Extract sequences of bytes from binary for differents blocks Post: 302843792

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Top Forums Shell Programming and Scripting Extract sequences of bytes from binary for differents blocks Post 302843792 by ahamed101 on Thursday 15th of August 2013 06:16:29 AM

08-15-2013

Registered User

Well, there is nothing which mentions the end of each block. 0xff 0x33 represents the end of file, is that right?

Following code extracts the data from which you want, but there is no check for end of block as I am still confused. May be a larger file with expected output can clarify it.

Code:

#include <stdio.h>
#include <stdlib.h>

#define err(x) {printf("\nError: %s... Exiting...\n", x); exit(1);}

static unsigned char pat1[] = {0x99, 0x11, 0x45, 0x27};
static unsigned char pat2[] = {0x73, 0x49};

int main(int argc, char **argv)
{

        if(argc < 2)
                err("File name missing");

        unsigned char buf[32];
        unsigned char *ptr = buf;
        int pos = 0;

        FILE *fp = fopen(argv[1], "rb");
        if(!fp) err("Unable to open the file");

        while(!feof(fp)){
                fread(ptr, sizeof(char), 1, fp);
                pos = ftell(fp);
                if(buf[0] == 0x32){
                        fread(ptr+1, sizeof(char), 19, fp);
                        if(memcmp(buf+4, pat1, 4) && memcmp(buf+12, pat2, 2)){
                                fseek(fp, pos, SEEK_SET);
                                continue;
                        }else{
                                int i=0;
                                for(i=0;i<=19;i++) printf("%02x ", buf[i]);
                                printf("\n");
                        }
                }
        }
        return 0;
}

Code:

user@Imperfecto_:~$ gcc extract.c -o extract 
user@Imperfecto_:~$ ./extract binfile.txt 
32 00 00 01 99 11 45 27 89 34 55 0f 73 49 45 49 23 2f ff ff 
32 00 00 02 99 11 45 27 89 34 55 1f 73 49 45 54 76 8f ff ff 
user@Imperfecto_:~$

--ahamed

---------- Post updated at 03:16 AM ---------- Previous update was at 03:13 AM ----------

Or is it that once we encounter 0xff 0x33, we should stop?

--ahamed

Last edited by ahamed101; 08-15-2013 at 08:05 AM..

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LEARN ABOUT DEBIAN

sdl_audiocvt

SDL_AudioCVT(3) 						 SDL API Reference						   SDL_AudioCVT(3)

NAME

       SDL_AudioCVT - Audio Conversion Structure

STRUCTURE DEFINITION

       typedef struct{
	 int needed;
	 Uint16 src_format;
	 Uint16 dest_format;
	 double rate_incr;
	 Uint8 *buf;
	 int len;
	 int len_cvt;
	 int len_mult;
	 double len_ratio;
	 void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
	 int filter_index;
       } SDL_AudioCVT;

STRUCTURE DATA

       needed		   Set to one if the conversion is possible

       src_format	   Audio format of the source

       dest_format	   Audio format of the destination

       rate_incr	   Rate conversion increment

       buf		   Audio buffer

       len		   Length of the original audio buffer in bytes

       len_cvt		   Length of converted audio buffer in bytes (calculated)

       len_mult 	   buf must be len*len_mult bytes in size(calculated)

       len_ratio	   Final audio size is len*len_ratio

       filters[10](..)	   Pointers to functions needed for this conversion

       filter_index	   Current conversion function

DESCRIPTION

       The  SDL_AudioCVT  is  used to convert audio data between different formats. A SDL_AudioCVT structure is created with the SDL_BuildAudioCVT
       function, while the actual conversion is done by the SDL_ConvertAudio function.

       Many of the fields in the SDL_AudioCVT structure should be considered private and their function will not be discussed here.

       Uint8 *buf

       int len

       int len_mult

       double len_ratio

SEE ALSO

       SDL_BuildAudioCVT, SDL_ConvertAudio, SDL_AudioSpec

SDL
							      Tue 11 Sep 2001, 22:58						   SDL_AudioCVT(3)

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