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# Get a Substring in C

• Last Updated : 22 Dec, 2022

Given a string str and pos and len that defines the starting and the length of the subarray. The task is to generate a substring of size len starting from the index pos

A substring is a contiguous sequence of characters within a String.

Examples:

Input: Str =”the”, pos=1, len=2
Output:  “th”
Explanation: substrings will be: “”, “t”, “h”, “e”, “th”, “he”, “the”.

Input: Str =”geeks”, pos=3, length=3
Output: “eks”
Explanation: substrings are: “”, ” g”, “e”, “e”, “k”, “s”, “ge”, “ee”, “ek”, “ks”, “gee”, “eek”, “eks”, “geek”, “eeks”, “geeks”.

Approach: The problem can be solved following the below idea:

Create a character array and put the characters starting from pos to the character array to generate the substring.

Follow the below steps to implement the idea:

• Create a character array to store the substring.
• Iterate from the given position for the given length to generate the substring required.
• Then store each character in the character array and print the substring.

Follow the below illustration for a better understanding.

Illustration:

Consider a string str=”abcde” , pos = 2, len = 3.

=> At i = 2 our ans = “c”

=> At i = 3, the character is ‘d’.
Our ans = “cd”

=> At i = 4, the character is ‘e’.
Uur ans = “cde”.

Below is the implementation of the above approach.

## C

```// C implementation of code
#include <stdio.h>
#include <string.h>

// Function to get substr in C
void getString(int pos, int len, int c, char string[])
{

char substring;

while (c < len) {
substring = string[pos + c - 1];
c++;
}

substring = '\0';

// Print the result
printf(substring);
printf("\n");
return 0;
}

// Driver code
int main()
{

int pos, len, c = 0;

// Testcase1
char string = "geeksforgeeks";

// Initialize pos, len i.e., starting
// index and len upto which we have to
// get substring respectively.
pos = 6;
len = 5;
printf("String: %s ", string);
printf("\nsubstring is: ");

// Function call
getString(pos, len, c, string);

// Testcase2
char string2 = "abcde";
pos = 1;
len = 3;
c = 0;
printf("\nString: %s ", string2);
printf("\nsubstring is: ");

// Function call
getString(pos, len, c, string2);

return 0;
}```
Output

```String: geeksforgeeks
substring is: forge

String: abcde
substring is: abc
```

Time complexity: O(len)
Auxiliary space: O(len)

## Using strncpy() function in C

We can also use strncpy() function in C to copy the substring from a given input string. It takes 3 parameters which are the destination string, source string along with starting index and length of the substring which we need to copy.

Syntax:

strncpy(destination_string,input_string+pos,len);

Here pos is the starting index and len is the length of the substring which we want to copy.

Below is the code for the above approach.

## C

```// C implementation of code
#include <stdio.h>
#include <string.h>

// Driver code
int main()
{
int pos, len;

// Testcase1
char string = "geeksforgeeks";
char substring;

// Initialize pos, len i.e., starting
// index and len upto which we have to
// get substring respectively.
pos = 6;
len = 5;
printf("String: %s ", string);
printf("\nsubstring is: ");

// Using strncpy function to
// copy the substring
strncpy(substring,string+(pos-1),len);
printf(substring);

// Testcase2
char string2 = "abcde";
char substring2;

pos = 1;
len = 3;
printf("\nString: %s ", string2);
printf("\nsubstring is: ");

// Using strncpy function to
// copy the substring
strncpy(substring2,string2+(pos-1),len);
printf(substring2);
return 0;
}

// This code is contributed by Pushpesh Raj.
```
Output

```String: geeksforgeeks
substring is: forge
String: abcde
substring is: abc```

Time complexity: O(len)
Auxiliary space: O(len)

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