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substr() in C++ - GeeksforGeeks

Last Updated : 19 May, 2025

In C++, the string substr() function is used to extract a substring from the given string. It generates a new string with its value initialized to a copy of a sub-string of the given string.

Example:

#include <iostream>
#include <string>
using namespace std;

int main() {
    
    // Take any string
    string s = "Geeks";

    // Extract two characters of s1 (starting
    // from index 3)
    string sub = s.substr(3, 2);

    cout << sub;
    return 0;
}

In the above example, we have extracted the last two characters from the string s and stored them in sub string using substr() function.

The std::string::substr() is the member function of string class defined inside <string> header file.

Parameters:

• pos: Index of the first character to be copied.
• len: Length of the sub-string.

Return Value:

• It returns a string object.

1. The index of the first character is 0 (not 1).
2. If pos is equal to the string length, the function returns an empty string.
3. If pos is greater than the string length, it throws out_of_range. If this happens, there are no changes in the string.
4. If the requested sub-string len is greater than the size of a string, then returned sub-string is [pos, size()).
5. If len is not passed as a parameter, then returned sub-string is [pos, size()).

The following examples illustrates the use of substr() function in C++:

In this example, a string and a character are given and you have to print the complete sub-string followed by the given character.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string s = "dog:cat";

    // Find position of ':' using find()
    int pos = s.find(":");

    // Extract substring after pos
    string sub = s.substr(pos + 1);
    cout << "Substring is: " << sub;
    return 0;
}

This example is a follow-up to the previous one, where we example, we print the complete substring up to a specific character.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string s = "dog:cat";

    // Find position of ':' using find()
    int pos = s.find(":");

    // Copy substring before pos
    // Extract everything before the ":" in the string
    // "dog:cat".
    string sub = s.substr(0, pos);
    cout << "Substring is: " << sub;

    return 0;
}

This example is a very famous interview question also. We need to write a program that will print all non-empty substrings of that given string.

#include <bits/stdc++.h>
using namespace std;

int main() {
    
    string s = "abcd";
    // subString(s, s.length());
    int n = s.length();
    
    // Logic to print all substring
    // using substr()
    for (int i = 0; i < n; i++)
        for (int len = 1; len <= n - i; len++)
            cout << s.substr(i, len) << endl;
    return 0;
}

a
ab
abc
abcd
b
bc
bcd
c
cd
d

Given an integer represented as a string, we need to get the sum of all possible substrings of this string.

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s = "1234";
    int res = 0;
    int n = s.length();
    for (int i = 0; i < n; i++) {
        for (int len = 1; len <= n - i; len++) {
            string sub = (s.substr(i, len));
            
            // Convert the substring into 
            // integer number
            int x = stoi(sub);
            res += x;
        }
    }
    cout << res;
    return 0;
}

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