在C++中實現buffer的壓縮和解壓功能可以使用一些開源的壓縮庫，比如zlib、zstd、LZ4等。這些庫提供了壓縮和解壓縮數據的函數，可以很方便地在C++代碼中調用。

以下是一個使用zlib庫實現buffer壓縮和解壓縮的示例代碼：

#include <iostream>
#include <zlib.h>

// 壓縮函數
void compressData(const char* input, size_t inputSize, char* output, size_t& outputSize)
{
    z_stream stream;
    stream.zalloc = Z_NULL;
    stream.zfree = Z_NULL;
    stream.opaque = Z_NULL;

    if(deflateInit(&stream, Z_BEST_COMPRESSION) != Z_OK)
    {
        return;
    }

    stream.avail_in = inputSize;
    stream.next_in = (Bytef*)input;
    stream.avail_out = outputSize;
    stream.next_out = (Bytef*)output;

    int ret = deflate(&stream, Z_FINISH);
    if(ret != Z_STREAM_END)
    {
        deflateEnd(&stream);
        return;
    }

    deflateEnd(&stream);
    outputSize = stream.total_out;
}

// 解壓函數
void decompressData(const char* input, size_t inputSize, char* output, size_t& outputSize)
{
    z_stream stream;
    stream.zalloc = Z_NULL;
    stream.zfree = Z_NULL;
    stream.opaque = Z_NULL;

    if(inflateInit(&stream) != Z_OK)
    {
        return;
    }

    stream.avail_in = inputSize;
    stream.next_in = (Bytef*)input;
    stream.avail_out = outputSize;
    stream.next_out = (Bytef*)output;

    int ret = inflate(&stream, Z_FINISH);
    if(ret != Z_STREAM_END)
    {
        inflateEnd(&stream);
        return;
    }

    inflateEnd(&stream);
    outputSize = stream.total_out;
}

int main()
{
    const char* input = "Hello, world!";
    size_t inputSize = strlen(input);
    size_t compressedSize = compressBound(inputSize);
    char* compressedData = new char[compressedSize];

    compressData(input, inputSize, compressedData, compressedSize);

    std::cout << "Compressed data size: " << compressedSize << std::endl;

    size_t decompressedSize = inputSize;
    char* decompressedData = new char[decompressedSize];

    decompressData(compressedData, compressedSize, decompressedData, decompressedSize);

    std::cout << "Decompressed data: " << decompressedData << std::endl;

    delete[] compressedData;
    delete[] decompressedData;

    return 0;
}

在上面的示例代碼中，我們使用zlib庫實現了buffer的壓縮和解壓縮功能。在壓縮函數中，我們使用deflateInit()函數初始化z_stream結構體，然后調用deflate()函數進行數據壓縮；在解壓函數中，我們使用inflateInit()函數初始化z_stream結構體，然后調用inflate()函數進行數據解壓。壓縮后的數據可以通過compressBound()函數獲取壓縮后的大小。