Question

我想根据运行时给出的标志使输出详细/非详细。我的想法是，构造一个依赖于标志的std :: ostream，例如：

std::ostream out;
if (verbose) {
    out = std::cout
else {
    // Redirect stdout to null by using boost's null_sink.
    boost::iostreams::stream_buffer<boost::iostreams::null_sink> null_out{boost::iostreams::null_sink()};

    // Somehow construct a std::ostream from nullout
}

现在我不得不从这样的提升streambuffer构建一个std :: ostream。我该怎么做？

Answer 1

使用标准库

只需重置rdbuf：

即可

auto old_buffer = std::cout.rdbuf(nullptr);

否则，只需使用流：

std::ostream nullout(nullptr);
std::ostream& out = verbose? std::cout : nullout;

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#include <iostream>

int main(int argc, char**) {
    bool verbose = argc>1;

    std::cout << "Running in verbose mode: " << std::boolalpha << verbose << "\n";

    std::ostream nullout(nullptr);
    std::ostream& out = verbose? std::cout : nullout;

    out << "Hello world\n";
}

运行./test.exe时：

Running in verbose mode: false

运行./test.exe --verbose时：

Running in verbose mode: true
Hello world

使用Boost Iostreams

如果你坚持的话，你/当然可以使用Boost IOstream：

请注意，根据评论，这绝对更好，因为流不会出现在＆＃34;错误＆＃34;一直都在说。

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#include <iostream>
#include <boost/iostreams/device/null.hpp>
#include <boost/iostreams/stream.hpp>

int main(int argc, char**) {
    bool verbose = argc>1;

    std::cout << "Running in verbose mode: " << std::boolalpha << verbose << "\n";

    boost::iostreams::stream<boost::iostreams::null_sink> nullout { boost::iostreams::null_sink{} };
    std::ostream& out = verbose? std::cout : nullout;

    out << "Hello world\n";
}

如何使用boost :: iostreams :: null_sink作为std :: ostream

1 个答案:

使用标准库

使用Boost Iostreams