How to read first four bytes from a file

[techie929]

Hi,

I need to read 4 bytes from file to form a 32-bit unsigned integer X. The first byte you read goes into the most-significant byte of X, the 2nd byte you read goes into the 2nd most-significant byte of X, the 3rd byte you read goes into the 3rd most-significant byte of X, and the 4th byte you read goes into the least-significant byte of X.

Here is the content of the file:

000000: 29 52 61 96 e1 bd 74 f9 1c d1 3c d6 6a 61 64 71 )Ra~~~t~.~<~jadq
000010: f8 41 8f 8d 55 de a1 b0 6a 21 8d 98 54 62 94 83 ~A~~U~~~j!~~Tb~~
000020: 6c 1b f4 5f 33 84 f2 e7 88 57 ce 98 31 29 08 5d l.~_3~~~~W~~1).]
000030: dd 14 25 82 52 c2 46 95 19 df f6 46 ae bf 54 d0 ~.%~R~F~.~~F~~T~
000040: c6 9a 47 79 5f 61 a4 3b e1 35 59 64 6f 08 67 1e ~~Gy_a~;~5Ydo.g.
000050: a9 9c 9a 05 dd a1 82 74 fc 66 16 38 c6 d7 0d 46 ~~~.~~~t~f.8~~.F
000060: 32 56 4b 3a d3 bf c7 da 2b 99 90 7c 8d cc eb b4 2VK:~~~~+~~|~~~~
000070: df bc 58 4b 12 62 c6 77 8d df 3b b0 f0 e1 5c 12 ~~XK.b~w~~;~~~\.
000080: 2d 53 ee 63 40 28 01 28 5a 48 6d 24 56 69 dc f2 -S~c@(.(ZHm$Vi~~
000090: ae 61 54 2e 65 8d b0 54 05 09 4a c2 2d 8f 9f d0 ~aT.e~~T..J~-~~~
0000a0: d6 09 12 3e e8 6a 45 0c c6 ac b6 8d 52 c8 1d 32 ~..>~jE.~~~~R~.2
0000b0: 59 81 51 7a e3 c9 7d df ab 03 28 6e 4a 2a 16 62 Y~Qz~~}~~.(nJ*.b
0000c0: b5 f6 a1 e7 79 99 70 b9 fe f0 28 c7 34 62 bd 10 ~~~~y~p~~~(~4b~.
0000d0: 70 dc d2 e8 8c 80 9a cc 6d 84 13 09 a7 0b ef 52 p~~~~~~~m~..~.~R
0000e0: 59 5b 97 0c 3d c2 aa ba da 11 89 5a 35 60 e4 74 Y[~.=~~~~.~Z5`~t
0000f0: a1 3d 28 34 81 63 2c d2 97 06 43 d1 cc b5 32 95 ~=(4~c,~~.C~~~2~
000100: b2 48 8e 4b 3c 10 7a d3 7b 09 fa bc b7 d9 2d c2 ~H~K<.z~{.~~~~-~
000110: 29 a8 90 b2 39 77 ec 3e f5 bd d4 52 dc 8c 8b 70 )~~~9w~>~~~R~~~p
000120: af f9 9f dd f4 ec 20 96 97 6a 47 2c bb c7 a4 32 ~~~~~~ ~~jG,~~~2
000130: 55 12 d9 05 d6 82 ed 6e 49 77 a6 42 b3 f0 08 b9 U.~.~~~nIw~B~~.~
000140: 2b 1d e3 71 6b 8d 74 29 88 1d c5 1b e9 50 26 0f +.~qk~t)~.~.~P&.
000150: 35 59 c6 b6 19 17 fe 8e a7 ba d6 2e 7a 21 d3 e3 5Y~~..~~~~~.z!~~
000160: 1c 70 ef 6a 2d a3 4f 6e fe 25 4a e1 38 67 85 ef .p~j-~On~%J~8g~~
000170: d6 a6 c7 bb ca e1 07 07 48 a0 24 a2 4f 90 08 39 ~~~~~~..H~$~O~.9
000180: f3 11 22 2b ed a0 50 3f 87 57 49 02 be 86 6f d9 ~."+~~P?~WI.~~o~
000190: c7 92 b6 eb 26 0a c4 b8 30 b6 08 f1 4b 02 43 ed ~~~~&.~~0~.~K.C~
0001a0: 2f 4b cb 0f 5e 1d a3 08 56 5f f7 54 db 40 6b 3d /K~.^.~.V_~T~@k=

Could anyone tell me how to do this???

[techie929]

Hi,

I need to read 4 bytes from file to form a 32-bit unsigned integer X. The first byte you read goes into the most-significant byte of X, the 2nd byte you read goes into the 2nd most-significant byte of X, the 3rd byte you read goes into the 3rd most-significant byte of X, and the 4th byte you read goes into the least-significant byte of X.

Here is the content of the file:

000000: 29 52 61 96 e1 bd 74 f9 1c d1 3c d6 6a 61 64 71 )Ra~~~t~.~<~jadq
000010: f8 41 8f 8d 55 de a1 b0 6a 21 8d 98 54 62 94 83 ~A~~U~~~j!~~Tb~~
000020: 6c 1b f4 5f 33 84 f2 e7 88 57 ce 98 31 29 08 5d l.~_3~~~~W~~1).]
000030: dd 14 25 82 52 c2 46 95 19 df f6 46 ae bf 54 d0 ~.%~R~F~.~~F~~T~
000040: c6 9a 47 79 5f 61 a4 3b e1 35 59 64 6f 08 67 1e ~~Gy_a~;~5Ydo.g.
000050: a9 9c 9a 05 dd a1 82 74 fc 66 16 38 c6 d7 0d 46 ~~~.~~~t~f.8~~.F
000060: 32 56 4b 3a d3 bf c7 da 2b 99 90 7c 8d cc eb b4 2VK:~~~~+~~|~~~~
000070: df bc 58 4b 12 62 c6 77 8d df 3b b0 f0 e1 5c 12 ~~XK.b~w~~;~~~\.
000080: 2d 53 ee 63 40 28 01 28 5a 48 6d 24 56 69 dc f2 -S~c@(.(ZHm$Vi~~
000090: ae 61 54 2e 65 8d b0 54 05 09 4a c2 2d 8f 9f d0 ~aT.e~~T..J~-~~~
0000a0: d6 09 12 3e e8 6a 45 0c c6 ac b6 8d 52 c8 1d 32 ~..>~jE.~~~~R~.2
0000b0: 59 81 51 7a e3 c9 7d df ab 03 28 6e 4a 2a 16 62 Y~Qz~~}~~.(nJ*.b
0000c0: b5 f6 a1 e7 79 99 70 b9 fe f0 28 c7 34 62 bd 10 ~~~~y~p~~~(~4b~.
0000d0: 70 dc d2 e8 8c 80 9a cc 6d 84 13 09 a7 0b ef 52 p~~~~~~~m~..~.~R
0000e0: 59 5b 97 0c 3d c2 aa ba da 11 89 5a 35 60 e4 74 Y[~.=~~~~.~Z5`~t
0000f0: a1 3d 28 34 81 63 2c d2 97 06 43 d1 cc b5 32 95 ~=(4~c,~~.C~~~2~
000100: b2 48 8e 4b 3c 10 7a d3 7b 09 fa bc b7 d9 2d c2 ~H~K<.z~{.~~~~-~
000110: 29 a8 90 b2 39 77 ec 3e f5 bd d4 52 dc 8c 8b 70 )~~~9w~>~~~R~~~p
000120: af f9 9f dd f4 ec 20 96 97 6a 47 2c bb c7 a4 32 ~~~~~~ ~~jG,~~~2
000130: 55 12 d9 05 d6 82 ed 6e 49 77 a6 42 b3 f0 08 b9 U.~.~~~nIw~B~~.~
000140: 2b 1d e3 71 6b 8d 74 29 88 1d c5 1b e9 50 26 0f +.~qk~t)~.~.~P&.
000150: 35 59 c6 b6 19 17 fe 8e a7 ba d6 2e 7a 21 d3 e3 5Y~~..~~~~~.z!~~
000160: 1c 70 ef 6a 2d a3 4f 6e fe 25 4a e1 38 67 85 ef .p~j-~On~%J~8g~~
000170: d6 a6 c7 bb ca e1 07 07 48 a0 24 a2 4f 90 08 39 ~~~~~~..H~$~O~.9
000180: f3 11 22 2b ed a0 50 3f 87 57 49 02 be 86 6f d9 ~."+~~P?~WI.~~o~
000190: c7 92 b6 eb 26 0a c4 b8 30 b6 08 f1 4b 02 43 ed ~~~~&.~~0~.~K.C~
0001a0: 2f 4b cb 0f 5e 1d a3 08 56 5f f7 54 db 40 6b 3d /K~.^.~.V_~T~@k=

Could anyone tell me how to do this???

//The value of the first four bytes would be:

byte0=0x29,byte1=0x52 ,byte2= 0x61 ,byte3=0x96

[WaltP]

What have you tried? What did it give you?

[techie929]

I just know that the values of byte0,byte1,byte2 and byte3..
But please explain me how to fetch these values??

[abhimanipal]

First step will be to read from a file. You can use fread for that.
http://irc.essex.ac.uk/www.iota-six.co.uk/c/i2_feof_fgets_fread.asp

Now the 4 bytes that you want to read will be in a character array.
The next part is to assign these bytes to form a 4 byte unsigned number. This code will get you started.... But you will have to modify it to fulfill your specification.

int main()
{
        int y=0;
        char* ip;
        ip=(char*)&y;

        *ip=10;
        *(ip+1)=11;
        *(ip+2)=12;             //We are accessing individual bytes of a 
                                        // 4 byte integer
        *(ip+3)=13;
        printf("%u %u %u %u\n",(ip),(ip+1),(ip+2),(ip+3));
        
         printf("%x\n",y);

        return 0;
}

[WaltP]

I just know that the values of byte0,byte1,byte2 and byte3..
But please explain me how to fetch these values??

What have you tried? What did it give you?

[techie929]

Thanks for the reply.
Could you please explain why have you assigned 10,11,12 and 13 to ip??

What I am doing is:

unsigned int X=0;
 FILE *fp ;
         fp = fopen("rndfile.bin","r");

         if( fp == NULL )
         {
               puts ( "cannot open file" ) ;
               exit(1) ;
         }
	fread(&X, 4, 1, fp);

[WaltP]

For the 3rd f'ing time, WHAT DID IT GIVE YOU????

And look up the fopen() function for the proper use of the 2nd parameter.