Quoting al davis <[EMAIL PROTECTED]>:
On Friday 12 May 2006 18:24, Ilia Mirkin wrote:
Also, when you do
vector<int> x;
x[0] = 5;
keep in mind that internally it instantiates a new int
object, and then calls operator= on it. The compiler might
optimize this to a certain extent, but certainly not to the
level of simplicity of a single memory access/write.
A good compiler will optimize it that well.
Your code is wrong. The vector x is of size zero. It should
crash.
You need:
vector<int> x;
x.reserve(5);
x[0] = 5;
or:
vector<int> x(5);
x[0] = 5;
OK, I suppose I was just giving an *idea* of what I was comparing rather than
fully working compiled code. But you're right -- I just checked the generated
code, and the only difference came from the array being on the stack vs
somewhere on the heap, which is to be expected. I hadn't realized that
compilers had come this far in terms of STL optimization.
-Ilia
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