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std::stod, std::stof, std::stold in C++

Last Updated : 29 Oct, 2018
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  1. std::stod() : It convert string into double. Syntax: 
    double stod( const std::string& str, std::size_t* pos = 0 );
double stod( const std::wstring& str, std::size_t* pos = 0 );
Return Value: return a value of type double
Parameters
str : the string to convert
pos : address of an integer to store the 
number of characters processed. This parameter can also be 
a null pointer, in which case it is not used.
    CPP 
    // CPP program to illustrate
// std::stod()
#include <string>
#include <iostream>

int main(void)

{
    std::string str = "y=4.4786754x+5.6";

    double y, x, a, b;
    y = 0;
    x = 0;

    // offset will be set to the length of 
    // characters of the "value" - 1.
    std::size_t offset = 0;

    a = std::stod(&str[2], &offset);
    b = std::stod(&str[offset + 3]);

    std::cout << b;
    return 0;
}
    Output: 
    5.6
    Another Example : CPP 
    // CPP program to illustrate
// std::stod()
#include <iostream>
#include <string>
using namespace std;
int main()
{

    string b = "5";
    double a = stod(b);
    int c = stoi(b);
    cout << b << " " << a << " " << c << endl;
}
    Output: 
    5 5 5
    If conversion is not performed, an invalid_argument exception is thrown. If the value read is out of the range of representable values by a double an out_of_range exception is thrown. An invalid idx causes undefined behavior.
  2. std::stof : It convert string into float. Syntax: 
    float stof( const string& str, size_t* pos = 0 );
float stof( const wstring& str, size_t* pos = 0 );
Parameters
str : the string to convert
pos : address of an integer to store the number of characters processed
This parameter can also be a null pointer, in which case it is not used.
Return value: it returns value of type float.
    Example 1: CPP 
    // CPP program to illustrate
// std::stof()
#include <iostream>
#include <string>
int main()
{
    std::string x;
    x = "20";
    float y = std::stof(x) + 2.5;
    std::cout << y;
    return 0;
}
    Output: 
    22.5
    Example 2: CPP 
    // CPP program to illustrate
// std::stof()
#include <iostream>
#include <string>
int main()
{
    std::string str = "5000.5";
    float x = std::stof(str);
    std::cout << x;
    return 0;
}
    Output: 
    5000.5
    If no conversion could be performed, an invalid_argument exception is thrown.
  3. std::stold : It convert string into long double. Syntax: 
    long double stold( const string& str, size_t *pos = 0 );
long double stold (const wstring& str, size_t* pos = 0);
Parameters : 
str : the string to convert
pos : address of integer to store the index of the first unconverted character.
This parameter can also be a null pointer, in which case it is not used.
Return value : it returns value of type long double.
    Examples 1: CPP 
    // CPP program to illustrate
// std::stold()
#include <iostream>
#include <string>
int main()
{
    std::string str = "500087";
    long double x = std::stold(str);
    std::cout << x;
    return 0;
}
    Output: 
    500087
    Example 2: CPP 
    // CPP program to illustrate
// std::stold()
#include <iostream>
#include <string>
int main()
{
    std::string x;
    x = "2075";
    long double y = std::stof(x) + 2.5;
    std::cout << y;
    return 0;
}
    Output: 
    2077.5

S

Shivani Ghughtyal
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