c++ - Reading BMP file C++(读取BMP文件头有问题)

Question

我正在尝试用读取方法编写 BMP 图像类。我看到了 BMP 文件的 msdn 规范，所以我尝试读取标题，然后使用 biHeight 和 biWidth 信息读取每个像素的 RGB 信息。所以，它不读取头信息，每个头参数的值都是-1。

代码如下:

#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;
        }
}

附言谢谢大家的帮助

Answer 1

成员

ifstream pFile;

类 BMPImage 没有被初始化，所以当你在成员函数中使用它时它是无效的。相反，您在构造函数中本地定义了一个不同的 pFile 实例。这些可能应该是同一个实例。