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Difference between revisions of "cpp/string/basic string/stof"

From cppreference.com
< cpp‎ | string‎ | basic string
(Added LWG issue #2009 DR (part 3/3).)
 
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{{cpp/title| stof | stod | stold}}
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{{cpp/title|stof|stod|stold}}
 
{{cpp/string/basic_string/navbar}}
 
{{cpp/string/basic_string/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
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{{dcl header | string}}
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{{dcl header|string}}
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{{dcl | num=1 | since=c++11 | 1=
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{{dcl|num=1|since=c++11|1=
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float      stof( const std::string& str, size_t *pos = 0 );
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float      stof ( const std::string& str, std::size_t* pos = nullptr );
 
}}
 
}}
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{{dcl | num=2 | since=c++11 | 1=
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{{dcl|num=2|since=c++11|1=
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double      stod( const std::string& str, size_t *pos = 0 );
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float      stof ( const std::wstring& str, std::size_t* pos = nullptr );
 
}}
 
}}
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{{dcl | num=3 | since=c++11 | 1=
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{{dcl|num=3|since=c++11|1=
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long double stold( const std::string& str, size_t *pos = 0 );
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double      stod ( const std::string& str, std::size_t* pos = nullptr );
 +
}}
 +
{{dcl|num=4|since=c++11|1=
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double      stod ( const std::wstring& str, std::size_t* pos = nullptr );
 +
}}
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{{dcl|num=5|since=c++11|1=
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long double stold( const std::string& str, std::size_t* pos = nullptr );
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}}
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{{dcl|num=6|since=c++11|1=
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long double stold( const std::wstring& str, std::size_t* pos = nullptr );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
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Interprets a floating point value in a string {{tt|str}}.  
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Interprets a floating point value in a string {{c|str}}.  
  
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@1@ calls {{c|std::strtod(str.c_str(), pos)}}
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Let {{c|ptr}} be an internal (to the conversion functions) pointer of type {{c/core|char*}} {{v|1,3,5}} or {{c/core|wchar_t*}} {{v|2,4,6}}, accordingly.
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@2@ calls {{c|std::strtod(str.c_str(), pos)}}
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−
@3@ calls {{c|std::strtold(str.c_str(), pos)}}
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@1@ Calls {{c|std::strtof(str.c_str(), &ptr)}}.
 +
@2@ Calls {{c|std::wcstof(str.c_str(), &ptr)}}.
 +
@3@ Calls {{c|std::strtod(str.c_str(), &ptr)}}.
 +
@4@ Calls {{c|std::wcstod(str.c_str(), &ptr)}}.
 +
@5@ Calls {{c|std::strtold(str.c_str(), &ptr)}}.
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@6@ Calls {{c|std::wcstold(str.c_str(), &ptr)}}.
  
 
{{cpp/string/cvt str2float}}
 
{{cpp/string/cvt str2float}}
  
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The index of the first unconverted character is stored in {{tt|pos}}. If {{lc|NULL}} is passed as {{tt|pos}}, it is ignored.
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If {{c|pos}} is not a null pointer, then {{c|ptr}} will receive the address of the first unconverted character in {{c|str.c_str()}}, and the index of that character will be calculated and stored in {{c|*pos}}, giving the number of characters that were processed by the conversion.
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
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{{par | str | the string to convert}}
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{{par|str|the string to convert}}
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{{par | pos | address of integer to store the index of the first unconverted character}}
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{{par|pos|address of an integer to store the number of characters processed}}
 
{{par end}}
 
{{par end}}
  
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===Exceptions===
 
===Exceptions===
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{{lc|std::invalid_argument}} if no conversion could be performed
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{{lc|std::invalid_argument}} if no conversion could be performed.
 +
 
 +
{{lc|std::out_of_range}} if the converted value would fall out of the range of the result type or if the underlying function ({{lc|std::strtof}}, {{lc|std::strtod}} or {{lc|std::strtold}}) sets {{lc|errno}} to {{lc|ERANGE}}.
 +
 
 +
===Example===
 +
{{example}}
  
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{{lc|std::out_of_range}} if the converted value would fall out of the range of the result type or if the underlying function ({{tt|strtod}} or {{tt|strtold}}) sets {{c|errno}} to {{c|ERANGE}}.
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===Defect reports===
 +
{{dr list begin}}
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{{dr list item|wg=lwg|dr=2009|std=C++11|before={{lc|std::out_of_range}} would not be thrown if the converted<br>value would fall out of the range of the result type|after=will throw}}
 +
{{dr list item|wg=lwg|dr=2403|std=C++11|before={{tt|stof}} called {{lc|std::strtod}} or {{lc|std::wcstod}}|after={{tt|stof}} calls {{lc|std::strtof}} or {{lc|std::wcstof}}}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
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{{dsc inc | cpp/string/basic_string/dsc stol}}
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{{dsc inc|cpp/string/basic_string/dsc stol}}
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{{dsc inc | cpp/string/basic_string/dsc stoul}}
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{{dsc inc|cpp/string/basic_string/dsc stoul}}
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{{dsc inc|cpp/utility/dsc from_chars}}  
 
{{dsc end}}
 
{{dsc end}}
  
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[[de:cpp/string/basic string/stof]]
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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[[es:cpp/string/basic string/stof]]
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[[fr:cpp/string/basic string/stof]]
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[[it:cpp/string/basic string/stof]]
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[[ja:cpp/string/basic string/stof]]
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[[pt:cpp/string/basic string/stof]]
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[[ru:cpp/string/basic string/stof]]
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[[zh:cpp/string/basic string/stof]]
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Latest revision as of 19:31, 7 August 2023

 
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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 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.

Contents

[edit] Parameters

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

[edit] Return value

The string converted to the specified floating point type.

[edit] 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 (std::strtof, std::strtod or std::strtold) sets errno to ERANGE.

[edit] Example

This section is incomplete
Reason: no example

[edit] 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 2009 C++11 std::out_of_range would not be thrown if the converted
value would fall out of the range of the result type 		will throw
LWG 2403 C++11 stof called std::strtod or std::wcstod stof calls std::strtof or std::wcstof

[edit] See also

(C++11)(C++11)(C++11)
 converts a string to a signed integer
(function) [edit]
(C++11)(C++11)
 converts a string to an unsigned integer
(function) [edit]
(C++17)
 converts a character sequence to an integer or floating-point value
(function) [edit]
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