Спринт 6. Связь потоков: в поисках оптимального ввода и вывода.

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log_duration.h
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#pragma once

#include <chrono>
#include <iostream>

using namespace std;
using namespace chrono;
using namespace literals;

#define PROFILE_CONCAT_INTERNAL(X, Y) X##Y
#define PROFILE_CONCAT(X, Y) PROFILE_CONCAT_INTERNAL(X, Y)
#define UNIQUE_VAR_NAME_PROFILE PROFILE_CONCAT(profileGuard, __LINE__)
#define LOG_DURATION(x) LogDuration UNIQUE_VAR_NAME_PROFILE(x)

class LogDuration {
public:
    LogDuration(const std::string& id) : id_(id) {
    }

    ~LogDuration() {
        const auto end_time = steady_clock::now();
        const auto dur = end_time - start_time_;
        cerr << id_ << ": "s << duration_cast<milliseconds>(dur).count() << " ms"s << endl;
    }

private:
    const std::string id_;
    const steady_clock::time_point start_time_ = steady_clock::now();
};
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main.cpp
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#include "log_duration.h"

#include <iostream>

using namespace std;

class StreamUntier {
public:
    StreamUntier(istream& stream) : stream_(stream) {
        tied_before_  = stream_.tie(nullptr);
    }
    ~StreamUntier(){
        stream_.tie(tied_before_);
    }

private:
    ostream* tied_before_;
    istream& stream_;
};

int main() {
    LOG_DURATION("\\n with tie"s);

    StreamUntier guard(cin);
    int i;
    while (cin >> i) {
        cout << i * i << "\n"s;
    }

    return 0;
}