how to use hex escape char with string in C?


 
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# 1  
Old 11-27-2010
how to use hex escape char with string in C?

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

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

but it is a bit urgly...

Last edited by vistastar; 11-27-2010 at 02:28 AM..
# 2  
Old 11-27-2010
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  
Old 11-27-2010
Why don't the complier just translates the fixed few of characters(eg: two char) after \x to an escape char?
# 4  
Old 11-29-2010
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  
Old 11-29-2010
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  
Old 11-30-2010
I tried your code with the same result as you. Then I just tried the following code:

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

with the output:
Code:
#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  
Old 11-30-2010
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.
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