LZO compress char *

Question

我在我的Ubuntu機器上安裝了LZO，我想用ti來壓縮char *類型的字符串。

在這個例子中的文件，我發現這個代碼片斷（我已經編輯它只是一點點我的應用程序）：

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; 
    } 

但它所做的只是填零。我需要壓縮一個char *變量。

我想我需要編輯這些行：

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

我有我想在這個變量來壓縮字符串：

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

我需要將它轉換爲其他類型？

LZO的文檔不是很有幫助（或者我不能正確使用它）。

Answer 1

有困惑的三個要點：

1. 最好不要使用字符*當 緩衝指針指向是 不是一個空結束的字符串，因爲它是 混亂。
2. strlen（）只會給你 一個以空字符結尾的字符串的長度， 它不會給你一個內存中任意緩衝區大小的 。您需要 才能在其他地方獲取該信息。
3. 傳遞給 lzo1x_1_compress（）實際上需要 緩衝區包含 全是零，你想 壓縮數據，而不是一個空的緩衝區。

假設你可以使用類似imageIn-> getFrameSizeBytes（）讓您的圖像從imageIn大小，試試這個：

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; 
    } 

不要忘記釋放wrkmem。更好的是，使用C++和std :: vector作爲工作內存，以便自動釋放它。

Answer 2

getFrame（）返回什麼類型？你爲什麼需要將它投射到char*？最明顯的問題是在二進制數據上使用strlen() - strlen在遇到第一個零字節時停止。