CaptureStream.hpp

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#pragma once
 
#include <iostream>
#include <sstream>
 
namespace stc::testutil {
 
template <class T, typename = std::enable_if_t<std::is_base_of_v<std::ios_base, T>>>
class CaptureStream {
private:
    T& stream;
    // We need to store the buffer to restore it afterwards
    decltype(stream.rdbuf()) buffer;
 
public:
    std::stringstream content;
 
    [[nodiscard("Discarding the field means all the streams are immediately uncaptured")]]
    CaptureStream(T& stream) : stream(stream) {
        this->buffer = stream.rdbuf();
        this->stream.rdbuf(content.rdbuf());
    }
 
    ~CaptureStream() {
        restore();
    }
 
    void restore() {
        if (buffer != nullptr) {
            stream.rdbuf(buffer);
            buffer = nullptr;
        }
    }
 
    void reset() {
        content = {};
        stream.rdbuf(content.rdbuf());
    }
};
 
struct CaptureStandardStreams {
    CaptureStream<decltype(std::cout)> cout{std::cout};
    CaptureStream<decltype(std::cerr)> cerr{std::cerr};
    CaptureStream<decltype(std::cin)> cin{std::cin};
};
 
}