Question

Working on a program where my task is to implement a library (as a set of source and header files, documentation, and a Makefile) that provides a few useful functions for working with a counted string data structure.

And one of the functions that needs to be written is described below but I am having a little difficulty writing it. Program needs to be written in C.

void kstrcat(kstring *destp, kstring src)

Concatenates str onto the end of *destp. First extends *destp to be long enough to hold the contents of both strings, by calling kstrextend(). Then copies the contents of src into the dest

So, for example, if we execute the following code:

      kstring a = kstrfrom("hello"); // 6 bytes including \0
      kstring b = kstrfrom("world"); // 6 bytes including \0
      kstrcat(&a, b);

Now a should have length 12, and the contents "hello\0world\0".

Note that this function takes a pointer to the destination kstring. That means that changes you make to the destp->length and destp->data members will be visible to the caller.

Note: Remember to save the original length of *destp before calling kstrextend(). Otherwise, you won't know where to copy src's data to!

#include<stdio.h>
typedef struct
{
char *data;
size_t length;
} kstring;

void kstrextend(kstring *strp, size_t nbytes){
if(strp->length>=nbytes)
return;
char *p;
p=(char*)malloc(nbytes*sizeof(char));
if(p==NULL)abort();
int i=0;//iterates till it reaches null character of current array
while(strp->data[i]!='\0')
{

//copies current character of original array
p[i]=strp->data[i];
i++;
}
//already copied the stuff
//now we fill up the remaining section
while(i<nbytes){
//appending null strings to remaining character
p[i]='\0';
i++;
}
//frees the previous array
free(strp->data);
//changes pointer to new attributes
strp->data=p;
strp->length=nbytes;
}

Answer 1

C code:

#include<stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct
{
char *data;
size_t length;
} kstring;

kstring kstralloc(size_t nbytes){

int i;
  
kstring new_kstring; // creating a object of type ksting
  
new_kstring.data =(char*) malloc(nbytes); // allocating nbytes of memory to create string of length nbytes
  
if (new_kstring.data == NULL && nbytes!= 0){
printf("There is an error allocating memory ");
abort();
}
  
new_kstring.length = (int)nbytes; // setting length member to size mentioned using nbytes
  
// initializinf by filling it with nbytes copies of the null byte ('').
for (i= 0;i<nbytes;i++)
new_kstring.data[i] = '';   
  
return new_kstring;
}

void kstrextend(kstring *strp, size_t nbytes){
if(strp->length>=nbytes)
return;
char *p;
p=(char*)malloc(nbytes*sizeof(char));
if(p==NULL)abort();
int i=0;//iterates till it reaches null character of current array
while(strp->data[i]!='')
{

//copies current character of original array
p[i]=strp->data[i];
i++;
}
//already copied the stuff
//now we fill up the remaining section
while(i<nbytes){
//appending null strings to remaining character
p[i]='';
i++;
}
//frees the previous array
free(strp->data);
//changes pointer to new attributes
strp->data=p;
strp->length=nbytes;
}

void kstrcat(kstring *destp, kstring src)
{
   size_t l=destp->length;
   kstrextend(destp,destp->length+src.length);
   destp->length=l+src.length;
   int i;
   for(i=l;i<l+src.length;i++)
   {
       destp->data[i]=src.data[i-l];
   }
   destp->data[i]='';
  
}

int main()
{
size_t i = 5;
  
kstring kstr1 = kstralloc(i); // Allocating memory for data member

strcpy(kstr1.data, "Hello");
printf("Data : %s Lenght : %d",kstr1.data,kstr1.length);

   kstring kstr2 = kstralloc(5); // Allocating memory for data member
strcpy(kstr2.data, "World");
printf(" Data : %s Lenght : %d",kstr2.data,kstr2.length);

kstrcat(&kstr1,kstr2);
printf(" Data : %s Lenght : %d",kstr1.data,kstr1.length);
}

output: