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Difference between revisions of "cpp/string/byte/atof"

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< cpp‎ | string‎ | byte
 
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{{cpp/title| atof}}
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{{cpp/title|atof}}
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{{cpp/string/narrow/sidebar}}
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{{cpp/string/byte/navbar}}
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{{ddcl | header=cstdlib |
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{{ddcl|header=cstdlib|
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double atof( const char *str );
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double atof( const char* str );
 
}}
 
}}
  
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Interprets an floating point value in a character string pointed to by {{tt|str}}.
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Interprets a floating point value in a byte string pointed to by {{c|str}}.
  
 
{{cpp/string/cvt str2float}}
 
{{cpp/string/cvt str2float}}
  
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<!-- ======== -->
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===Parameters===
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{{params}}
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{{par begin}}
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{{param list begin}}
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{{par|str|pointer to the null-terminated byte string to be interpreted}}
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{{param list item | str | pointer to the null-terminated character string to be interpreted}}
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{{par end}}
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{{param list end}}
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<!-- ======== -->
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===Return value===
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{{returns}}
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{{c|double}} value corresponding to the contents of {{c|str}} on success. If the converted value falls out of range of the return type, the return value is undefined. If no conversion can be performed, {{c|0.0}} is returned.
  
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{{cpp|double}} value corresponding to the contents of {{tt|str}} on success. If the converted value falls out of range of corresponding return type, {{tt|HUGE_VAL}} is returned. If no conversion can be performed, {{cpp|0.0}} is returned.
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===Example===
 +
{{example
 +
|code=
 +
#include <cstdlib>
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#include <iostream>
 +
 +
int main()
 +
{
 +
    std::cout << std::atof("0.0000000123") << '\n'
 +
              << std::atof("0.012") << '\n'
 +
              << std::atof("15e16") << '\n'
 +
              << std::atof("-0x1afp-2") << '\n'
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              << std::atof("inF") << '\n'
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              << std::atof("Nan") << '\n'
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              << std::atof("invalid") << '\n';
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}
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|output=
 +
1.23e-08
 +
0.012
 +
1.5e+17
 +
-107.75
 +
inf
 +
nan
 +
0
 +
}}
  
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{{todo | reason=fix links to limits}}
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===See also===
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{{dsc begin}}
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<!-- ======== -->
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{{dsc inc|cpp/string/basic_string/dsc stof}}
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{{example}}
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{{dsc inc|cpp/string/byte/dsc strtof}}
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{{example cpp
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{{dsc inc|cpp/utility/dsc from_chars}}
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|
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{{dsc inc|cpp/string/byte/dsc atoi}}
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| code=
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{{dsc see c|c/string/byte/atof}}
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| output=
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{{dsc end}}
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}}
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<!-- ======== -->
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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{{see also}}
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{{dcl list begin}}
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{{dcl list template | cpp/string/narrow/dcl list strtof}}
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{{dcl list end}}
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Latest revision as of 08:28, 5 June 2023

 
C++
 
Strings library
 
Null-terminated byte strings
Functions
Character manipulation
Conversions to numeric formats
atof
(C++11)
(C++11)

(C++11)
(C++11)(C++11)
(C++11)(C++11)
String manipulation
String examination
Memory manipulation
Miscellaneous
 
Defined in header <cstdlib>
double atof( const char* str );

Interprets a floating point value in a byte 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 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.
(since C++11)
  • any other expression that may be accepted by the currently installed C locale

Contents

[edit] Parameters

str - pointer to the null-terminated byte string to be interpreted

[edit] Return value

double value corresponding to the contents of str on success. If the converted value falls out of range of the return type, the return value is undefined. If no conversion can be performed, 0.0 is returned.

[edit] Example

Run this code
#include <cstdlib>
#include <iostream>
 
int main()
{
    std::cout << std::atof("0.0000000123") << '\n'
              << std::atof("0.012") << '\n'
              << std::atof("15e16") << '\n'
              << std::atof("-0x1afp-2") << '\n'
              << std::atof("inF") << '\n'
              << std::atof("Nan") << '\n'
              << std::atof("invalid") << '\n';
}

Output: 

1.23e-08
0.012
1.5e+17
-107.75
inf
nan
0

[edit] See also

(C++11)(C++11)(C++11)
 converts a string to a floating point value
(function) [edit]
converts a byte string to a floating-point value
(function) [edit]
(C++17)
 converts a character sequence to an integer or floating-point value
(function) [edit]
(C++11)
 converts a byte string to an integer value
(function) [edit]
C documentation for atof
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