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Create substring by given start, end index of a string | C ++ STL

In this article, we will learn how to create a substring by given start, end index of a string in C++ STL (Standard Template Library)? Here, we will use string header and its inbuilt function to implement the program.
Submitted by IncludeHelp, on August 22, 2018

Problem statement

Given a string, and we have to create a substring from a string, where start and end indexes are given.

Creating substring by given start, end index

To copy characters from a given start index to end index, we use substr() function, it is a library function, it is a library function of string header. It returns string object reference.

Syntax

string& substr(start_index, n);

Here,

• start_index is the starting index.
• n is the number of characters to be copied.

Here is an example with sample input and output:

Input:
str = "C++ programming language"
start = 2
end = 6

Function  call:
str2 = substring(start, (end-start))
//we have to access 4 characters from 2nd  index
//thus, (end-start) = (6-2) = 4

Output:
str1: "C++ programming language"
str2: "+ pr"

C++ program to create substring by given start, end index of a string

#include <iostream>
#include <string>

using namespace std;

int main() {
  // declare string and substring
  string str1 = "C++ programming language";
  string str2;

  // star and end index
  int start = 2;
  int end = 6;

  // copy charcters from 2 to 6 index
  str2 = str1.substr(start, (end - start));

  // print strings
  cout << "str1: " << str1 << endl;
  cout << "str2: " << str2 << endl;

  return 0;
}

Output

str1: C++ programming language
str2: + pr