当 reset(） 被unique_ptr调用两次时会发生什么?

我有以下程序，我在其中调用mc.reset((两次。我以为这会给我一个错误，但这没有错误。

#include <iostream> 
#include <csignal> 
#include <memory>  // for unique pointer
using namespace std; 
std::unique_ptr<int> mc;
void signal_handler( int signal_num ) { 
cout << "The interrupt signal is (" << signal_num << "). n"; 
mc.reset();
mc.reset();
// terminate program   
exit(signal_num);   
} 
int main () {
mc.reset (new int); 
*mc = 5;
// Press Control + c to raise SIGINT
signal (SIGINT, signal_handler);
while(true) 
cout << "Hello..." << endl; 
return 0;
}

我使用 valgrind 检查内存泄漏，但没有发现：

==5467== 
==5467== HEAP SUMMARY:
==5467==     in use at exit: 0 bytes in 0 blocks
==5467==   total heap usage: 3 allocs, 3 frees, 73,732 bytes allocated
==5467== 
==5467== All heap blocks were freed -- no leaks are possible
==5467== 
==5467== For counts of detected and suppressed errors, rerun with: -v
==5467== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

调用重置时实际发生了什么？为什么我可以毫无问题地调用它两次？