Localization library | |||||||||||||||||||||||||
Regular expressions library(C++11) | |||||||||||||||||||||||||
Formatting library(C++20) | |||||||||||||||||||||||||
Null-terminated sequence utilities | |||||||||||||||||||||||||
Byte strings | |||||||||||||||||||||||||
Multibyte strings | |||||||||||||||||||||||||
Wide strings | |||||||||||||||||||||||||
Primitive numeric conversions | |||||||||||||||||||||||||
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Text encoding identifications | |||||||||||||||||||||||||
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Functions | ||||||||||||||||||||||||||||||||||||
Character classification | ||||||||||||||||||||||||||||||||||||
Character manipulation | ||||||||||||||||||||||||||||||||||||
Conversions to numeric formats | ||||||||||||||||||||||||||||||||||||
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String manipulation | ||||||||||||||||||||||||||||||||||||
String examination | ||||||||||||||||||||||||||||||||||||
Character array functions | ||||||||||||||||||||||||||||||||||||
Miscellaneous | ||||||||||||||||||||||||||||||||||||
Defined in header <cstdlib> | ||
float strtof(constchar* str,char** str_end); | (1) | (since C++11) |
double strtod(constchar* str,char** str_end); | (2) | |
longdouble strtold(constchar* str,char** str_end); | (3) | (since C++11) |
Interprets a floating point value in a byte string pointed to bystr.
Function discards any whitespace characters (as determined bystd::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:
e
orE
followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base10)
| (since C++11) |
The functions sets the pointer pointed to bystr_end to point to the character past the last character interpreted. Ifstr_end is a null pointer, it is ignored.
Contents |
str | - | pointer to the null-terminated byte string to be interpreted |
str_end | - | pointer to a pointer to character. |
Floating point value corresponding to the contents ofstr on success. If the converted value falls out of range of corresponding return type, range error occurs andHUGE_VAL,HUGE_VALF orHUGE_VALL is returned. If no conversion can be performed,0 is returned and*str_end is set tostr.
#include <cerrno>#include <clocale>#include <cstdlib>#include <iostream>#include <string> int main(){constchar* p="111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz";char* end{};std::cout<<"Parsing\""<< p<<"\":\n";errno=0;for(double f= std::strtod(p,&end); p!= end; f= std::strtod(p,&end)){std::cout<<" '"<<std::string(p, end- p)<<"' -> "; p= end;if(errno==ERANGE){std::cout<<"range error, got ";errno=0;}std::cout<< f<<'\n';} if(std::setlocale(LC_NUMERIC,"de_DE.utf8")){std::cout<<"With de_DE.utf8 locale:\n";std::cout<<" '123.45' -> "<< std::strtod("123.45",0)<<'\n';std::cout<<" '123,45' -> "<< std::strtod("123,45",0)<<'\n';}}
Possible output:
Parsing "111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz": '111.11' -> 111.11 ' -2.22' -> -2.22 ' 0X1.BC70A3D70A3D7P+6' -> 111.11 ' -Inf' -> -inf ' 1.18973e+4932' -> range error, got infWith de_DE.utf8 locale: '123.45' -> 123 '123,45' -> 123.45
converts a byte string to a floating point value (function)[edit] | |
converts a wide string to a floating-point value (function)[edit] | |
(C++17) | converts a character sequence to an integer or floating-point value (function)[edit] |
C documentation forstrtof,strtod,strtold |