Free function in c

Question

I have allocated memory to some data type and assigned some value. Now using free is the data in the memory deleted or not? What is use of using free if the data assigned is not deleted? Can anyone help me out? Ex:

int *arr;
arr=(int*)malloc(sizeof(int)*1000);
assert(arr!=NULL);
/*Some operation*/

arr[123]=354;
//some operations

printf("%d",*(arr+123));
//calling some funcs

free(arr);

printf("
%d",*(arr+123));

Answer 1

The point of free is to make the memory you allocated available for following calls to malloc. It does not guarantee that the buffer passed to it is wiped in any way.

In fact, what you're doing is provoking undefined behavior; accessing a buffer that has been free'd might give the value that was previously stored in it, or any other value, or it might crash your program, or do anything else.