How to Capture Standard Output and Error Streams in a String in C ?

How to Redirect Output to a String in C

For various debugging and testing scenarios, it can be convenient to redirect the standard output and error streams to a string rather than to the console.

Solution: Using std::stringstream

To redirect stdout/stderr to a string, you can utilize the std::stringstream class:

<code class="cpp">std::stringstream buffer;
std::streambuf *old = std::cout.rdbuf(buffer.rdbuf());

std::cout << "Bla" << std::endl;

std::string text = buffer.str(); // text will now contain "Bla\n"</code>

Guard Class for Buffer Reset

To ensure that the buffer is reset after redirecting, you can create a guard class:

<code class="cpp">struct cout_redirect {
    cout_redirect(std::streambuf *new_buffer) : old(std::cout.rdbuf(new_buffer)) {}

    ~cout_redirect() { std::cout.rdbuf(old); }

private:
    std::streambuf *old;
};</code>

This guard class guarantees that the buffer is always restored to its original state, even in the event of exceptions.

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