c++ - Why does returning a reference to a automatic variable work? -

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i'm reading c++, , read when using return reference should make sure i'm not returning reference variable go out of scope when function returns.

so why in add function object cen returned reference , code works correctly?!

here code:

#include <iostream> using namespace std;  class cents {  private:  int m_ncents;   public:  cents(int ncents) { m_ncents = ncents; }  int getcents() { return m_ncents; } };  cents& add(cents &c1, cents &c2) {    cents cen(c1.getcents() + c2.getcents());    return cen; }  int main() {    cents ccents1(3);    cents ccents2(9);    cout << "i have " << add(ccents1, ccents2).getcents() << " cents." << std::endl;     return 0; }

i using codeblocks ide on win7.

this undefined behavior, may seem work can break @ anytime , can not rely on results of program.

when function exits, memory used hold automatic variables released , not valid refer memory.

the draft c++ standard in section 3.7.3 paragraph 1 says:

block-scope variables explicitly declared register or not explicitly declared static or extern have automatic storage duration. the storage these entities lasts until block in created exits.


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