scope of pointers to (local) objects declared within a for loop

Question

Dear all,

I'm not sure if the snippet of C++ code below is legitimate or not:

std::vector<int*> myints;
for (int i = 0; i<N; i++) {
   int j = i;
   myints.push_back(&j);
 }

 for (int i=0; i<myints.size(); i++) cout<<*(myints[i])<<endl;

How does the compiler handle this ? I understand the variable j itself goes out of scope when exiting the for loop but will an integer be locally allocated N times on the stack so that the int objects pointed to by the elements in the vector remain valid outside the loop ?

Many Thanks ! -bert

Answer 1

Once the block ends, the compiler stops caring about the memory that was previously reserved for them. But even if nothing else disrupts that, you have another problem: all the int*s in the vector<int*> point to the same memory location, so they all have the final value of i.

Answer 2

The answer depends (as usual) on compiler's implementation.

You will probably get all pointers pointing to the same location with N's latest value on its pointed direction.