当我使用new运算符分配大小为1k字节的内存时，操作系统在Windows中会做什么？

Question

It seems that memory leak occurs in my code, so I try to locate the place in my code which causes the memory leak.

In the post Can't obtain accurate information of available memory in the heap I was told that OS may allocate large memory when a small memory is request to reduce the system call.

Is it correct in Windows?

Answer 1

What's relevant here, after seeing your other question, is not what happens when you allocate memory. What matters is what happens when you release it. In particular a 1 KB allocation will never be released back to the OS, it is too small. It gets added to a list of free blocks, ready to be used by the next allocation of (about) the same size.

You cannot reliably detect memory leaks with VirtualQuery().

If you use Visual Studio then use its built-in leak detection feature . There are plenty of other tools.

Answer 2

On most systems (including most recent compilers on Windows), the heap manager will allocate relatively large "chunks" of memory from the OS, then divide that up into pieces for use by the program. That allocation from the OS will typically be at least tens of kilobytes.

Those large chunks of memory will be returned to the OS when the program ends execution. It can happen sooner than that, but end of execution is the most common.

Each of those large chunks will be tracked by the OS as a single allocation (even though the heap manager will then break it up into smaller pieces for use by your code). Any that have been released back to the OS will show up as free memory blocks.