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

From cppreference.com
< cpp‎ | string‎ | basic string
m (seealso from_chars)
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Interprets a floating point value in a string {{tt|str}}.  
 
Interprets a floating point value in a string {{tt|str}}.  
  
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{{rev begin}}
 
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{{rev|until=c++17|
 
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@1@ calls {{c|std::strtod(str.c_str(), &ptr)}} or {{c|std::wcstod(str.c_str(), &ptr)}}
 
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}}
 
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{{rev|since=c++17|
 
 
@1@ calls {{c|std::strtof(str.c_str(), &ptr)}} or {{c|std::wcstof(str.c_str(), &ptr)}}
 
@1@ calls {{c|std::strtof(str.c_str(), &ptr)}} or {{c|std::wcstof(str.c_str(), &ptr)}}
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}}
 
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{{rev end}}
 
 
@2@ calls {{c|std::strtod(str.c_str(), &ptr)}} or {{c|std::wcstod(str.c_str(), &ptr)}}
 
@2@ calls {{c|std::strtod(str.c_str(), &ptr)}} or {{c|std::wcstod(str.c_str(), &ptr)}}
 
@3@ calls {{c|std::strtold(str.c_str(), &ptr)}} or {{c|std::wcstold(str.c_str(), &ptr)}}
 
@3@ calls {{c|std::strtold(str.c_str(), &ptr)}} or {{c|std::wcstold(str.c_str(), &ptr)}}
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{{lc|std::invalid_argument}} if no conversion could be performed
 
{{lc|std::invalid_argument}} if no conversion could be performed
  
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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 ({{rev inl|since=c++17|{{tt|strtof}}, }}{{tt|strtod}} or {{tt|strtold}}) sets {{c|errno}} to {{c|ERANGE}}.
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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|strtof}}, {{tt|strtod}} or {{tt|strtold}}) sets {{c|errno}} to {{c|ERANGE}}.
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===Defect reports===
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{{dr list begin}}
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{{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}}}}
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{{dr list end}}
  
 
===See also===
 
===See also===
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Revision as of 00:33, 13 June 2020

 
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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::strtof(str.c_str(), &ptr) or std::wcstof(str.c_str(), &ptr)
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 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 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.

Contents

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.

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

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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