0

I have data stored in text_buf[4] = {0x1d, 0x72, 0x2f, 0x32}.When I send it to display on LCD, it displays some garbage. I understand that LCD displays only string, how do I make it to display hex values that is stored in text_buf? Are there any C examples for this? Please do let me know.

Grijesh Chauhan
  • 57,103
  • 20
  • 141
  • 208
user2874122
  • 3
  • 2
  • 1
    Possible duplicate? http://stackoverflow.com/questions/3649026/how-to-display-hexadecimal-numbers-in-c – Rivasa Oct 12 '13 at 13:57
  • 1
    do you have any code? what is the desired output? if your LCD prints only strings - convert the buffer to a string and print it – jev Oct 12 '13 at 14:02

2 Answers2

6

Use snprintf() family to format your text_buf (or any data) to a char array and call your LCD's display routine.

char line[256];
snprintf(line, sizeof(line), "%02x %02x %02x %02x\n", text_buf[0], text_buf[1], text_buf[2], text_buf[3]);
LCD_print(line); // LCD's display routine

Reference for format sequence.

leesei
  • 6,020
  • 2
  • 29
  • 51
  • 3
    You "misspelled" `snprintf()`. Also, no cplusplus.com, please. Firstly because it's bad, secondly because this is a C question. –  Oct 12 '13 at 14:15
  • Ha, I'll "correct the spelling" then. But that reference is to the C library and so I think it is suitable. – leesei Oct 12 '13 at 14:18
  • 2
    unfortunately, that's not the case. I suggest you take a look at [a true C reference](http://pubs.opengroup.org/onlinepubs/7908799/xsh/sprintf.html). –  Oct 12 '13 at 14:19
  • @H2CO3: technically, that's a POSIX reference. – Matteo Italia Oct 12 '13 at 14:24
  • @MatteoItalia It is. But at least it's official and it doesn't suffer from hundreds of fundamental errors. And it's about C, not C++. –  Oct 12 '13 at 14:25
  • I intended to provide an easy reference of formatting sequence to the OP (who seems to be new to C). The official things are not user friendly IMHO. – leesei Oct 12 '13 at 14:28
  • 1
    Using C++ documentation for the C stdlib is not `programmer friendly` , nor is it `computer friendly` . – wildplasser Oct 12 '13 at 14:30
  • @leesei Why do you think that a C++ reference is more "user friendly" than a C one? (Also, as I just stated, it's wrong. Would you rather supply your user with a wrong but "friendly" reference than a correct but more technical one? I hope not.) –  Oct 12 '13 at 14:32
  • @MatteoItalia Check out my updated answer, hope it's better now... –  Oct 12 '13 at 14:32
  • Do not take this as a challenge, but I genuinely are not aware of the difference of the `printf()` API/implementation difference in C and C++. I only meant the tabulated layout and examples are more user friendly for a learner. – leesei Oct 12 '13 at 14:35
  • @leesei No problem. There's no difference (well, there should be no difference...) between `printf()` in `` and `printf()` in ``. It's only that one should not contribute to the common misconception that "C is a subset of C++", since it isn't. I (and apparently others too) felt that you kind of supported this by treating C and C++ things as if they were interchangeable. I see that you wanted to do something good :) This is just a piece of advice. –  Oct 12 '13 at 14:38
  • @H2CO3 K, but C tutorial are indeed hard for beginners (they are all ASCII text ;-p). Do you guys have any recommendations beyond SUS? – leesei Oct 12 '13 at 14:42
  • @leesei, for learning C? K&R's 2nd Ed. is a good book as well Kochan's `Programming in C` – Rivasa Oct 12 '13 at 14:44
  • Any other online reference? (I'll keep SUS in my bookmark from now on.) – leesei Oct 12 '13 at 14:45
3

Be safe and use snprintf(). Also add a loop to generalize the task and to decrease redundancy:

char text[0x1000]; // or however many
size_t n = 0;
for (size_t i = 0; i < sizeof(buf) / sizeof(buf[0]); i++) {
    int delta = snprintf(text + n, sizeof(text) - n, "%02x ", buf[i]);
    if (delta < 0)
        break; // handle error!

    n += delta;
}

(documentation)

Technically, the documentation above concerns POSIX, not only standard C. So in case anyone wonders: section 7.19.6.5 of the C99 Standard (I couldn't find the C11 one online) concerns this very function. Clause 7.19.6.1.8 describes the conversion specifiers.

  • 2
    I originally down voted this answer because it is overly complex in my opinion. H2C03 and I had a long "discussion" and in the end he pointed out to me that down votes are for technically incorrect answers or spam. I am removing my down vote because his answer is not incorrect nor spam.. – Charlie Burns Oct 12 '13 at 15:17