jmsellens@watdragon.UUCP (12/05/86)
There seems to have been a long and somewhat futile discussion about
a macro to give control characters. Some say use "CTRL(X)", some
say "CTRL('X')". Here's a wonderful way, that is guaranteed to
be portable, easy to type, and easy to understand.
Make a file called ctrl.h with lines like
#define CTRLA '\001'
in it (should take mere seconds). Put #include "ctrl.h" in your
C source files and use CTRLA. No fuss, no muss. Easy to understand.
Portable. And it even works.paul@devon.UUCP (Paul Sutcliffe Jr.) (12/07/86)
In article <1955@watdragon.UUCP>, jmsellens@watdragon.UUCP (John M. Sellens) writes: > Make a file called ctrl.h with lines like > #define CTRLA '\001' > in it (should take mere seconds). Put #include "ctrl.h" in your > C source files and use CTRLA. No fuss, no muss. Easy to understand. > Portable. And it even works. That's fine if you know ahead of time what control characters you want to play with. However, if I want to find the ``control'' value of a variable, as in: foo() { char c, cc; ... cc = CTRL(c); ... } then your method, although good for what it was intended, won't do. -Paul -- Paul Sutcliffe, Jr. UUCP: {seismo,ihnp4,allegra,rutgers}!cbmvax!devon!paul Devon Computer Services COMPUSERVE: 76176,502 Allentown, Penna. Sarek: "Any message for your mother, Spock?" +1 215 398 3776 Spock: "Yes. Tell her 'I feel fine.'"
marcus@ihlpl.UUCP (Hall) (12/15/86)
In article <184@devon.UUCP> paul@devon.UUCP (Paul Sutcliffe Jr.) writes: >In article <1955@watdragon.UUCP>, jmsellens@watdragon.UUCP (John M. Sellens) writes: >> Make a file called ctrl.h with lines like >> #define CTRLA '\001' >> in it (should take mere seconds). Put #include "ctrl.h" in your >> C source files and use CTRLA. No fuss, no muss. Easy to understand. >> Portable. And it even works. > >That's fine if you know ahead of time what control characters you >want to play with. However, if I want to find the ``control'' value >of a variable, as in: > ..[example].. >then your method, although good for what it was intended, won't do. But then, neither did the initial definition for CTRL(X) that started this whole mess. Recall the initial definition: #define CTRL(X) ('X' ^ 0100) or something very similar that works only for the Reiser cpp (& similar). John Sellens' idea for cntrl.h leads to yet another possibility that maybe would implement CTRL for either cpp (Reiser or ANSI) in a way that would be compatible with the original definition (i.e. no 's required). Suppose that you have a file ctrl.h that contains: #define __CTRLA '\001' #define __CTRLB '\002' ... #define __CTRLZ '\003' #define CTRL(X) __CTRL/**/X /* Reiser cpp */ #define CTRL(X) __CTRL//**/**/X /* (May need to be this, to preserve X */ #define CTRL(X) __CTRL # X /* ANSI cpp */ This would still have some problems with things like CTRL(@) and CTRL(?), but it comes close.. Marcus Hall ..!ihnp4!ihlpl!marcus
arnold@emory.UUCP (12/23/86)
I hope somebody hasn't beat me to this. The whole fuss about
#define CTRL(X) ('X' & 037) /* ascii! */
in the Reiser cpp not being doable in ANSI C can be answered this way:
#define CTRL(X) (' ## X ## ' & 037) /* ascii only */
which uses the token concatenation operator to produce the character
constant. This should also work for things like
esc = CTRL([);
I am sure someone will correct me if I am wrong. Now, we can hopefully put
this to rest!
( Personally, I think CTRL(X) is bad style;
#define ctrl(x) ((x) & 037)
and using ctrl('x') makes the most sense to me. It is legal in both K&R C and
ANSI C, and allows using the macro on a char or int variable, not just on
a constant. So there. :-)
--
Arnold Robbins
CSNET: arnold@emory BITNET: arnold@emoryu1
ARPA: arnold%emory.csnet@csnet-relay.arpa
UUCP: { akgua, decvax, gatech, sb1, sb6, sunatl }!emory!arnoldmeissner@dg_rtp.UUCP (Michael Meissner) (12/31/86)
In article <1971@emory.UUCP> arnold@emory.UUCP (Arnold D. Robbins {EUCC}) writes: > I hope somebody hasn't beat me to this. The whole fuss about > > #define CTRL(X) ('X' & 037) /* ascii! */ > > in the Reiser cpp not being doable in ANSI C can be answered this way: > > #define CTRL(X) (' ## X ## ' & 037) /* ascii only */ > > which uses the token concatenation operator to produce the character > constant. .... This will not work with the ANSI preprocessor, because the ANSI preprocessor only deals with tokens, not atoms (except for string-izing). The above would try to create a character constant with 8 characters in it. -- Michael Meissner, Data General ...mcnc!rti-sel!dg_rtp!meissner