Check if Char Array Starts with a string in C++

This tutorial will discuss about a unique way to check if char array starts with a string.

To check if a char array starts with another string or char array, we can follow the following steps,

• Get the number of characters in first char array.
• Get the number of characters in second char array.
• Make sure that the number of characters in first char array is either equal to or greater than the number of characters in second char array.
• Use the strncmp() function to compare the first N characters of both the char arrays, where N is the number of characters in the second char array.
• If “strncmp()” returns 0, then it means that the string in first char array starts with the string in the second char array.

Let’s see the complete example,

#include <iostream>
#include <string.h>

// Check if a char array contains a character
bool startWith(
        const char * arr,
        const char* substring)
{
    bool result = false;

    // get number of characters in substring
    size_t subStrLen = strlen(substring) ;

    // get number of characters in char array string
    size_t mainStrLen = strlen(arr);

    // Check if char array starts with the given substring
    if( mainStrLen >= subStrLen &&
        strncmp(arr, substring, subStrLen) == 0)
    {
        result = true;
    }

    return result;
}

int main()
{

    char mainStr[50] = "This is a sample text";
    char subString[50] = "This";

    // Check if Char Array starts with a substring
    if(startWith(mainStr, subString) )
    {
        std::cout<<"Char Array starts with a substring \n";
    }
    else
    {
        std::cout<<"Char Array does not starts with a substring \n";
    }
    return 0;
}

Output :

Char Array starts with a substring

Summary

Today we learned about several ways to check if char array starts with a string. Thanks.