Post by thread:[PICLIST] String constants in ANSI C

A couple of quick C questions - I'm actually using an ST7 compiler but I would expect this stuff to be 'ansi standard' - I can't find the answer in the couple of rather poor C books I have. How do you concatenate parts of a string constant into a single string at compile time? For example, what I want to do is something like : #define clschar 0x01 #define tabchar 0x02 disp(clschar+tabchar); Obviously the compiler complains about this! I can of course do disp("\x01\x02"); but that defeats the point of trying to use meaningful names for control characters. How do I tell the compiler that I want a 2-character string "\x01\x02" and not a single character 03 ? Another problem I've found is when mixing ascii and escape characters, e.g. disp("\x01Code"); the 'C' appears to be interpreted as part of the escape sequence, not a new character. other than turning ascii 0-9,A-F into hex is there a way round this ? I'm not sure if this one is a compiler problem or a problem with the Ansi spec - there's no reason it would need to look at more than 2 characters in the escape sequence. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:"

A couple of quick C questions - I'm actually using an ST7 compiler but I would expect this stuff to be 'ansi standard' - I can't find the answer in the couple of rather poor C books I have. How do you concatenate parts of a string constant into a single string at compile time? For example, what I want to do is something like : #define clschar 0x01 #define tabchar 0x02 disp(clschar+tabchar); Obviously the compiler complains about this! I can of course do disp("\x01\x02"); but that defeats the point of trying to use meaningful names for control characters. Use the preprocessor concatenation operator, ##. For ex: #define past(front, back) front ## back From the venerable K&R: "The preprocessor operator ## provides a way to concatenate actual arguments during macro expansion. If a parameter in the replacement text is adjacent to a ##, the parameter is replaced by the actual argument, the ## and surrounding white space are removed, and the result is re-scanned."(c) Second Edition, pg. 90. -d (c) Prentice-Hall, Inc. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads

C concats adjacent strings: disp("\x01" "Code"); == Rich On Tue, 24 Oct 2000, Mike Harrison wrote: {Quote hidden}> Date: Tue, 24 Oct 2000 15:00:28 +0100 > From: Mike Harrison <spam_OUTmikeTakeThisOuTwhitewing.co.uk> > To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Subject: String constants in ANSI C > > > A couple of quick C questions - I'm actually using an ST7 compiler but > I would expect this stuff to be 'ansi standard' - I can't find the > answer in the couple of rather poor C books I have. > > How do you concatenate parts of a string constant into a single string > at compile time? > > For example, what I want to do is something like : > #define clschar 0x01 > #define tabchar 0x02 > > disp(clschar+tabchar); > > Obviously the compiler complains about this! > I can of course do disp("\x01\x02"); but that defeats the point of > trying to use meaningful names for control characters. > > How do I tell the compiler that I want a 2-character string "\x01\x02" > and not a single character 03 ? > > Another problem I've found is when mixing ascii and escape characters, > e.g. > disp("\x01Code"); > the 'C' appears to be interpreted as part of the escape sequence, not > a new character. other than turning ascii 0-9,A-F into hex is there a > way round this ? > I'm not sure if this one is a compiler problem or a problem with the > Ansi spec - there's no reason it would need to look at more than 2 > characters in the escape sequence. > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > "[PIC]:","[SX]:","[AVR]:" ÿ ONLY! "[EE]:","[OT]:" ÿher "[BUY]:","[AD]:" s > > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:"

> How do you concatenate parts of a string constant into a single string > at compile time? > > For example, what I want to do is something like : > #define clschar 0x01 > #define tabchar 0x02 > > disp(clschar+tabchar); > > Obviously the compiler complains about this! > I can of course do disp("\x01\x02"); but that defeats the point of > trying to use meaningful names for control characters. static const char mystring[] = {clschar, tabchr, 't', 'e', 's', 't', 0}; disp(mystring); BillW -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads

Concatenating strings and concatenating characters are two different things. You have two characters #defined. To concatenate them you must first make them strings. Of course there are shortcuts. Since strings are arrays of char in C, you can so this: char buffer[8]; buffer[0]=CHAR1; buffer[1]=CHAR2; buffer[2]='\0'; /* this assignment is part of that proverbial rope */ disp(buffer); Or: sprintf(buffer,"%c%c",CHAR1,CHAR2); disp(buffer); which does exactly the same thing but is more flexible. If you already use a printf statement in your code then you can use the second form. If you have no other printf then the first form will (may) save program space. hope this helps, Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

In-Reply-To: <00ed01c03dc6$34630f20$810000c0@dkott> David Kott <dkottKILLspamtestprod.com> wrote: > Use the preprocessor concatenation operator, ##. You are answering the wrong question. Brian Gregory. .....briangKILLspam.....cix.co.uk -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

----- Original Message ----- From: Peter L. Peres <EraseMEplpspam_OUTTakeThisOuTACTCOM.CO.IL> To: <PICLISTspam_OUTMITVMA.MIT.EDU> Sent: Thursday, October 26, 2000 2:33 PM Subject: Re: [OT]: String constants in ANSI C (Was : String constants in ANSI C) {Quote hidden}> Concatenating strings and concatenating characters are two different > things. You have two characters #defined. To concatenate them you must > first make them strings. Of course there are shortcuts. Since strings are > arrays of char in C, you can so this: > > char buffer[8]; > > buffer[0]=CHAR1; > buffer[1]=CHAR2; > buffer[2]='\0'; /* this assignment is part of that proverbial rope */ > > disp(buffer); > > Or: > > sprintf(buffer,"%c%c",CHAR1,CHAR2); > disp(buffer); > > which does exactly the same thing but is more flexible. If you already use > a printf statement in your code then you can use the second form. If you > have no other printf then the first form will (may) save program space. Unfortunately, sprintf uses most of the same code as printf, so it won't reduce program size to use sprintf. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) {Quote hidden}> > hope this helps, > > Peter > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> #define clschar "\x01" > #define tabchar "\x02" > disp(clschar tabchar); > > If I remember correctly, the preprocessor will boil it down to this: > disp( "\x01" "\x02" ); > which should give you what you want. Ahh. Forgot about that one. I don't thing compiler string concatenation ("ab" "cd" --> "abcd") is standardized, but some compilers do this, and I like this much better than my initialized string example! Watch out for accidentally adding the comma, cause that'll be quite different! BillW -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>Unfortunately, sprintf uses most of the same code as printf, so it won't >reduce program size to use sprintf. What I was trying to say was, that if you already use printf or sprintf in your program, then go ahead and use it here too, else avoid it. I am sorry if I did not make myself clear. Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

----- Original Message ----- From: Douglas Wood <@spam@douglas_woodKILLspamARIUSA.COM> To: <KILLspamPICLISTKILLspamMITVMA.MIT.EDU> Sent: Thursday, October 26, 2000 11:29 AM Subject: Re: [OT]: String constants in ANSI C (Was : String constants in ANSI C) > Actually, all of the xprintf functions use the core routines of sprintf to > create the formatted output string before sedning that data to the target > output (console for printf, files for fprintf, etc.) Actually, it depends on the C library, but most of them have a core function whose prototype might look something like this: void __anyprintf( void f(char), void *ctx, char const *, va_args *ap); ie: this is a function that takes an arbitrary function 'f' and context 'ctx' and feeds it the characters resulting from formatting the data. now fprintf, printf, sprintf just call __anyprintf with an appropriate function to dispose of the characters properly. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I forgot to mention that it is VERY wasteful to define short STRINGS. This is because of the terminating '\0' which consumes at least one extra location per string. For example, five one-character constant strings consume 10 program locations for definition, and at least one more for each invocation in the code (to load the pointer, for a total of at least 15 !, whereas five #defined one character constants consume one location each in program space, for every time they are invoked, and no constant storage at all. In other words, the code consumption for #defined one character constants is at least 3 times lower than for #defined or constant strings. Similar logic applies for two character strings. The break even happens at three character strings with 12 and 14 bit PICs I think. These ideas are valid for any architecture (but with different break even sizes). Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> Actually, it depends on the C library, but most of them have a core function > whose prototype might look something like this: > > void __anyprintf( void f(char), void *ctx, char const *, va_args *ap); And man, many's the time I wished it was standard. Great for streaming formatted text to somewhere w/o need of intermediate buffer, but unfortunately a dangerous hack. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.