Question

In C++, why is the following element access in a vector invalid?

void foo(std::vector<int>* vecPtr) {
  int n = vecPtr->size(); // ok
  int a = vecPtr->[0];    // invalid
}

Instead, we have to write the more cumbersome

  (*vecPtr)[0] = 1;

I think, the operator[] call should just have the same syntax like a method call, and I hate the extra star and parentheses. (I know C++ has a lot more serious issues, but this one annoys me every time when I have to type it …)

Answer 1

It’s because the language expects a member to appear after ->. That’s how the language is made up. You can use the function call syntax, if you like

// not really nicer
vecPtr->operator[](0);

If you have to do this a lot in sequence, using [0] instead of the parentheses can improve readability greatly

vecPtr[0][0]

Otherwise, for one level, i find (*vecPtr)[0] is perfectly readable to me.