C++ empty program memory leak

Question

Consider the following code

int main(){
    return 0;
}

I compiled it with g++ and passed the output to valgrind. The output is the following.

==11752== HEAP SUMMARY:
==11752==     in use at exit: 72,704 bytes in 1 blocks
==11752==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==11752== 
==11965== LEAK SUMMARY:
==11965==    definitely lost: 0 bytes in 0 blocks
==11965==    indirectly lost: 0 bytes in 0 blocks
==11965==      possibly lost: 0 bytes in 0 blocks
==11965==    still reachable: 72,704 bytes in 1 blocks
==11965==         suppressed: 0 bytes in 0 blocks

However, compiling the same code in C with gcc produces this valgrind output:

==11771== HEAP SUMMARY:
==11771==     in use at exit: 0 bytes in 0 blocks
==11771==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==11771== 
==11771== All heap blocks were freed -- no leaks are possible

It looks like compiling

It looks like the empty C++ program actually allocates memory and does not free it (it's not a disaster since it's a "still reachable" leak), and I have no clue why this is happening.

I did this test on linux (solus os) with g++ 6.3.

Can someone explain what's going on ?

Couldn't reproduce on gcc 4.7.1. It's probably a bug in 6.3 version, consider reporting it. — mcrlc, Mar 18 '17 at 20:23
Possible duplicate of [Valgrind: Memory still reachable with trivial program using ](http://stackoverflow.com/questions/30376601/valgrind-memory-still-reachable-with-trivial-program-using-iostream) — cbuchart, Mar 18 '17 at 23:54

score 1 · Answer 1 · edited Jan 12 '21 at 17:55

it's not a disaster since it's a "still reachable" leak

It's not even a leak. It is extremely common for programs to not free a block of memory that some global points to; doing the freeing is

unnecessary work that just makes the program exit slower
may cause complications if multiple threads are running (exiting thread may yank carpet from under the other thread)
may cause complications if other parts of cleanup can access this block, etc. etc.

I have no clue why this is happening.

To get a clue, run valgrind --leak-check=full --show-reachable=yes .... That will tell you where the block was allocated.

C++ empty program memory leak

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