Substring in C++

Difficulty Level : Easy
Last Updated : 05 May, 2018

In C++, std::substr() is a predefined function used for string handling. string.h is the header file required for string functions.

This function takes two values pos and len as an argument and returns a newly constructed string object with its value initialized to a copy of a sub-string of this object. Copying of string start from pos and done till pos+len means [pos, pos+len).

Important points:

The index of the first character is 0 (not 1).
If pos is equal to the string length, the function returns an empty string.
If pos is greater than the string length, it throws out_of_range. If this happen, there are no changes in the string.
If for the requested sub-string len is greater than size of string, then returned sub-string is [pos, size()).

Syntax:

string substr (size_t pos, size_t len) const;
Parameters:
pos: Position of the first character to be copied.
len: Length of the sub-string.
size_t: It is an unsigned integral type.

Return value: It returns a string object.

// CPP program to illustrate substr()
#include <string.h>
#include <iostream>
using namespace std;
  
int main()
{
    // Take any string
    string s1 = "Geeks";
  
    // Copy three characters of s1 (starting 
    // from position 1)
    string r = s1.substr(1, 3);
  
    // prints the result
    cout << "String is: " << r;
  
    return 0;
}

Output:

String is: eek

Applications :

How to get sub-string after a character?
In this a string and a character is given and you have to print the sub-string followed by the given character.
Extract everything after the “:” in the string “dog:cat”.

// CPP program to illustrate substr()
#include <string.h>
#include <iostream>
using namespace std;
  
int main()
{
    // Take any string
    string s = "dog:cat";
  
    // Find position of ':' using find()
    int pos = s.find(":");
  
    // Copy substring after pos
    string sub = s.substr(pos + 1);
  
    // prints the result
    cout << "String is: " << sub;
  
    return 0;
}

Output:

String is: cat

Print all substrings of a given string
Sum of all substrings of a string representing a number
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