C++ pointers and arrays - c++

Question

I have a problem with dynamic array.
In header file class i have this:
class CTerrain
{
...
CRock *rocks;
int numRocks;//=0
...
}
and in cpp i have this:
void CTerrain::Create()
{
numRocks = 0;
int NUM_ROCKS = rand()%10+1;
for(int i=0;i<NUM_ROCKS;i++)
{
rocks = new CRock;
numRocks++;
...
}
}
void CTerrain::Render()
{
for(int i=0;i<numRocks;i++)
rocks[i].render();//it works ok when here is 0 instead of 'i'
}
When I run this code I got error:
Unhandled exception at 0x00913aea in OpenGL.exe: 0xC0000005: Access violation reading location 0x1c00001f.
Thanks for any help, I have been trying to resolve this problem for like 4 hours...
EDIT:
Ok, so I changed Create() method to this:
void CTerrain::Create()
{
numRocks = 0;
int NUM_ROCKS = rand()%10+1;
rocks = new CRock[NUM_ROCKS];
for(int i=0;i<NUM_ROCKS;i++)
{
rocks[i].position = ...
numRocks++;
...
}
and also added delete [] rocks and now it's working.

Answer 1

Your Create function would be more like
void CTerrain::Create()
{
int NUM_ROCKS = rand()%10+1;
rocks = new CRock[NUM_ROCKS];
numRocks = NUM_ROCKS;
for(int i=0; i<NUM_ROCKS; i++)
{
rocks[i] = CRock{};
}
}

Answer 2

Just to add bit of explanation to above answer. Here:
for(int i=0;i<NUM_ROCKS;i++)
{
rocks = new CRock;
numRocks++;
...
}
What you do is, each time assign new instance of CRock to the pointer rock; thereby losing reference to the old object and creating memory leaks. Use a solution similar suggester by Cyber.

Answer 3

First off, rocks is pointer to CRocks. Your implemenation:
rocks[i].render() should be something like this:
rocks = new CRock [x]; (where x is the number of objects of type CRock.)
rocks[i] -> render().
delete rocks[i] // Just be sure to delete.
You may want to reference this for your solution on handling how a dynamic array of objects.
This other reference is good.

Answer 4

rocks = new CRock;
you overwrite CRock* pointer rocks in this line over and over again
Use this
rocks = new CRock[NUM_ROCKS];