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gooooloo/memleak.cpp

Last active Jul 24, 2019
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What would you like to do?
a memory leak example in practice
/**
* Here is an example of mem leak I met today. I didn't write the codes, I just help finding the memleak.
* Of course the real code is much more complicated, I simplify it here.
*
* To prove there is memleak, just compile and run:
* $ gcc a.cpp --std=c++11 -lstdc++ && ./a.out
*
* And you will see below:
* 4 bytes leaked.
*
* The interesting thing is why only 4 bytes is leaked.
**/
#include <vector>
#include <queue>
#include <functional>
#include <iostream>
int size = 0;
struct A {
int *p = 0;
~A() { if (p) { delete p; size -= 4;} }
A &operator =(A &other) {
if (p) { delete p; size -= 4; }
p = other.p;
other.p = 0;
return *this;
}
void foo() { p = new int(3); size += 4;}
};
void bar(A *pa) {
A a;
a.foo();
*pa = a;
}
int main(int, char **) {
{
std::queue<std::function<void (void)>> jobs;
const int N = 200;
// mem leak version
std::vector<A> v;
for (int i = 0; i < N; i++) {
A a;
jobs.emplace(std::bind(bar, &a));
v.push_back(a);
}
// // ok version
// std::vector<A> v(N);
// for (int i = 0; i < N; i++) {
// jobs.emplace(std::bind(bar, &v[i]));
// }
while (!jobs.empty()){
auto job = std::move(jobs.front());
jobs.pop();
job();
}
}
std::cout << size << " bytes leaked." << std::endl;
return 0;
}
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