Implement substr() function in C

Write an efficient function to implement substr() function in C. The substr() function returns the substring of a given string between two given indices.

The substr function prototype is: char* substr(const char *source, int m, int n)

It returns the substring of the source string starting at the position m and ending at position n-1.

#include <stdio.h>

#include <stdlib.h>

// Following function extracts characters present in `src`

// between `m` and `n` (excluding `n`)

char* substr(const char *src, int m, int n)

{

// get the length of the destination string

int len = n - m;

// allocate (len + 1) chars for destination (+1 for extra null character)

char *dest = (char*)malloc(sizeof(char) * (len + 1));

// extracts characters between m'th and n'th index from source string

// and copy them into the destination string

for (int i = m; i < n && (*(src + i) != '\0'); i++)

{

*dest = *(src + i);

dest++;

}

// null-terminate the destination string

*dest = '\0';

// return the destination string

return dest - len;

}

// Implement `substr()` function in C

int main()

{

char src[] = "substr function Implementation";

int m = 7;

int n = 12;

char* dest = substr(src, m, n);

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

return 0;

}

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Output:

funct

Following’s another implementation that uses C library’s strncpy() function: