how to use hex escape char with string in C?

Applications Programming
1

I want it to ouput "abcd", but it dosen't.

  1 #include<stdio.h>
  2 int main()
  3 {
  4         printf("a\x62cd");
  5 }
  6

gcc alarm.c -o alarm
alarm.c: In function 'main':
alarm.c:4:9: warning: hex escape sequence out of range

It seems that the complier joint "cd" as part of \x62.
Maybe I can write it like this:

printf("a\x62""cd");

but it is a bit urgly...

2

That's what I ended up having to do before. That, or seperating it out of the string entirely as in printf("a%ccd", 0x62);

3

Why don't the complier just translates the fixed few of characters(eg: two char) after \x to an escape char?

4

Why should it? There are systems where "char" isn't 8 bits... Or were, decades ago, and the C standard people latch onto this technicality like a bear trap and refuse to let go.

It plainly doesn't assume it stops at 8 bits, anyway, so the question's kind of pointless.

5

Unicode characters aren't 8 bits, and they've been spotted in use somewhat more recently than decades ago.

The only way to produce a deterministic result when the number of output bits can not be constrained is with a maximal-munch parser.

6

I tried your code with the same result as you. Then I just tried the following code:

  1 #include<stdio.h>
  2 int main()
  3 {
  4         printf("a\x62mn");
  5 }
  6

with the output:

#rob@fred:~/programs$./unixcom.exee
abmn
rob@fred:~/programs$

I think what is happening with your code is that the compiler is reading the \x62cd as one hex number - \xbcd. I would guess that Corona688's suggestion - printf("a%ccd", 0x62) - is your best bet.

HTH,

Rob.

7

achenle - unicode or utf-16 or whatever else - have been around for a long time. They are not considered 'char' in C, they are wchar, wide characters, a different datatype. This datatype affects file orientation, which is the primary way reads & writes occur on tyy/file/device(s). wchar are NOT char, by definition and practice

try man wchar

And there still are embedded systems with 32 bit char.

8

And string literals aren't char datatypes, either. They're string literals.

If you're going to be annoyingly pedantic at least be correct.

9

"Annoyingly pedantic" is a decent description of a few corner cases in C like this. Assumptions people make about their machine (char == 8 bits) don't square perfectly with C's model of it.