There are situations, where we need to convert textual data into numerical values for various calculations. In this article, we will learn how to convert strings to double in C++.
Methods to Convert String to Double
We can convert String to Double in C++ using the following methods:
- Using stod() Function
- Using stold() Function
- Using atof() Function
Let's discuss each of these methods in detail.
1. Using stod() Function
In C++, the stod() function performs a string to double conversion. It is a library function defined inside <string.h> header file.
Syntax
double stod(const string& 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
- Converted double value.
C++ Program to Convert String to Double Using stod() Function
// C++ program to convert string
// to double using stod()
#include <iostream>
using namespace std;
// Driver code
int main()
{
char s1[] = "14.25";
char s2[] = "34.87";
double n1 = stod(s1);
double n2 = stod(s2);
double res = n1 + n2;
cout << res;
return 0;
}
Output
49.12
Complexity Analysis
- Time complexity: O(1)
- Auxiliary Space: O(1)
2. Using stold() Function
In C++, the stold() function performs a string to long double conversion. Like stod() function, this function is also defined inside <string.h> header file.
Syntax
long double stold(const string& 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
- Converted long double value.
C++ Program to Convert String to Long Double Using stold() Function
// C++ program to convert string
// to long double using stold()
#include <iostream>
using namespace std;
// Driver code
int main()
{
char s1[] = "14.25";
char s2[] = "34.87";
long double n1 = stold(s1);
long double n2 = stold(s2);
long double res = n1 + n2;
cout << res;
return 0;
}
Output
49.12
Complexity Analysis
- Time complexity: O(1)
- Auxiliary Space: O(1)
3. Using atof() Function
In C++, the atof() method translates a string's contents as a floating-point integer and returns its value as a double. It is declared inside <cstdlib> header file.
Syntax
double atof (const char * str)
Parameters
- The function accepts a single mandatory parameter str which is the string representation of a floating-point number.
Return Value
- Converted long double value.
C++ Program to Convert String to Double Using atof() Function
// C++ program to convert string
// to double using atof()
#include <iostream>
using namespace std;
// Driver code
int main()
{
char s[] = "14.25";
double num = atof(s);
cout << num;
return 0;
}
Output
14.25
Complexity Analysis
- Time complexity: O(1)
- Auxiliary Space: O(1)