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

Difficulty Level : Medium
Last Updated : 29 Oct, 2018

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 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 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.

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 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 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.

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 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:

Example 2:

// 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

This article is contributed by Shivani Ghughtyal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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