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Question about constants

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What does it mean: const int function() { // something.. } i understand that it means that you cannot change the return value, but how can i change the return value..?

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In this particular situation, it is completely useless, since the returned value would be a temporary value (and thus, wouldn't be modifiable) anyway.

However, you may wish to return a value by reference (perhaps to avoid creating a copy of the value, or perhaps because you want changes applied to that value to be received by the holder of the return value) but do not wish to let the one who called the function modify the referenced value.

A typical example is v.front() when v is a const std::vector<int> (at which point, the function returns a const int &).

void foo(const std::vector<int> & v)
// Function foo may not alter the vector which
// it receives, and this includes altering the
// value of its first element!
const int & i = v.front();
std::cout << i << "\n";

// However, it's possible to alter the vector
// through a variable other than 'v', perhaps
// if the original vector is a global variable
// that was passed as an argument:
g_v[0] = 100;

// And now, this outputs 100.
std::cout << i << "\n";

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