Printing char buffer in hex array

Question

I am reading 512 chars into a buffer and would like to display them in hex. I tried the following approach, but it just outputs the same value all the time, despite different values should be received over the network.

char buffer[512];
bzero(buffer, 512);
n = read(connection_fd,buffer,511);
if (n < 0) printf("ERROR reading from socket");
printf("Here is the message(%d): %x\n\n", sizeof(buffer), buffer);

Is it possible that here I am outputting the address of the buffer array, rather than its content? Is there an easy way in C for this task or do I need to write my own subroutine?

possible duplicate of [Printing the hexadecimal representation of a char array\[\]](http://stackoverflow.com/questions/10375932/printing-the-hexadecimal-representation-of-a-char-array) — Ciro Santilli OurBigBook.com, Jun 27 '15 at 21:58

Mark Stevens · Accepted Answer · 2012-11-07T17:55:19.343

19

This will read the same 512 byte buffer, but convert each character to hex on output:

char buffer[512];
bzero(buffer, 512);
n = read(connection_fd,buffer,511);
if (n < 0) printf("ERROR reading from socket");

printf("Here is the message:n\n");
for (int i = 0; i < n; i++)
{
    printf("%02X", buffer[i]);
}

edited Nov 07 '12 at 17:55

answered Nov 07 '12 at 17:50

Mark Stevens

2,366
14
9

3

You probably want `"%02X"` instead of `"%X"`, since otherwise single-digit values (that is bytes in the range 0-15 decimal) will print as a single digit. – danfuzz Nov 07 '12 at 17:54
Great, that works. Thanks guys for all the comments, really helpful to get back into basic C stuff :). – Patrick Nov 08 '12 at 09:52
you want *(unsigned char)* – Antti Haapala -- Слава Україні Sep 28 '17 at 10:14

score 2 · Answer 2 · answered Nov 07 '12 at 17:55

To display a char in hex you just need the correct format specificer and you need to loop through your buffer:

//where n is bytes back from the read:
printf("Here is the message(size %d): ", n);
for(int i = 0; i<n; i++)
     printf("%x", buffer[i]);

The code you were using was printing the address of the buffer which is why it wasn't changing for you.

Since it's been a while for you, if you'd like to see each byte nicely formatted 0xNN you can also use the %#x format:

for(int i = 0; i<n; i++)
    printf("%#x ", buffer[i]);

To get something like:

0x10 0x4 0x44 0x52...

It's a shame that `%#x` only prepends `0x` if not 0. – Gauthier Jan 23 '20 at 13:49 — Gauthier, Jan 23 '20 at 13:49

score -1 · Answer 3 · answered Nov 07 '12 at 17:51

-1

This isn't how C works at all. If anything, you are printing the address of the buffer array.

You will need to write a subroutine that loops through each byte in the buffer and prints it to hexadecimal.

And I would recommend you start accepting some answers if you really want people to help you.

answered Nov 07 '12 at 17:51

Jonathan Wood

65,341
71
269
466

3

Hmm, never go on SO without that morning cup of coffee. – bryc Feb 17 '19 at 19:01

Printing char buffer in hex array

3 Answers3

Linked