Implement substring function in C

Write an efficient function to implement substring function in C. The substring function returns the substring of a given string containing n characters starting from the given index.

The prototype of the substring() function is:

char* substring(char *destination, const char *source, int beg, int n)

The substring() function returns the substring of the source string starting at the position specified in the third argument and the length specified in the fourth argument of the function.

The following code implements the substring() function, which extracts n characters from the source string starting from the beg index and returns it.

C

#include <stdio.h>

// Function to implement substring function in C

char* substring(char *destination, const char *source, int beg, int n)

{

// extracts `n` characters from the source string starting from `beg` index

// and copy them into the destination string

while (n > 0)

{

*destination = *(source + beg);

destination++;

source++;

n--;

}

// null terminate destination string

*destination = '\0';

// return the destination string

return destination;

}

// Implement `substring()` function in C

int main()

{

char source[] = "Techie Delight – Ace the Technical Interviews";

char destination[25];

int start = 7;

int len = 7;

substring(destination, source, start, len);

printf("%s\n", destination);

return 0;

}

Download Run Code

Output:

Delight

Here’s another version that uses the strncpy() function provided by the C library:

C