LZO压缩字符*

Question

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

在示例文件中，我找到了以下代码片段(我已经为我的应用程序对其进行了一点编辑)：

  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。

我想我需要编辑下面这几行：

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

我在这个变量中有要压缩的字符串：

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

我需要将它转换为其他类型吗？

LZO的文档不是很有用(或者我只是不能正确地使用它)。

Answer 1

主要有三点混淆：

当指针指向的缓冲区不是以结尾的字符串时，最好不要使用

1. *，因为这会让人感到困惑。
2. strlen()只会给出一个以空结尾的字符串的长度，而不会给出内存中任意缓冲区的大小。您需要从其他地方获取该信息。
3. 您传递给lzo1x_1_compress()的缓冲区实际上需要包含您要压缩的数据，而不是一个充满零的空缓冲区。

假设您可以使用imageIn->getFrameSizeBytes()这样的方法从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;
  }

别忘了释放wrkmem。更好的是，使用C++和std::vector作为工作内存，这样它就会自动释放。

Answer 2

getFrame()返回什么类型？为什么需要将其转换为char*？最明显的问题是在二进制数据上使用strlen() -- strlen在遇到第一个零字节时停止。