Howard Hinnant wrote:
On May 27, 2005, at 1:47 PM, Peter Dimov wrote:
Howard Hinnant wrote:
2. Uninitialized is better because it is much faster, especially if you have containers of such elements. You can always explicitly initialize if you want.
Technically... you can't put an uninitialized (non-character) scalar in a container; copying an uninitialized scalar is undefined behavior.
<gets an evil look in his eye...>
#include <array> #include <vector> #include <tupleio> #include <iterator> #include <algorithm> #include <iostream>
int main() { std::vector<std::tr1::array<int, 3> > v; std::tr1::array<int, 3> a; for (int i = 0; i < 10; ++i) v.push_back(a); std::ostream_iterator<std::tr1::array<int, 3> > out(std::cout, "\n"); copy(v.begin(), v.end(), out); }
(1 0 3195936) (1 0 3195936) (1 0 3195936) (1 0 3195936) (1 0 3195936) (1 0 3195936) (1 0 3195936) (1 0 3195936) (1 0 3195936) (1 0 3195936)
Ha, ha, did it! And you can't stop me from doing it again! <evil laugh follows> :-)
But what for? If you want to print random values to stdout, it's easier to just use std::rand. Didn't we already go over this some years ago? The result was a proposed vector constructor that left its members uninitialized and then called a user-supplied function that initialized them. And in any event, compressed_pair leaving its members uninitialized when std::pair doesn't is a pretty elegant way to sneak bugs into innocent people's code when they aren't looking. An <evil laugh> would be entirely appropriate here as well. ;-)