在C ++中读取BMP文件的所有字节并旋转图片

Question

I have a BMP file. I want to read all of its characters and rotate 90 cw the picture by these codes. But this codes works only on small pictures and colors were changed. I want use this codes for 800*686 pixels picture. this codes doesn't work for it. I think error is in reading file, because when I check the char vector of input file, after 59000 bytes, all of the chars in vector filled by 0 and the file didn't read compeletely:

struct pixel
{   char blue;
    char green;
    char red;
};

int _tmain(int argc, _TCHAR* argv[])
{

        //Reading file and save all into data vector
        fstream fl("d://b.bmp");
        ofstream fl2("d://b2.bmp");
        fl.seekg(0,std::ios::end);
        streampos  length = fl.tellg();
        vector<char>  data(length);
        fl.seekg(0,ios::beg);
        fl.read(&data[0],length);


    //make a string of bytes based on characters in "file" vector ,to calculate file features
        byte intfile[54];
        for(int i=0;i<54;i++)
        {
            if (data[i]<0)
                intfile[i]=(256+data[i]);
            else
                intfile[i]=data[i];
        }

        //bpp is 2 bytes on 28,29 characters
        short int bpp = intfile[28] | intfile[29] << 8;

        //size of file is 4 bytes on 2,3,4,5 characters
        unsigned int size= intfile[2] | intfile[3] << 8 | intfile[4] << 16 | intfile[5] << 24;

        //offset of pixeles array is 4 bytes on 10,11,12,13 characters
        unsigned int offset= intfile[10] | intfile[11] << 8 | intfile[12] << 16 | intfile[13] << 24;

        //with is 4 bytes on 18,19,20,21 characters
        unsigned int with= intfile[18] | intfile[19] << 8 | intfile[20] << 16 | intfile[21] << 24;

        //height is 4 bytes on 22,23,24,25 characters
        unsigned int height= intfile[22] | intfile[23] << 8 | intfile[24] << 16 | intfile[25] << 24;

        //format of compression is 4 bytes on 30,31,32,33 characters
        unsigned int format= intfile[30] | intfile[31] << 8 | intfile[32] << 16 | intfile[33] << 24;


        //2D vector of pixels and filling it by data vector
        vector< vector<pixel> > arrpix;
        arrpix.resize(height);
        for(int j=0;j<height;j++)
            arrpix[j].resize(with);

        int ix=offset;
        for(int i=0;i<height;i++){
            for(int j=0;j<with;j++){
                arrpix[i][j].blue=data[ix++]; 
                arrpix[i][j].green=data[ix++];
                arrpix[i][j].red=data[ix++]; 
            }
            ix+=2;//padd
        }

        //2d new vector for making new rotated file
        vector< vector<pixel> > arrpix2;
        arrpix2.resize(with);
        for(int j=0;j<with;j++)
            arrpix2[j].resize(height);

        for(int i=0;i<with;i++)
            for(int j=0;j<height;j++){
                arrpix2[i][j].blue=arrpix[j][with-1-i].blue;
                arrpix2[i][j].green=arrpix[j][with-1-i].green;          
                arrpix2[i][j].red=arrpix[j][with-1-i].red;
            }   

        //newsize
        unsigned int news=(with*height*3)+54;//in rotation pad is not need because the new with is 800

        //makeing new vector
        vector<char>  data2(news);
        for(int i=0;i<news;i++)
            data2[i]=data[i];

        //change size
        data2[5] = (news >> 24) & 0xFF;
        data2[4] = (news >> 16) & 0xFF;
        data2[3] = (news >> 8) & 0xFF;
        data2[2] = news & 0xFF;


        //replace height and with
        for(int i=0;i<4;i++){
            data2[18+i]=data[22+i];
            data2[22+i]=data[18+i];}
        ix=offset;
        //filling data by 2d new vector
        for(int i=0;i<with;i++){
            for(int j=0;j<height;j++){
                data2[ix++]=arrpix2[i][j].blue;
                data2[ix++]=arrpix2[i][j].green;
                data2[ix++]=arrpix2[i][j].red;
            }   
        }


        fl2.write(&data2[0],news);
        fl2.seekp(news,ios::beg);
        fl2.close();


    return 0;
}

Answer 1

When you reposition the file back to the beginning, to actually read the data I think you want:

 fl.seekg(0,ios::beg);

rather than

 fl.seekg(length,ios::beg);

edit:

After the read add this code:

if(f1.eof())
{
   std::cerr << "Error reading file."
             << " Requested " << length << " bytes."
             << " Read " << f1.gcount() << bytes."
             << std::endl;
}

That should tell you how big your code thinks the file is (verify against actual file size), and whether f1 thinks the read went well.

---

Also you should open the file in binary mode by using the ios::binary mode flag when you open the file.