CODEWITHSUNDEEP
c
rajya vardhan
rajya vardhan

Reputation: 1131

vector replication in c

how can i define an array in c which works like vector? This array should take any amount of values. It can take 0 values or 10 values or 100 values.

The code below works but gives me a runtime error that stack was corrupted.

int i = 0;
    int* aPtr = &i;
    int* head = aPtr;
    for(i=0;i<6;i++){
        (*aPtr)=i;
        aPtr++;
    }

Similarly how can i use char* str to take any amount of characters followed by null character in end to make a string?

Practice for interviews :)

Upvotes: 1

Views: 303

Answers (3)

gcbenison
gcbenison

Reputation: 11963

There are many ways to do this in C, depending on your requirements, but you said "any number of values" (which usually means as many as will fit in memory). That's commonly done using realloc to grow the size of an array dynamically. You'll need to keep some bookkeeping information too on the size of the array as it grows.

void
store (vector_t * v, int idx, int value)
{
  if (v->size < idx) {
     v->size = idx * 2;
     v->data = realloc(v->data, v->size);
  }
  v->data[idx] = value;
}

This being tagged "homework", I've left some details to fill in such as the definition of vector_t.

Upvotes: 2

flukey
flukey

Reputation: 187

This isn't too difficult. The important thing to remember is that you will need to initially allocate memory for your array using malloc(...) or calloc(...). After that you can easily allocate (or deallocate) memory as items are added or removed. The method for dynamically adding or removing memory (which is used to store the items in the array) is realloc(...). The wiki page for C Dynamic Memory Allocation is actually pretty informative. I've provided an example below showing how to initially allocate a char* array, then increase the size and decrease the size.

#include "stdio.h"
#include "stdlib.h"

int main()
{
  char *myDynamicString;

  /* allocate initial memory */
  myDynamicString = (char *)malloc(sizeof(char) * 2);
  myDynamicString[1] = '\0';

  /* set values */
  myDynamicString[0] = 'A';

  /* prints: A */
  printf("String: %s\n", myDynamicString);

  /* make string bigger */
  myDynamicString = (char *)realloc(myDynamicString, sizeof(char) * 6);
  myDynamicString[5] = '\0';

  /* set values */
  myDynamicString[1] = 'P';
  myDynamicString[2] = 'P';
  myDynamicString[3] = 'L';
  myDynamicString[4] = 'E';

  /* prints: APPLE */
  printf("Bigger String: %s\n", myDynamicString);

  /* make string smaller */
  myDynamicString = (char *)realloc(myDynamicString, sizeof(char) * 3);
  myDynamicString[2] = '\0';

  /* set values */
  myDynamicString[1] = 'Z';

  /* prints: AZ */
  printf("Smaller String: %s\n", myDynamicString);

  /* don't forget to release the memory */
  free(myDynamicString);

  return 0;
}

Upvotes: 1

woodstok
woodstok

Reputation: 2794

In Your for loop , after the first iteration, you are trying to access aPtr which points to a memory location which was not declared or reserved before. In the first iteration, the int i did the memory allocation for you.

What you could do though would be to initally allocate the memory required using malloc . Once this memory is allocated , and if you walk through only the allocated stack space, you wont come across a run time error.

PS:Your code does not work if it just compiles. Any program may contain run time as well as compile time errors. Your code sample is a very common example of run-time error.

Upvotes: 1

Related Questions