Question

我是否使用此函数进行zlib压缩，并想知道是否应将outbuffer变量设置为特定大小？它是否将char数组限制为我放在这里的任何东西？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，因为我在c ++编译？

 /** 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deflateInit2()之后，您可以使用输入大小调用它，它将在压缩不可压缩数据时为您提供可能的扩展限制。

顺便说一下，在同一个结构上调用deflateInit / deflateInit2两次会导致大量的内存泄漏。只需打电话给其中一个。

您应该完整阅读zlib documentation。

zlib c ++用于压缩的缓冲区的char大小

1 个答案: