Thread: Jpeg header

I just start learning C the hard way and i am new to this forum and i hope to
get some advice or if i 'm the right direction.

this the main.c file

Code:

#include <stdio.h>
#include <stdlib.h>
#include <byteswap.h>
#include <stdint.h>
#include "jpeg.h"

enum types {
    PDF,
    JPEG,
    PNG,
    GIF,
    INVALID
};

typedef enum types format;

format checkFormat(FILE *fd, const uint8_t buffer[]){
   if( fd == NULL){
      printf("Invalid file format");
}
   switch (buffer[0]){
      case 0x25:
         printf(" PDF \n");
         return PDF;
      case 0x89:
         printf(" PNG \n");
         return PNG;
      case 0x47:
         printf(" GIF \n");
         return GIF;
     case 0xFF:
         printf(" JPEG \n");
         return JPEG;
     default:
         return INVALID;
}
}

int main(int argc, char *argv[]) {
     FILE *fd;
      long fdSize;
      uint8_t *buffer;

      printf("Enter file path:");

     fd = fopen(argv[1], "rb");
     if ( fd == NULL )
    {
        perror("Unable to open the file");
        exit(EXIT_FAILURE);
    }
   fseek(fd, 0L, SEEK_END);
    fdSize = ftell(fd);
 
/* reset the file position indicator to the beginning of the file */
fseek(fd, 0L, SEEK_SET);

buffer = (uint8_t*)calloc((size_t) fdSize, sizeof(uint8_t));
/* memory error */
if(buffer == NULL)
      return 1;

/* copy all the text into the buffer */
fread(buffer, sizeof(uint8_t), (size_t) fdSize, fd);
fclose(fd);
/* fm for later use*/
format fm = checkFormat(fd, (const uint8_t *) buffer);
parseHeader(buffer);
free(buffer);
return 0;
}

jpeg.h file

Code:

#include <stdint.h>

#ifndef FILE_DECODER_JPEG_H
#define FILE_DECODER_JPEG_H

#endif //FILE_DECODER_JPEG_H
typedef struct JHeader {
  uint16_t SIO;               
   uint16_t APP0;         
   uint16_t Lenght;         
   uint32_t ID;                      
   uint16_t VERSION;     
   uint16_t Xdensity;          
   uint16_t Ydensity;       
   uint16_t XThumbnail;     
   uint16_t YThumbnail;     
}JHeader;

JHeader parseHeader(uint8_t *buffer);
uint32_t slice(int start, int end, uint8_t *buffer);

jpeg.c file

Code:

#include <stdio.h>
#include <memory.h>
#include <stdint.h>
#include <byteswap.h>
#include "jpeg.h"

JHeader header;

uint32_t slice(int start, int end, uint8_t *buffer){
    uint32_t a;
    unsigned int i = 0;
    uint8_t sl[16];

while(start <= end){
      sl[i] = buffer[start];
      start++;
      i++;
}
   memcpy(&a, sl, sizeof(unsigned int));
   return a;
}

JHeader parseHeader(uint8_t *buffer) {
 header.SIO = bswap_16(slice(0,2, buffer));
  header.APP0 = bswap_16(slice(2,3, buffer));
  header.Lenght = bswap_16(slice(4,5, buffer));
  header.ID = bswap_32(slice(6,9, buffer));
  header.VERSION = bswap_16(slice(11,13, buffer));
  header.Xdensity = bswap_16(slice(14,15, buffer));
  header.Ydensity = bswap_16(slice(16,17, buffer));
  header.XThumbnail = buffer[18];
  header.YThumbnail = buffer[19];
  printf("start of image %x\n", header.SIO);
  printf("APP0 marker %x\n", header.APP0);
  printf("Length %x\n", header.Lenght);
  printf("Identifier %x\n", header.ID);
  printf("Version %x\n", header.VERSION);
  printf("X density %x\n", header.Xdensity);
  printf("Y density %x\n", header.Ydensity);
  printf("X thumbnail %x\n", header.XThumbnail);
  printf("Y thumbnail %x\n", header.YThumbnail);

  return header;
}

You are using magic numbers

Code:

switch (buffer[0]){
      case 0x25:
         printf(" PDF \n");
         return PDF;
      case 0x89:
         printf(" PNG \n");
         return PNG;
      case 0x47:
         printf(" GIF \n");
         return GIF;
     case 0xFF:
         printf(" JPEG \n");
         return JPEG;
     default:
         return INVALID;

Your indentation is off - Each of your line's starting point is inconsistant. I had to look twice to notice that there are two functions there...

Choose one indentation style and stick to it - Styles - I use Allman, because I do a lot of C# on visual studio. If you want to programme for a job, then you'll need to follow the style that they use.


You may want to check argc to see if the user has entered the correct thing - If they did not, quickly prompt them


Don't cast the return value of collac unless you are compiling for C++. See here


Every use of "fdSize" is cast to size_t - Why not just define it as type size_t?

Originally Posted by Click_here

I use Allman, because I do a lot of C# on visual studio.

I use Allman style too, and some other options for astyle (F2, normal mode keymap, on my VIM):

Code:

" C style formater
map <F2> :%!astyle --mode=c -A1 -s2 -xc -xj -f -p -D -k3 -xd -xW -xV -L -p -xg -P -H -y -xb -xj -xf -w -c -U -S <CR>

Cross-posted here -> Jpeg Header - C And C++ | Dream.In.Code

the indentation is actually i copied directly without fixing it, i use linux style 8 indentation, i really appreciate guys your opinions it really helping me fix my issues that i couldn't see on my own