Control reaches end of non-void function: why only a warning?

[Pierre Sarrazin <sarrazip@xxxxxxxxxxxx>]

The following code generates the warning "control reaches end of
non-void function" under g++ 3.4.2:

int g()
{
}

Why is this only a warning and not an error?

-- 
Pierre Sarrazin <sarrazip at sympatico dot ca>