Defined in header `<string>` |  |
float stof( const std::string& str, std::size_t* pos = 0 ); float stof( const std::wstring& str, std::size_t* pos = 0 ); | (1) | (since C++11)
double stod( const std::string& str, std::size_t* pos = 0 ); double stod( const std::wstring& str, std::size_t* pos = 0 ); | (2) | (since C++11)
long double stold( const std::string& str, std::size_t* pos = 0 ); long double stold( const std::wstring& str, std::size_t* pos = 0 ); | (3) | (since C++11)

Interprets a floating point value in a string `str`.

1) calls std::strtod(str.c_str(), &ptr) or std::wcstod(str.c_str(), &ptr) | (until C++17)
1) calls std::strtof(str.c_str(), &ptr) or std::wcstof(str.c_str(), &ptr) | (since C++17)

2) calls std::strtod(str.c_str(), &ptr) or std::wcstod(str.c_str(), &ptr)
3) calls std::strtold(str.c_str(), &ptr) or 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)

- 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

If `pos` is not a null pointer, then a pointer `ptr`, internal to the conversion functions, 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`, (since C++17)`strtod` or `strtold`) sets errno to ERANGE.

### See also

stoi stol stoll (C++11)(C++11)(C++11) | converts a string to a signed integer (function)
stoul stoull (C++11)(C++11) | converts a string to an unsigned integer (function)
from_chars (C++17) | converts a character sequence to an integer or floating-point value (function)

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