CODEWITHSUNDEEP
cbmp
ROO0110
ROO0110

Reputation: 21

I can't reach the size of header of BMP file in c code

I want to copy a 1bit BMP image and I wrote this code. I don't know why the size of Header struct in my code is 56, although it need to be 54.

My code for struct HeaderBMP:



      short _type;    // file type
      short _size;
    int _reserved;
       int _offset;

        int  _info_size;
        int _width;
        int _height;

        short _planes;
        short _bpp;

        int _compression;
        int _imagesize;

        int _xresolution;
        int _yresolution;

        int _colours;
        int _impcolours;

I can't reach to size 54, it is just 52 or 56 when I try to fix . I hope you can help me to fix this.

Upvotes: 0

Views: 207

Answers (2)

ROO0110
ROO0110

Reputation: 21

Thank you for your solution, however its is also 56 when I compile by passing argument through cmd on window 10 x64. It is 54 when it works on ubuntu and codeblock on window with passing argument in code. My solution :

typedef struct {             // Total: 54 bytes
   char  _type[2];             // Magic identifier: 0x4d42
  char  _size[4];             // File size in bytes
  char _reserved1[2];        // Not used
  char  _reserved2[2];        // Not used
  char _offset[4];           // Offset to image data in bytes from beginning of file (54 bytes)
  char  _dib_header_size[4];  // DIB Header size in bytes (40 bytes)
  char   _width[4];         // Width of the image
  char   _height[4];        // Height of image
  char _planes[2];       // Number of color planes
  char  _bpp[2];   // Bits per pixel
  char _compression[4];      // Compression type
  char  _image_size[4]; // Image size in bytes
  char   _x_resolution_ppm[4]; // Pixels per meter
  char   _y_resolution_ppm[4]; // Pixels per meter
  char _num_colors[4];       // Number of colors
  char  _important_colors[4]; // Important colors
}  header;

and when I need to take value , I will do :

    *(int*) header._width

I test and it works with above three cases .

Upvotes: 0

0___________
0___________

Reputation: 67476

Use fixed size integers for this kind of structs. Those types are defined in the stdint.h header file. struct might require packing (which is implementation defined)

gcc example:

typedef struct {             // Total: 54 bytes
  uint16_t  type;             // Magic identifier: 0x4d42
  uint32_t  size;             // File size in bytes
  uint16_t  reserved1;        // Not used
  uint16_t  reserved2;        // Not used
  uint32_t  offset;           // Offset to image data in bytes from beginning of file (54 bytes)
  uint32_t  dib_header_size;  // DIB Header size in bytes (40 bytes)
  int32_t   width_px;         // Width of the image
  int32_t   height_px;        // Height of image
  uint16_t  num_planes;       // Number of color planes
  uint16_t  bits_per_pixel;   // Bits per pixel
  uint32_t  compression;      // Compression type
  uint32_t  image_size_bytes; // Image size in bytes
  int32_t   x_resolution_ppm; // Pixels per meter
  int32_t   y_resolution_ppm; // Pixels per meter
  uint32_t  num_colors;       // Number of colors  
  uint32_t  important_colors; // Important colors 
} __attribute__((packed)) BMPHeader;

Upvotes: 2

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