Thread: Looking to extract a hex value out of a buffer

I did received help on how to display a hex value.
I'm now looking for a way to extract a hex value out of a buffer.

Ex.

I have a buffer( 200 bytes long).
The first 38 bytes contains rt, account and serial number as readable numerics.

0012333990000000080002340000051751177
From this I'm able to manipulate via string copies ....

strncpy(&rt,buffer_input + 1,10);
strncpy(&account,buffer_input + 11,18); ..ect

Postions 39-46 is the amount field *******IN HEX *******.
00000050
0000000C

QUESTION 1.....how can I display the hex value from this buffer.
(can I use a strncpy + other manipulations)
strncpy(&hex,buffer_input + 39,8);

QUESTION 2 can I change this hex value to a "readable" numeric and write out to a file.

Thanks for any recommendations in advance.

MMC

Thanks Stoned_coder

But what I think I'm looking for is

Positions/bytes in my buffer
1234.............................................. .................38

0012333990000000080002340000051751177

39.........47

00000050
0000000C

How do I get pos 39 - 47 in its own buffer/field to display +
how do I turn it into a value that I can add to other numbers.

Any thoughts ??????

Assuming the data isn't ascii, you could do this:

int num;
num = *((int *) buffer_input+38);
printf("num:%X\n",num);
printf("num:%d\n",num);

Assuming an int is 4 bytes, this would take the next 4 bytes and store it in num.

If it's ascii, then you could to this:

int num;
char a[9];

strncpy(a,buffer_input+38,8);
*(a+8) = '\0';
num = atoi(a);
printf("num:%X\n",num);
printf("num:%d\n",num);

Thanks Swoopy !
I'll give that a try and post my results.

Swoopy, I tried and suggestions and I'm now able to display hex values............ at a certain positions.

BUT....I still not able to set my position correctly.

Ex.
int num;
num = *((int *) buffer_input+38); ....goes to position 133 not 39.
printf("num:%X\n",num);
printf("num:%d\n",num);

Results
This actually get 4 bytes at position 133.
4(I guess because I specify int) x 38 + 1 = 133

Other tests

num = *((int *) buffer_input);
Postion 1
buffer_input +1 = position 5
buffer_input + 2 = position 9 ....

I'm looking to start my 4 bytes at position 39.....any thoughts on how to set my pointer

if I do buffer_input + 9 = position 37......just now sure how to get to position 39.

Any thoughts....again thanks for your patience and help.

MMC,
How is buffer_input declared? Is it:
char *buffer_input;

If yes, then this should do the trick:
num = *((int *) (buffer_input+38));

This will move the pointer 38 as a character pointer, before casting to an integer pointer.
As you have pointed out, as an integer pointer, it moves it 38*4.

I'm able to use
num = *((char*) buffer_input+44);
printf("num:%X\n",num);
printf("num:%d\n",num);

I used char instead of int ...
This gives me the hex and integer value for a position.

Is this my only option ?

Anyway, thanks to all....I feel I'm making progress !!!

MMC

Thanks Everyone !!!