閱讀BMP文件C++（閱讀BMP標題時遇到的問題）

Question

我正在嘗試使用閱讀方法編寫BMP圖像類。我看到了BMP文件的msdn規範，所以我嘗試讀取頭文件，之後使用biHeight和biWidth信息讀取每個像素的RGB信息。 所以，它不讀取標題信息，每個標題參數的值是-1。

這裏是代碼：

#ifndef BMP_IMAGE_H 
#define BMP_IMAGE_H 

#include <fstream> 

using namespace std; 


typedef struct 
{ 
    unsigned int bfType; 
    unsigned long bfSize; 
    unsigned int bfReserved1; 
    unsigned int bfReserved2; 
    unsigned long bfOffBits; 
} BitMapFileHeader; 

typedef struct 
{ 
    unsigned int biSize; 
    int    biWidth; 
    int    biHeight; 
    unsigned short biPlanes; 
    unsigned short biBitCount; 
    unsigned int biCompression; 
    unsigned int biSizeImage; 
    int    biXPelsPerMeter; 
    int    biYPelsPerMeter; 
    unsigned int biClrUsed; 
    unsigned int biClrImportant; 
} BitMapInfoHeader; 

typedef struct 
{ 
    int rgbBlue; 
    int rgbGreen; 
    int rgbRed; 
    int rgbReserved; 
} RGBColor; 


class BMPImage 
{ 
private: 
    unsigned short read_u16(); 
    unsigned int read_u32(); 
    int   read_s32(); 
public: 
    ifstream pFile; 
    int imageWidth; 
    int imageHeight; 
    RGBColor **rgb; 
    BMPImage(char* fileName); 
    void pixelsInfo(); 
}; 

#endif // BMP_IMAGE_H 

#include "bmp_image.h" 
#include <iostream> 
using namespace std; 
BMPImage::BMPImage(char* fileName) 
{ 
    ifstream pFile(fileName, ios::in | ios::binary); 


    // read the header of file 
    BitMapFileHeader header __attribute__((unused)); 

    header.bfType  = read_u16(); 
    header.bfSize  = read_u32(); 
    header.bfReserved1 = read_u16(); 
    header.bfReserved2 = read_u16(); 
    header.bfOffBits = read_u32(); 

    // read the header of image 
    BitMapInfoHeader bmiHeader; 

    bmiHeader.biSize   = read_u32(); 
    bmiHeader.biWidth   = read_s32(); 
    bmiHeader.biHeight  = read_s32(); 
    bmiHeader.biPlanes  = read_u16(); 
    bmiHeader.biBitCount  = read_u16(); 
    bmiHeader.biCompression = read_u32(); 
    bmiHeader.biSizeImage  = read_u32(); 
    bmiHeader.biXPelsPerMeter = read_s32(); 
    bmiHeader.biYPelsPerMeter = read_s32(); 
    bmiHeader.biClrUsed  = read_u32(); 
    bmiHeader.biClrImportant = read_u32(); 

    cout << (int)bmiHeader.biHeight <<"\n"; 
    RGBColor **rgb = new RGBColor*[bmiHeader.biHeight]; 
    for (int i = 0; i < bmiHeader.biWidth; i++) 
      rgb[i] = new RGBColor[bmiHeader.biHeight]; 

    for (int i = 0; i < bmiHeader.biWidth; i++) { 
     for (int j = 0; j < bmiHeader.biHeight; j++) { 
      rgb[i][j].rgbBlue = pFile.get(); 
      rgb[i][j].rgbGreen = pFile.get(); 
      rgb[i][j].rgbRed = pFile.get(); 


     } 


     char temp; 
     pFile.get(temp); 
     } 

    imageWidth = bmiHeader.biWidth; 
    imageHeight = bmiHeader.biHeight; 

    pFile.close(); 
} 

unsigned short BMPImage::read_u16(){ 
    unsigned char b0, b1; 
    b0 = pFile.get(); 
    b1 = pFile.get(); 

    return ((b1 << 8) | b0); 
} 

unsigned int BMPImage::read_u32(){ 
    unsigned char b0, b1, b2, b3; 
    b0 = pFile.get(); 
    b1 = pFile.get(); 
    b2 = pFile.get(); 
    b3 = pFile.get(); 

    return ((((((b3 << 8) | b2) << 8) | b1) << 8) | b0); 
} 

int BMPImage::read_s32(){ 
     unsigned char b0, b1, b2, b3; 
     b0 = pFile.get(); 
     b1 = pFile.get(); 
     b2 = pFile.get(); 
     b3 = pFile.get(); 
     return ((int)(((((b3 << 8) | b2) << 8) | b1) << 8) | b0); 

} 

void BMPImage::pixelsInfo(){ 
    for (int i = 0; i < imageWidth; i++) { 
      for (int j = 0; j < imageHeight; j++) { 
       std::cout << rgb[i][j].rgbRed <<" " << rgb[i][j].rgbGreen << " " << rgb[i][j].rgbBlue << std::endl; 
      } 
      std::cout << std::endl; 
     } 
} 

附：謝謝大家的幫助

Answer 1

成員

ifstream pFile; 

類BMPImage未被初始化的

，所以當你在成員函數使用它，它是無效的。而是在本地在構造函數中定義一個不同的pFile實例。這些應該可能是同一個實例。

Answer 2

我想你應該改變這樣的：

typedef struct 
{ 
    int rgbBlue; 
    int rgbGreen; 
    int rgbRed; 
    int rgbReserved; 
} RGBColor; 

對於這一點：

typedef struct 
{ 
    unsigned char rgbBlue; 
    unsigned char rgbGreen; 
    unsigned char rgbRed; 
    unsigned char rgbReserved; 
} RGBColor; 

參考：https://msdn.microsoft.com/en-us/library/windows/desktop/dd162938(v=vs.85).aspx