c++ - LZO 压缩字符*

Question

我已经在我的 Ubuntu 机器上安装了 LZO，我想使用 ti 来压缩一个 char* 类型的字符串。

在示例文件中，我找到了这个代码片段(我已经为我的应用程序对它进行了一些编辑):

  int r;
  lzo_bytep in;
  lzo_bytep out;
  lzo_voidp wrkmem;
  lzo_uint in_len;
  lzo_uint out_len;
  lzo_uint new_len;
  int strToCompressLen; // I have added this

  /*
   * Step 1: initialize the LZO library
   */
  if (lzo_init() != LZO_E_OK)
  {
    cout << "internal error - lzo_init() failed !!!" << endl;
    cout << "(this usually indicates a compiler bug - try recompiling\nwithout optimizations, and enable '-DLZO_DEBUG' for diagnostics)" << endl;
    //return 4;
  }

  // here I get the data I want to compress
  char* imageData = (char*)imageIn->getFrame();

  /*
   * Step 2: allocate blocks and the work-memory
   */
  strToCompressLen = strlen(imageData);
  in = (lzo_bytep) xmalloc(strToCompressLen);
  out = (lzo_bytep) xmalloc((strToCompressLen + strToCompressLen / 16 + 64 + 3));
  wrkmem = (lzo_voidp) xmalloc(LZO1X_1_MEM_COMPRESS);
  if (in == NULL || out == NULL || wrkmem == NULL)
  {
        cout << "out of memory" << endl;
        //return 3;
  }

  /*
   * Step 3: prepare the input block that will get compressed.
   *         We just fill it with zeros in this example program,
   *         but you would use your real-world data here.
   */
  in_len = strToCompressLen;
  lzo_memset(in,0,in_len);

  /*
   * Step 4: compress from 'in' to 'out' with LZO1X-1
   */
  r = lzo1x_1_compress(in,in_len,out,&out_len,wrkmem);
  if (r != LZO_E_OK)
  {
        /* this should NEVER happen */
        cout << "internal error - compression failed: " << r << endl;
        //return 2;
  }
  /* check for an incompressible block */
  if (out_len >= in_len)
  {
        cout << "This block contains incompressible data." << endl;
    //return 0;
  }

但它所做的只是填充零。我需要压缩一个 char* 变量。

我想我需要编辑这些行:

  in_len = strToCompressLen;
  lzo_memset(in,0,in_len);

我在这个变量中有我想要压缩的字符串:

  char* imageData = (char*)imageIn->getFrame();

我需要将其转换为其他类型吗？

LZO 的文档不是很有帮助(或者我可能无法正确使用它)。

Answer 1

主要有3个混淆点:

1. 最好不要使用 char* 当指针指向的缓冲区是不是一个以 null 结尾的字符串令人困惑。
2. strlen() 只会给你以 null 结尾的字符串的长度，它不会给你一个大小内存中的任意缓冲区。你需要在其他地方获取该信息。
3. 你传递给的缓冲区lzo1x_1_compress() 实际上需要包含你想要的数据压缩而不是空缓冲区全是零。

假设您可以使用 imageIn->getFrameSizeBytes() 之类的方法从 imageIn 获取图像的大小，试试这个:

  int r;
  lzo_bytep out;
  lzo_voidp wrkmem;
  lzo_uint out_len;
  lzo_uint new_len;

  /*
   * Step 1: initialize the LZO library
   */
  if (lzo_init() != LZO_E_OK)
  {
    cout << "internal error - lzo_init() failed !!!" << endl;
    cout << "(this usually indicates a compiler bug - try recompiling\nwithout optimizations, and enable '-DLZO_DEBUG' for diagnostics)" << endl;
    //return 4;
  }

  // here I get the data I want to compress
  lzo_bytep imageData = (lzo_bytep) imageIn->getFrame();
  size_t uncompressedImageSize = imageIn->getFrameSizeBytes();

  /*
   * Step 2: allocate blocks and the work-memory
   */
  out = (lzo_bytep) xmalloc((uncompressedImageSize + uncompressedImageSize / 16 + 64 + 3));
  wrkmem = (lzo_voidp) xmalloc(LZO1X_1_MEM_COMPRESS);
  if (out == NULL || wrkmem == NULL)
  {
        cout << "out of memory" << endl;
        //return 3;
  }

  /*
   * Step 4: compress from 'imageData' to 'out' with LZO1X-1
   */
  r = lzo1x_1_compress(imageData,uncompressedImageSize,out,&out_len,wrkmem);
  if (r != LZO_E_OK)
  {
        /* this should NEVER happen */
        cout << "internal error - compression failed: " << r << endl;
        //return 2;
  }

  /* check for an incompressible block */
  if (out_len >= uncompressedImageSize)
  {
        cout << "This block contains incompressible data." << endl;
    //return 0;
  }

不要忘记释放 wrkmem。更好的是，将 C++ 和 std::vector 用于工作内存，以便自动释放它。