How Can I Efficiently Write to a Specific Buffer Using a Stringstream in C ?

Configuring a Stream to Write to a Specific Buffer

When writing data to an existing buffer using the stringstream class, it's important to avoid excessive copying. The default mechanism involves copying the message from the stream to a temporary string object, which can be inefficient.

Original Approach and Its Limitations

Initially, an attempt was made to use the rdbuf()->pubsetbuf() method to redirect the stream output to the desired buffer. However, this method proved ineffective in the Visual Studio 2008 implementation.

Custom Streambuf Implementation

A viable alternative is to create a custom std::streambuf class that initializes its internal pointers to refer to the supplied buffer:

template <typename char_type>
struct ostreambuf : public std::basic_streambuf<char_type, std::char_traits<char_type>>
{
    ostreambuf(char_type* buffer, std::streamsize bufferLength)
    {
        setp(buffer, buffer + bufferLength);
    }
};

Revised Code Using Custom Streambuf

Using the custom ostreambuf type, the code is rewritten as follows:

void FillBuffer(char* buffer, unsigned int size)
{
    ostreambuf<char> ostreamBuffer(buffer, size);
    std::ostream messageStream(&ostreamBuffer);

    messageStream << "Hello" << std::endl;
    messageStream << "World!" << std::endl;
}

Now, data is written directly to the external buffer without unnecessary copying. This approach provides greater efficiency and flexibility when working with buffers.

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