C++ String Substring Searching

Introduction

To find a substring in a string, we use the .find() member function.

It searches for the substring in a string.

If the substring is found, the function returns the position of the first found substring.

This position is the position of a character where the substring starts in the main string.

If the substring is not found, the function returns a value that is std::string::npos.

The function itself is of type std::string::size_type.

To find a substring "Hello" inside the "This is a Hello World string" string, we write: 

#include <iostream> 
#include <string> 

int main() //from   ww  w.j  av a2s .co m
{ 
    std::string s = "This is a Hello World string."; 
    std::string stringtofind = "Hello"; 
    std::string::size_type found = s.find(stringtofind); 
    if (found != std::string::npos) 
    { 
        std::cout << "Substring found at position: " << found; 
    } 
    else 
    { 
        std::cout << "The substring is not found."; 
    } 
}

Here we have the main string and a substring we want to find.

We supply the substring to the .find() function as an argument.

We store the function's return value to a variable found.

Then we check the value of this variable.

If the value is not equal to std::string::npos, the substring was found.

We print the message and the position of a character in the main string, where our substring was found




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