VirtualAlloc MEM_COMMIT and MEM_RESERVE

Question

I'm a little confused with VirtualAlloc,

We can reserve the memory usage of MEM_RESERVE and then commit it with MEM_COMMIT, but I'm a little confused about what the difference is when using between the two functions below:

m_pvData = VirtualAlloc(NULL, m_nBuffSize, MEM_COMMIT, PAGE_READWRITE);
m_pvData = VirtualAlloc(NULL, m_nBuffSize, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);

What is the benefit of choosing the second option?

And I can use the function below to get the buffer:

void* pdata = VirtualAlloc(NULL, 64*1024*1024, MEM_COMMIT, PAGE_READWRITE);
if (pdata == NULL)
{
    cout<<"Last error is "<<GetLastError()<<endl;
}

Error

Answer 1

The difference is this: with MEM_RESERVEyou basically say to the operating system: "Hey, please, I need this continuous block of pages of virtual memory, can you give me a memory address that suits my needs?"

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