Question

我在我的Ubuntu机器上安装了LZO，我想用ti来压缩char *类型的字符串。

在示例文件中，我找到了这段代码片段（我已经为我的应用程序编辑了一点）：

  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;
  }

但它的作用是填充零。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);

我想在这个变量中压缩字符串：

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

我是否需要将其转换为其他类型？

LZO的文档不是很有帮助（或者我可能无法正确使用它）。

Answer 1

getFrame（）返回什么类型？为什么需要将其投射到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。

Answer 2

有三个主要的混淆点：

最好不要使用char * 缓冲区指针指向的是不是以空字符结尾的字符串混乱。
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这些信息。
您传递给的缓冲区 lzo1x_1_compress（）实际需要包含您想要的数据压缩而不是空缓冲区满满的零。

假设你可以使用imageIn-＆gt; getFrameSizeBytes（）之类的东西从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，使用C ++和std :: vector作为工作内存，以便自动释放。

LZO压缩炭*

2 个答案: