C++: Write BMP image format error on WINDOWS -

i have strange problem here... i'm using same code(copy-paste) linux in windows read , write , bmp image. , reason in linux every thing works perfectly fine, when i'm coming windows 10 can't open images , i've receive error message how said this:

"it looks don't support file format."

do have idea should do? put code below.

edit:

i've solved padding problem , it's write images white, idea why? i've update code also.

struct bmp {     int width;     int height;     unsigned char header[54];     unsigned char *pixels;     int size;     int row_padded; };  void writebmp(string filename, bmp image) {     string filename = "output files\\" + filename;     file *out = fopen(filename.c_str(), "wb");     fwrite(image.header, sizeof(unsigned char), 54, out);      unsigned char tmp;     (int = 0; < image.height; i++) {         (int j = 0; j < image.width * 3; j += 3) {             // convert (b, g, r) (r, g, b)             tmp = image.pixels[j];             image.pixels[j] = image.pixels[j + 2];             image.pixels[j + 2] = tmp;         }         fwrite(image.pixels, sizeof(unsigned char), image.row_padded, out);     }     fclose(out); }  bmp readbmp(string filename) {     bmp image;     string filename = "input files\\" + filename;     file *f = fopen(filename.c_str(), "rb");      if (f == null)         throw "argument exception";      fread(image.header, sizeof(unsigned char), 54, f); // read 54-byte header      // extract image height , width header     image.width = *(int *) &image.header[18];     image.height = *(int *) &image.header[22];      image.row_padded = (image.width * 3 + 3) & (~3);     image.pixels = new unsigned char[image.row_padded];     unsigned char tmp;      (int = 0; < image.height; i++) {         fread(image.pixels, sizeof(unsigned char), image.row_padded, f);         (int j = 0; j < image.width * 3; j += 3) {             // convert (b, g, r) (r, g, b)             tmp = image.pixels[j];             image.pixels[j] = image.pixels[j + 2];             image.pixels[j + 2] = tmp;         }     }     fclose(f);     return image;  } 

in point of view code should cross-platform... it's not... why?

thanks help

check header

the header must start following 2 signature bytes: 0x42 0x4d. if it's different third party application think file doesn't contain bmp picture despite .bmp file extension.

the size , way pixels stored little bit more complex expect: assume number of bits per pixels 24 , no no compression used. not guaranteed. if it's not case, might read more data available, , corrupt file when writing back.

furthermore, size of header depends on bmp version using, you can detect using 4 byte integer @ offset 14.

improve code

when load file, check signature, bmp version, number of bits per pixel , compression. debugging purpose, consider dumping header check manually:

for (int i=0; i<54; i++)      cout << hex << image.header[i] << " ";`  cout <<endl;  

furthermore, when fread() check number of bytes read correspond size wanted read, sure you're not working uninitialized buffer data.

edit:

having checked dump, appears format expected. verifying padded size in header padded size have calculated appears error here:

image.row_padded = (image.width * 3 + 3) & (~3);     // ok size of single row rounded multiple of 4 image.pixels = new unsigned char[image.row_padded];  // oops !  little short ?  

in fact read row row, keep last 1 in memory ! different of first version, did read full pixels of picture.

similarly, write last row repeated height time.

reconsider padding, working total padded size.

image.row_padded = (image.width * 3 + 3) & (~3);     // ok size of single row rounded multiple of 4 image.size_padded = image.row_padded * image.height;  // padded full size image.pixels = new unsigned char[image.size_padded];  // yeah !  if (fread(image.pixels, sizeof(unsigned char), image.size_padded, f) !=  image.size_padded) {     cout << "error: bytes couldn't read"<<endl;  } else {      ... // process pixels expected } ...