是否可以在不使用malloc的情况下进行内存泄漏？

Question

This question is as in title: Is it possible to produce a memory leak without using any kernel specific means like malloc, new, etc?

What if I will make a linked list inside a function with lot of elements in there, and after it I'll exit from this function without cleaning a list. The list will be created without using any malloc calls, ie

struct list_head {
     struct list_head *next, *prev;
}

Can it be guaranteed that all resources will be freed after exiting from this function? So I can freely execute it a million times and nothing will be leaked?

Subject: If you not using any particular malloc or new calls you won't get a heap memory leak. Never. Is that right?

Answer 1

A leak is always connected to a resource . A resource is by definition something that you acquire manually, and that you must release manually. Memory is a prime example, but there are other resources, too (file handles, mutex locks, network connections, etc.).

A leak occurs when you acquire a resource, but subsequently lose the handle to the resource so that nobody can release it. A lesser version of a leak is a "still-reachable" kind of situation where you don't release the resource, but you still have the handle and could release it. That's mostly down to laziness, but a leak by contrast is always a programming error.

Since your code never acquires any resources, it also cannot have any leaks.

Answer 2

The variables you applied without malloc or new is located at stack space in the memory. So when the function returned, the variable is taken back.

On the other hand, the memory you applied with malloc or new is located at heap space. The system doesn't care whether you release the space or not. In this situation, if you don't use free or delete, memory leak will happen.

Answer 3

Subject: If you not using any particular malloc or new calls you won't get a heap memory leak. Never. Is that right?

That assumption is not entirely correct. The problem is that the operating system itself (or other third party components you have to rely on) can have memory leaks as well. In that case you might not actively call malloc, but call other (operating system) functions which could leak.

So your assumption depends on how strongly you consider such a thing. You can argue that the OS/third party implementation is outside your domain, then this assumption would be correct. If you have a well defined system and your requirements are such that you have to garuantee a certain uptime, something like this may have to be considered as well.

So the answer to this question ...

Is it possible to make memory leak without using malloc?

... is:

Yes, it is possible.

Answer 4

malloc() allocates memory from the heap, while space for string and struct literals ( string1 , string2 and those list_head 's) will be reserved at compile time at the stack.

Actually any memory allocated for a program (heap or stack) will be reclaimed by the kernel when the process exits (at *nix system at least).

I would define memory leak as allocating memory on heap and without freeing it when your program exits. This definition actually answers your question.

There are standard functions (like strdup ) that will allocate memory on heap, beware of them.

Answer 5

Another example of a resource that you can allocate and forget to free:

If you're using OpenGL, and you call glGenBuffers() a million times without the corresponding glDeleteBuffers calls, it's extremely likely that you will run out of VRAM and your graphics driver will start leaking to system memory.

I just had this happen. Fortunately, Visual Studio's memory profiler made it pretty easy to find. It showed up as a large number of allocations made by the external process nvoglv32.dll , which is my NVIDIA OpenGL driver.