用于压缩的缓冲区的 zlib c++ char 大小

Question

我正在使用此函数进行 zlib 压缩，想知道是否应将 outbuffer 变量设置为特定大小？它是否将 char 数组限制为我在此处放置的任何内容？我可以放在这里的长度有限制吗？将它转换为 std::string 是否有意义，因为我是用 C++ 编译的？

 /** Compress a STL string using zlib with given compression level and return
     * the binary data. */
    std::string compress_string(const std::string& str, int compressionlevel = 9)
    {
        z_stream zs;                        // z_stream is zlib's control structure
        memset(&zs, 0, sizeof(zs));

        if (deflateInit(&zs, compressionlevel) != Z_OK)
            throw(std::runtime_error("deflateInit failed while compressing."));

        // For the compress
        deflateInit2(&zs, compressionlevel, Z_DEFLATED,MOD_GZIP_ZLIB_WINDOWSIZE + 16,MOD_GZIP_ZLIB_CFACTOR,Z_DEFAULT_STRATEGY) != Z_OK;

        zs.next_in = (Bytef*)str.data();
        zs.avail_in = str.size();           // set the z_stream's input

        int ret;
        char outbuffer[3222768];
        std::string outstring;

        // retrieve the compressed bytes blockwise
        do {
            zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
            zs.avail_out = sizeof(outbuffer);

            ret = deflate(&zs, Z_FINISH);

            if (outstring.size() < zs.total_out) {
                // append the block to the output string
                outstring.append(outbuffer,zs.total_out - outstring.size());
            }
        }
        while (ret == Z_OK);

        deflateEnd(&zs);

        if (ret != Z_STREAM_END) {          // an error occurred that was not EOF
            std::ostringstream oss;
            oss << "Exception during zlib compression: (" << ret << ") " << zs.msg;
            throw(std::runtime_error(oss.str()));
        }

        return outstring;
    }

Answer 1

这就是 deflateBound() 的用途。在你 deflateInit2() 之后，你可以用输入大小调用它，它会给你在压缩不可压缩数据时可能扩展的限制。

顺便说一句，在同一个结构上调用deflateInit/deflateInit2两次会导致大量内存泄漏。只需调用其中之一即可。

您应该完整阅读 zlib documentation。

用于压缩的缓冲区的 zlib c++ char 大小

zlib c++ char size of buffer for compression

c++

char

zlib