Question

I need help with my C code. I have a function that sets a value to the spot in memory
to the value that you have input to the function.

The issue that I am facing is if the pointer moves past the allocated amount of memory
It should throw an error. I am not sure how to check for this issue.

 unsignded char the_pool = malloc(1000);
 char *num = a pointer to the start of the_pool up to ten spots
 num[i] =  val;
num[11] = val; //This should throw an error in my function which 

So how can I check to see that I have moved into unauthorized memory space.

Answer 1

C will not catch this error for you. You must do it yourself.

For example, you could safely wrap access to your array in a function:

typedef struct
{
   char *data; 
   int length;
} myArrayType;

void MakeArray( myArrayType *p, int length )
{
   p->data = (char *)malloc(length);
   p->length = length;
}

int WriteToArrayWithBoundsChecking( myArrayType *p, int index, char value ) 
{
   if ( index >= 0 && index < p->length ) 
   { 
      p->data[index] = value;
      return 1; // return "success"
   }
   else 
   {
      return 0; // return "failure"
   }
}

Then you can look at the return value of WriteToArrayWithBoundsChecking() to see if your write succeeded or not.

Of course you must remember to clean up the memory pointed at by myArrayType->data when you are done. Otherwise you will cause a leak.