Блог пользователя angelbeats

Автор angelbeats, история, 4 года назад, По-английски
namespace std {
void debug_out() { cerr << endl; }
template<typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << to_string(H);
    debug_out(T...);
}
#ifdef LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: ", debug_out(__VA_ARGS__)
#define tee(...) [](const auto& x){ cerr << "[" << #__VA_ARGS__ << "]: "; debug_out(x); return x; }(__VA_ARGS__)
#else
#define dbg(...) do {} while(0)
#define tee(...) (__VA_ARGS__)
#endif
}

The code above introduces tee, which simply prints one value and returns it.

g++ -DLOCAL -O2 --std=c++17 -o a a.cpp

Don't use c++11. Don't change std to other names. You can get rid of the std wrapper.

And here's the complete version, which handles tuple of any length, as well as complex.

Complete version

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Автор angelbeats, 4 года назад, По-английски
portable version
#include <tuple>
using namespace std;
#define numargs(args...) tuple_size<decltype(make_tuple(args))>::value
#define argi(i, args...) get<i>(make_tuple(args))
#define rep(i, args...) for (int i = ((numargs(args) > 1) ? argi(0, args) : 0); i < argi(numargs(args) - 1, args); ++i)
#define repi(args...) rep(i, args)

First, let argv := make_tuple(args), to get argc out of args, we use argc := tuple_size<decltype(argv)>::value, according to link. Second, we use (argc - 1 > 0) ? get<1>(argv) : 0 as the base, and get<(argc - 1)>(argv) as the end.

The code below is tested among G++11, G++14, G++17, Clang++17. For all users including MSVC, use ... instead of args... and __VA_ARGS__ instead of args.

#include <tuple>
#include <cassert>
using namespace std;
#define numargs(args...) tuple_size<decltype(make_tuple(args))>::value
#define argi(i, args...) get<i>(make_tuple(args))
#define rep(i, args...) for (int i = ((numargs(args) > 1) ? argi(0, args) : 0); i < argi(numargs(args) - 1, args); ++i)
#define repi(args...) rep(i, args)

int main() {
    int s = 0;
    repi(5) s += i;
    rep(i, -4, 5) s += i;
    assert(s == 10);
    return 0;
}

By the way, I'm using #define pb(args...) push_back(args) instead of #define pb push_back

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