How do I properly convert a pointer (uint8_t* or void*) to a “normal” integer?

Question

I'm writing a program for arduino that needs dynamic memory allocation frequently, but as I don't want the memory to get fragmented, I'm also writing a "memory handler" for it. This memory handler would need to do calculations involving both pointers and size_t variables, like this (example code is not part of program, but the structure of the calculations is the same):

size_t freeMemSize = nextPointer - currentPointer - currentSize;

Which would calculate the size of free memory between two reserved spaces.

Of course, arduino doesn't want to swallow this code, as it compares incompatible types. My questions are:

• Is a cast to the correct integer type enough to solve the problem?
• If it is, what is the "normal integer" counterpart of a pointer?

I guess this varies from processor to processor, so I should look for something like size_t, but for memory indices instead of sizes.

Board: Uno, Nano
IDE version: 1.8.2

Answer 1

Assume the following declarations:

uint8_t* nextPointer;
uint8_t* currentPointer;
size_t currentSize;

Then the expression is valid:

size_t freeMemSize = nextPointer - currentPointer - currentSize;

If any of the pointers are void* the compiler cannot calculate the expression (pointer or size).

Cheers!