ulrik@kaizer.se/ log/
tech

Here is some fun with C++11's constexpr. It seems we can check substring containment at compile time. The following example works fine with GCC 4.6.1.

#include <iostream>
#include <array>

constexpr bool not_end(const char *s, const int n) {
        return s && s[n];
}

/* does `s` have `t` as prefix. Use offsets ns, nt */
constexpr bool str_prefix(const char *s, const char *t, const int ns, const int nt) {
        return (s == t) || !*(t + nt) || (*(s + ns) == *(t + nt) && (str_prefix(s, t, ns+1, nt+1)));
}

constexpr int contains1(const char *s, const char *needle, const int n) {
        return not_end(s,n) && (str_prefix(s, needle, n, 0) || contains1(s, needle,n+1));
}

constexpr int contains(const char *s, const char *needle) {
        return contains1(s, needle, 0);
}

const int x = contains("froogler", "oogle");

int main(void) {
        std::array<int, 10 * contains("hi there", "the")> a;
        std::array<int, 10 * contains("hi thre", "the")> b;
        std::cout << "Array size for a is " << a.size() << "\n";
        std::cout << "Array size for b is " << b.size() << "\n";
        std::cout << "x: " << x << "\n";
}

It compiles without warnings using the commandline:

g++ -Wall -std=c++0x -o constarray constarray.cc

And produces the following output:

Array size for a is 10
Array size for b is 0
x: 1

So, is this a legal part of C++11? Is it a good thing? It is at least a more readable compile-time language than template metaprogramming.

If you want to contact me, I'm @englabenny on twitter

Edit to add a Bonus: an implementation of foldr over initializer lists, see C++ constexpr foldr

A big thank you to all that participated in the 1st of April beta testing stint of Kupfer's version v205. It has been decided that we can deliver a superior experience to our users if we discontinue the ASCII icon set in future releases. The ASCII icon set will however remain as an plugin.

Stay tuned for kupfer v206 this coming week which will include the final bug fixes and translations. Don't hesitate take part in bugreporting.

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Finally, kupfer is released with the latest version v205. This is a really nice release, a bit of a prerelease actually; we simply can't let the new stuff wait in a stable branch until it gets cold.

We are adding all the things we promised when posting the latest version (Welcome to Kupfer v204), and more than that as well. Please report any bugs that you find.

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Finally, kupfer is released with the latest version v204. Many small or large bugs and problems have been fixed and we are also introducing some useful new stuff.

First and foremost, I hope that the expanded Kupfer User Manual will be a great help to new and old users. It includes a keyboard shortcuts reference, lots of tips and basic usage help for the most important plug-ins. Kupfer has been lacking in documentation and hopefully it will grow larger with time. Also thanks to the awesome translators of the documentation, and of Kupfer as a whole!

Feedback & comments to @englabenny on twitter or @kaizer on identi.ca, or use hashtag #kupfer. The Kupfer project itself also has a mailing list