Substring in c programming, c substring

Substring in c programming: c programming code to find a substring from a given string and for all substrings of a string, For example substrings of string "the" are "t", "th", "the", "h", "he" and "e" to find substring we create our own c substring function which returns a pointer to string. String address, length of substring required and position from where to extract substring are the three arguments passed to function. String.h does not contain any library function to directly find substring.

C substring code

#include <stdio.h>
 
int main() 
{
   char string[1000], sub[1000];
   int position, length, c = 0;
 
   printf("Input a string\n");
   gets(string);
 
   printf("Enter the position and length of substring\n");
   scanf("%d%d", &position, &length);
 
   while (c < length) {
      sub[c] = string[position+c-1];
      c++;
   }
   sub[c] = '\0';
 
   printf("Required substring is \"%s\"\n", sub);
 
   return 0;
}

C substring program output:

C substring program using function

We create a function and pass it four arguments original string array, substring array, position and length of desired substring. As call by reference is used we do not need to return substring array. See another code below in which we return pointer to substring, which we create in our array using dynamic memory allocation.

#include <stdio.h>
 
void substring(char [], char[], int, int);
 
int main() 
{
   char string[1000], sub[1000];
   int position, length, c = 0;
 
   printf("Input a string\n");
   gets(string);
 
   printf("Enter the position and length of substring\n");
   scanf("%d%d", &position, &length);
 
   substring(string, sub, position, length);
 
   printf("Required substring is \"%s\"\n", sub);
 
   return 0;
}
 
void substring(char s[], char sub[], int p, int l) {
   int c = 0;
 
   while (c < l) {
      sub[c] = s[p+c-1];
      c++;
   }
   sub[c] = '\0';
}

C substring program using pointers

#include <stdio.h>
#include <stdlib.h>
 
char* substring(char*, int, int);
 
int main() 
{
   char string[100], *pointer;
   int position, length;
 
   printf("Input a string\n");
   gets(string);
 
   printf("Enter the position and length of substring\n");
   scanf("%d%d",&position, &length);
 
   pointer = substring( string, position, length);
 
   printf("Required substring is \"%s\"\n", pointer);
 
   free(pointer);
 
   return 0;
}
 
/*C substring function: It returns a pointer to the substring */
 
char *substring(char *string, int position, int length) 
{
   char *pointer;
   int c;
 
   pointer = malloc(length+1);
 
   if (pointer == NULL)
   {
      printf("Unable to allocate memory.\n");
      exit(1);
   }
 
   for (c = 0 ; c < length ; c++)
   {
      *(pointer+c) = *(string+position-1);      
      string++;   
   }
 
   *(pointer+c) = '\0';
 
   return pointer;
}

C code for all substrings of a string

#include <stdio.h>
#include <string.h>
#include <malloc.h>
 
char* substring(char*, int, int);
 
int main() 
{
   char string[100], *pointer;
   int position = 1, length = 1, temp, string_length;
 
   printf("Enter a string\n");
   gets(string);
 
   temp = string_length = strlen(string);
 
   printf("Substring of \"%s\" are\n", string);
 
   while (position <= string_length)
   {
      while (length <= temp)
      {
         pointer = substring(string, position, length);
         printf("%s\n", pointer);
         free(pointer);
         length++;
      }
      temp--;
      position++;
      length = 1;
   }
 
   return 0;
}
 
/* Use substring function given in above c program*/ 

Substring code output: