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.

Struct:

typedef struct
{
   char *data;
   size_t length;
} kstring;

function:

void kstrextend(kstring *strp, size_t nbytes)

Modifies an existing kstring, pointed to by strp, to be at least nbytes bytes long.

If strp->length was already nbytes or longer, does nothing. That is, this function will never reduce the length of a string, only increase it.

If nbytes is longer than the current length, this function should take the following steps:

1. Allocate a new array with the larger size.
2. Copy data over from the old array to the new one.
3. Free the old array.
4. Fill the additional elements of the new array with null bytes ('\0').
5. Make strp->data point to the new array.
6. Set strp->length to the new size.

Note: if you are using malloc() for memory allocation, the function realloc() (Links to an external site.)Links to an external site. will take care of steps 1, 2, and 3 with a single function call.

If there is an error allocating memory, this function should call abort().

Note that this function takes a pointer to a kstring rather than taking a kstring by value. That means that changes you make to the strp->length and strp->data members will be visible to the caller.

Answer 1

I used malloc, so that you have a better understanding of how the process works.

Malloc has a void return type, so you need to typecast it to the required datatype after memory is allocated.

Neverthless, if it fails to allocate memory, it will return NULL. If so, we call abort().

//REST OF THE EXPLANATION IN COMMENTS

#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;
}
void main()
{
kstring name;
name.data="Chegg";
name.length=5;
kstrextend(&name,40);
printf("%s %d",name.data,name.length);
}