Pointers to pointers

[CeeCee]

What are they really good for? In every case of pointers that I've seen, just one pointer would work fine yet the programmer chose a pointer to a pointer. Why would I want to use that instead of just one pointer when one would work fine?

[AndersSundman]

Sometimes you wan't to pass a pointer to a function as a reference (so that the pointer value can be changed).

Say that the pointer points to the pixels in an image and you have a function for loading an image from disk imgLoad(), this function might take as an argument a pointer to a pointer..

imgLoad(void** pixels);

This way you can allocate memory inside the function, and make the void* pixels pointer point to the new memory.. caling the function with:

PIXELS* myPixels;
imgLoad(&myPixels);

This can be usefull sometimes..

Besides that double arrays are a good example, as pointed out by the vVv. Note that you don't have to make all row's in a double array equaly long.. You can have one loking like:

******
***
*****
**

This is hard to do with [row*width + col] in a single array beeing used as a double..

- Anders

- Anders