Edited code using ReadProcessMemory has issues - c++

Question

asked a question Call CloseHandle on handle that is a function parameter?
After someone edited the code, I updated it to find the code no longer works as intended.
intptr_t readMem(HANDLE processHandle, intptr_t address, int sizeToReadBytes)
{
intptr_t memValue = 0;
bool success = ReadProcessMemory(processHandle, (LPVOID)address, memValue, sizeToReadBytes, NULL);
if (!success)
std::wcout << "Memory read failed on address: " << std::hex << address << "\n";
return memValue;
}
In the line
ReadProcessMemory(processHandle, (LPVOID)address, memValue, sizeToReadBytes, NULL);
The memValue wouldn't compile without (LPVOID) or (LPCVOID) casts, but with them the code no longer reads the memory (or writes in the case of the functions using WriteProcessMemory
Originally (and now I've changed it back in my little program) it uses a reference &memValue and works fine.
My question is:
Should this work?
Or is the edit correct and the rest of my program potentially wrong?
I can provide more code if needed, just not sure which bits and didn't want to clog up the screen more than I have... Also should I rollback the edit?

Answer 1

The third parameter of ReadProcessMemory() is a memory address in the calling process where the function writes the read data to. You are not passing a memory address, though. In the code shown in the third revision to the original question, you were type-casting the value of an uninitialized integer variable into a memory pointer. So the function would try to write to random memory. Now you have removed the type-cast, so the code should not even compile anymore.
Your readMem() function is not designed correctly. You need to change it so that either:
The caller allocates memory of the required size and then the function simply fills the memory:
bool readMem(HANDLE processHandle, intptr_t address, void *memValue, int sizeToReadBytes)
{
bool success = ReadProcessMemory(processHandle, (LPVOID)address, memValue, sizeToReadBytes, NULL);
if (!success)
std::wcout << "Memory read failed on address: " << std::hex << address << "\n";
return success;
}
intptr_t memValue = 0;
readMem(processHandle, address, &memValue, sizeof(memValue));
The function allocates memory and returns it to the caller:
void* readMem(HANDLE processHandle, intptr_t address, int sizeToReadBytes)
{
uint8_t memValue = new uint8_t[sizeToReadBytes];
bool success = ReadProcessMemory(processHandle, (LPVOID)address, memValue, sizeToReadBytes, NULL);
if (!success) {
std::wcout << "Memory read failed on address: " << std::hex << address << "\n";
delete [] memValue;
memValue = NULL;
}
return memValue;
}
intptr_t *memValue = (intptr_t*) readMem(processHandle, address, sizeof(intptr_t));
...
delete [] memValue;
Or:
bool readMem(HANDLE processHandle, intptr_t address, int sizeToReadBytes, std:vector<uint8_t> &memValue)
{
memValue.resize(sizeToReadBytes);
bool success = ReadProcessMemory(processHandle, (LPVOID)address, &memValue[0], sizeToReadBytes, NULL);
if (!success)
std::wcout << "Memory read failed on address: " << std::hex << address << "\n";
return success;
}
std::vector<uint8_t> buffer;
readMem(processHandle, address, sizeof(intptr_t), buffer);
intptr_t memValue = (intptr_t*) &buffer[0];