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

From cppreference.com
< cpp‎ | string‎ | byte
m (Shorten template names. Use {{lc}} where appropriate.)
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{{cpp/title| strtof | strtod | strtold}}
 
{{cpp/title| strtof | strtod | strtold}}
 
{{cpp/string/byte/navbar}}
 
{{cpp/string/byte/navbar}}
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{{ddcl list begin}}
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{{dcl begin}}
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{{ddcl list header | cstdlib}}
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{{dcl header | cstdlib}}
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{{ddcl list item | notes={{mark since c++11}} |
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{{dcl | notes={{mark since c++11}} |
 
float      strtof( const char* str, char** str_end );           
 
float      strtof( const char* str, char** str_end );           
 
}}
 
}}
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{{ddcl list item |  
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{{dcl |  
 
double      strtod( const char* str, char** str_end );
 
double      strtod( const char* str, char** str_end );
 
}}
 
}}
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{{ddcl list item | notes={{mark since c++11}} |
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{{dcl | notes={{mark since c++11}} |
 
long double strtold( const char* str, char** str_end );
 
long double strtold( const char* str, char** str_end );
 
}}
 
}}
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{{ddcl list end}}
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{{dcl end}}
  
 
Interprets a floating point value in a byte string pointed to by {{tt|str}}.
 
Interprets a floating point value in a byte string pointed to by {{tt|str}}.
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{{cpp/string/cvt str2float}}
 
{{cpp/string/cvt str2float}}
  
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The functions sets the pointer pointed to by {{tt|str_end}} to point to the character past the last character interpreted. If {{tt|str_end}} is {{c|NULL}}, it is ignored.
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The functions sets the pointer pointed to by {{tt|str_end}} to point to the character past the last character interpreted. If {{tt|str_end}} is {{lc|NULL}}, it is ignored.
  
 
===Parameters===
 
===Parameters===
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{{param list begin}}
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{{par begin}}
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{{param list item | str | pointer to the null-terminated byte string to be interpreted}}
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{{par | str | pointer to the null-terminated byte string to be interpreted}}
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{{param list item | str_end | pointer to a pointer to character.}}
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{{par | str_end | pointer to a pointer to character.}}
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{{param list end}}
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{{par end}}
  
 
===Return value===
 
===Return value===
−
Floating point value corresponding to the contents of {{tt|str}} on success. If the converted value falls out of range of corresponding return type, range error occurs and {{c|HUGE_VAL}}, {{c|HUGE_VALF}} or {{c|HUGE_VALL}} is returned. If no conversion can be performed, {{c|0}} is returned.
+
Floating point value corresponding to the contents of {{tt|str}} on success. If the converted value falls out of range of corresponding return type, range error occurs and {{lc|HUGE_VAL}}, {{lc|HUGE_VALF}} or {{lc|HUGE_VALL}} is returned. If no conversion can be performed, {{c|0}} is returned.
  
 
===Example===
 
===Example===
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===See also===
 
===See also===
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{{dcl list begin}}
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{{dsc begin}}
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{{dcl list template | cpp/string/byte/dcl list atof}}
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{{dsc inc | cpp/string/byte/dcl list atof}}
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{{dcl list see c | c/string/byte/strtof | strtof | strtod | strtold}}
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{{dsc see c | c/string/byte/strtof | strtof | strtod | strtold}}
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{{dcl list end}}
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{{dsc end}}
  
 
[[de:cpp/string/byte/strtof]]
 
[[de:cpp/string/byte/strtof]]

Revision as of 19:56, 31 May 2013

 
C++
 
Strings library
 
Null-terminated byte strings
Functions
Character manipulation
Conversions to numeric formats
(C++11)
strtofstrtodstrtold
(C++11)(C++11)
(C++11)(C++11)
String manipulation
String examination
Memory manipulation
Miscellaneous
 
Defined in header <cstdlib>
float       strtof( const char* str, char** str_end );
 (since C++11)
double      strtod( const char* str, char** str_end );
long double strtold( const char* str, char** str_end );
 (since C++11)

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

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is NULL, it is ignored.

Contents

Parameters

str - pointer to the null-terminated byte string to be interpreted
str_end - pointer to a pointer to character.

Return value

Floating point value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, ​0​ is returned.

Example

Run this code
#include <cstdlib>
#include <iostream>
 
int main()
{
    std::cout << std::strtod("0.0000000123", nullptr) << "\n";
 
    // the second arg of strto* is non-const. We must copy the string
    char src[] = "0.012  15e16 -0x1afp-2 inF Nan";
    char* c = src;
 
    std::cout << std::strtod(c, &c) << "\n";
    std::cout << std::strtod(c, &c) << "\n";
    std::cout << std::strtod(c, &c) << "\n";
    std::cout << std::strtod(c, &c) << "\n";
    std::cout << std::strtod(c, &c) << "\n";
}

Output: 

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

See also

Template:cpp/string/byte/dcl list atof
C documentation for strtof, strtod, strtold
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