Is _ (single underscore) a valid C++ variable name?

Question

With gcc 4.7.2 this compiles just fine for me:

int main()
{
  int _ = 1;
  return 0;
}

Can I expect this to compile in general? I\'ve read

Answer 1

But why having this weird name '_' for a variable? Does it mean you do not want no one access it again or something? Saw code looks like:

for (auto _ : ) {
    // some code that does not have '-' at all
}