How to Extract a Substring From a String in C

In this tutorial, we are going to see how to extract a substring from a string in C. In the following program we implement a defined function named extract(). This function takes four arguments, the source string, substring, start index(from) and end index(to), and will return either 0 (in case of successful execution) or 1 (in case of failed execution).
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How to Extract a Substring From a String in C

#include <stdio.h>
#include <string.h>

int extract(int from, int to, char *string, char *subString)
{
  int i=0, j=0;
  //get the length of the string.
  int length = strlen(string);
  
  if( from > length || from < 0 ){
    printf("The index 'from' is invalid\n");
    return 1;
  }
  if( to > length ){
    printf("The index 'to' is invalid\n");
    return 1;
  }  
  for( i = from, j = 0; i <= to; i++, j++){
    subString[j] = string[i];
  }  
  return 0;  
}

int main()
{
  char string[100];
  char subString[50];
  int from,to;
  
  printf("Enter a string: ");
  fgets(string,100,stdin);
  printf("Enter the index 'from': ");
  scanf("%d",&from);
  printf("Enter the index 'to': ");
  scanf("%d",&to);  
  
  printf("The string is : %s",string);
  
  if( extract(from, to, string, subString) == 0 )
      printf("The sub-string is : %s", subString);
    else
        printf("ERROR!\n");
  
  return 0;
}

Output:

Enter a string: Welcome to StackHowTo
Enter the index 'from': 11
Enter the index 'to': 20
The string is : Welcome to StackHowTo
The sub-string is : StackHowTo

 

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