return pointer to data declared in function

Question

I know this won\'T work because the variable x gets destroyed when the function returns:

int* myFunction()
{
    int x = 4; return &x;
}

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Answer 1

C++ approach to avoid memory leaks. (at least when You ignore function output)

std::auto_ptr myFunction() {
    std::auto_ptr result(new int(4));
    return result;
}

Then call it:

std::auto_ptr myFunctionResult = myFunction();

EDIT: As pointed out by Joel. std::auto_ptr has it's own drawbacks and generally should be avoided. Instead std::auto_ptr You could use boost::shared_ptr (std::tr1::shared_ptr).

boost::shared_ptr myFunction() {
    boost::shared_ptr result(new int(5));
    return result;
}

or when use C++0x conforming compiler You can use std::unique_ptr.

std::tr1::unique_ptr myFunction() {
    std::tr1::unique_ptr result(new int(5));
    return result;
}

The main difference is that:

• shared_ptr allows multiple instances of shared_ptr pointing to the same RAW pointer. It uses reference counting mechanism to ensure that memory will not be freed as long as at least one instance of shared_ptr exist.

• unique_ptr allows only one instance of it holding pointer but have true move semantic unlike auto_ptr.