Question

I am trying to read a file in a specific file format in c.
the file contains some data items. every data item is seprated by a flag.
the file should look look like this:

file-header: "FIL0"
file-id: 0x1020304

flag : 0|1 : uint8_t
length : uint32_t
char[length] : int utf-8

so its: [File-Header] [FileID] [Flag | Length | Data ] [Flag | Length | Data] ...

--> "FIL0" | 0xFFFFFF | 0 or 1 | Data as char[] | 0 or 1 | ... (next data item) ....

My Problem occurs when reading in the file. My idea is to open the file and scan through it using some sscanf-magic.

FILE *fp;
fp = fopen("data.dat". "r");
/* scan file for data components */

  while (fgets(buffer, sizeof buffer, fp) != NULL) /* read in file */
    {
      /* scan for sequence */
      if (sscanf(buffer, "%5s", fil0_header) == 1) /* if the "FIL0" header is found */
        {
          printf("FIL0-header found: %s\n", buffer);

          // proceed and scan for [FLAG] [LENGTH] [DATA]
          // sscanf() 
          if (sscanf(buffer, "%u", node) == 1) 
            {
               // doesnt seem to work 
            }

          // read in length of string and extract stringdata

      else
        {
          printf("FIL0-Header not found, found instead: %s\n", buffer);
          // do something
        }
    }

My problem that I have a hard time with my buffer and the varying data types in the file.

The comparision of fil0-header works alright, but:

• how to read in the next hexadeciaml number (sscanf using %D)
• how scan for the flag which is 1 byte
• how to extract the length which is 4 bytes

A problem is, that the check for the flag starts at the beginning of the buffer.
but the pointer should be moved on, after the FIL0-header is found.
I’d be gratefull for any help!

Please help me to find the proper sscanf() -calls:

and want to read it in and retrieve the single parts of my file:
On single [File-Header]
and many {[FileID] [Flag | Length | Data ]} {…} items

Answer 1

well you could just read the file per byte using

 line[0] = (char) fgetc(fp);
 line[1] = (char) fgetc(fp);

and so on or leave out the cast to retrieve an int-value… should do the trick to do an easy right to left scan of the file (or line – as you say there arent any line breaks)…