C Language, printf format string: how bad style is this?

printf format string: how bad style is this?

Author	Message
Stig Brautase #1 / 12	printf format string: how bad style is this? Hi, I've got a few functions (similar to f() in the program below), all containing calls to printf(). The functions themselves are different, but the printf() format string should be the same in all of them. Now, is it okay to just #define the format string as in the program below, or should I create a variable and pass this to the functions in question as an extra parameter? /* this program just prints garbage / #include <stdio.h> #define FORMAT "% 5.3f " void f(double arr, int len) { int i; for (i = 0; i < len; i++) { printf(FORMAT, arr[i]); } putchar('\n'); Quote: } int main(void) { double a[10]; f(a, 10); return 0; Quote: } Stig -- brautaset.org
Sat, 26 Mar 2005 23:29:01 GMT

Serve Laurijsse #2 / 12	printf format string: how bad style is this? Quote: > I've got a few functions (similar to f() in the program below), all > containing calls to printf(). The functions themselves are different, > but the printf() format string should be the same in all of them. Now, > is it okay to just #define the format string as in the program below, or > should I create a variable and pass this to the functions in question as > an extra parameter? That's a matter of opinion. I think it's fine with the macro
Sun, 27 Mar 2005 00:30:03 GMT

CBFalcone #3 / 12	printf format string: how bad style is this? Quote: > I've got a few functions (similar to f() in the program below), > all containing calls to printf(). The functions themselves are > different, but the printf() format string should be the same in > all of them. Now, is it okay to just #define the format string > as in the program below, or should I create a variable and pass > this to the functions in question as an extra parameter? > /* this program just prints garbage / > #include <stdio.h> > #define FORMAT "% 5.3f " > void f(double arr, int len) > { > int i; > for (i = 0; i < len; i++) { > printf(FORMAT, arr[i]); > } > putchar('\n'); > } > int main(void) > { > double a[10]; > f(a, 10); > return 0; > } Of course it does. The contents of a are uninitialized. -- Available for consulting/temporary embedded and systems. <http://cbfalconer.home.att.net> USE worldnet address!
Sun, 27 Mar 2005 00:45:23 GMT

nevr #4 / 12	printf format string: how bad style is this? i would just ditch the #define statement all together. Do you thin that FORMAT will ever change? If no, then ditch it. Maybe you have bigger plans FORMAT... I find that using too many #defines/consts can make your code MORE confusing. It may be obvious what you mean by FORMAT today, but what if dig this code a few months from now, years? What if somebody else takes over the project? - nevry. Quote: > Hi, > I've got a few functions (similar to f() in the program below), all > containing calls to printf(). The functions themselves are different, > but the printf() format string should be the same in all of them. Now, > is it okay to just #define the format string as in the program below, or > should I create a variable and pass this to the functions in question as > an extra parameter? > /* this program just prints garbage / > #include <stdio.h> > #define FORMAT "% 5.3f " > void f(double arr, int len) > { > int i; > for (i = 0; i < len; i++) { > printf(FORMAT, arr[i]); > } > putchar('\n'); > } > int main(void) > { > double a[10]; > f(a, 10); > return 0; > } > Stig > -- > brautaset.org
Sun, 27 Mar 2005 00:46:29 GMT

E. Gibbo #5 / 12	printf format string: how bad style is this? Quote: >i would just ditch the #define statement all together. Do you thin that >FORMAT will ever change? If no, then ditch it. Maybe you have bigger plans >FORMAT... I find that using too many #defines/consts can make your code MORE >confusing. It may be obvious what you mean by FORMAT today, but what if dig >this code a few months from now, years? What if somebody else takes over the >project? (BTW, please don't top-post.) Gotta disagree: this seems like a perfect place for a macro, to me. A number of functions, which all must have the same output format. What if you decide to change the format? Perhaps a different number of decimal places. Or perhaps "%+5.3f " instead of "% 5.3f". If you had this hard-coded all over the place, how likely is it that you might miss one (especially if you didn't write it originally, and someone just told you to go in and change the output format)? Placed in a shared .h file, the macro can also facilitate "symbiosis" between the producer of these strings, and a downstream consumer: the consumer can look at FORMAT to tell exactly what to expect and how to parse it, and when it changes, everything will stay in step. --Ben Quote: >- nevry. >> Hi, >> I've got a few functions (similar to f() in the program below), all >> containing calls to printf(). The functions themselves are different, >> but the printf() format string should be the same in all of them. Now, >> is it okay to just #define the format string as in the program below, or >> should I create a variable and pass this to the functions in question as >> an extra parameter? >> /* this program just prints garbage / >> #include <stdio.h> >> #define FORMAT "% 5.3f " >> void f(double arr, int len) >> { >> int i; >> for (i = 0; i < len; i++) { >> printf(FORMAT, arr[i]); >> } >> putchar('\n'); >> } >> int main(void) >> { >> double a[10]; >> f(a, 10); >> return 0; >> } >> Stig >> -- >> brautaset.org --
Sun, 27 Mar 2005 01:53:20 GMT

Bj?rn Augesta #6 / 12	printf format string: how bad style is this? Quote: > Hi, > I've got a few functions (similar to f() in the program below), all > containing calls to printf(). The functions themselves are different, > but the printf() format string should be the same in all of them. Now, > is it okay to just #define the format string as in the program below, or > should I create a variable and pass this to the functions in question as > an extra parameter? > /* this program just prints garbage / > #include <stdio.h> > #define FORMAT "% 5.3f " > void f(double arr, int len) > { > int i; > for (i = 0; i < len; i++) { > printf(FORMAT, arr[i]); > } > putchar('\n'); > } > int main(void) > { > double a[10]; > f(a, 10); > return 0; > } > Stig How about creating a new function, e.g. print_formatted() and use the format string in one place only? Something like static inline int print_formatted(double d) { return printf("%5.3f ", d); Quote: } Bj?rn
Sun, 27 Mar 2005 02:20:53 GMT

nevr #7 / 12	printf format string: how bad style is this? Quote: > >i would just ditch the #define statement all together. Do you thin that > >FORMAT will ever change? If no, then ditch it. Maybe you have bigger plans > >FORMAT... I find that using too many #defines/consts can make your code MORE > >confusing. It may be obvious what you mean by FORMAT today, but what if dig > >this code a few months from now, years? What if somebody else takes over the > >project? > (BTW, please don't top-post.) > Gotta disagree: this seems like a perfect place for a macro, to me. > A number of functions, which all must have the same output format. > What if you decide to change the format? Perhaps a different number > of decimal places. Or perhaps "%+5.3f " instead of "% 5.3f". If > you had this hard-coded all over the place, how likely is it that > you might miss one (especially if you didn't write it originally, > and someone just told you to go in and change the output format)? > Placed in a shared .h file, the macro can also facilitate "symbiosis" > between the producer of these strings, and a downstream consumer: > the consumer can look at FORMAT to tell exactly what to expect and > how to parse it, and when it changes, everything will stay in step. > --Ben > >- nevry. > >> Hi, > >> I've got a few functions (similar to f() in the program below), all > >> containing calls to printf(). The functions themselves are different, > >> but the printf() format string should be the same in all of them. Now, > >> is it okay to just #define the format string as in the program below, or > >> should I create a variable and pass this to the functions in question as > >> an extra parameter? > >> /* this program just prints garbage / > >> #include <stdio.h> > >> #define FORMAT "% 5.3f " > >> void f(double arr, int len) > >> { > >> int i; > >> for (i = 0; i < len; i++) { > >> printf(FORMAT, arr[i]); > >> } > >> putchar('\n'); > >> } > >> int main(void) > >> { > >> double a[10]; > >> f(a, 10); > >> return 0; > >> } > >> Stig > >> -- > >> brautaset.org > -- I don't think either of us has enough information make a judgement. If FORMAT is used more than once or twice, then it's probobly a good idea to use it(i somehow missed him/her saying that...). If not, then it's probobly a waste of coding. On the other hand, if your coding team really likes macros, then use them, whatever you fell most comfortable with. The big question here is; will FORMAT ever change? Hint: Be careful to document what your macros mean, and where they are or might be used--even if you are a one-(wo)man 'team'. - nevry.
Sun, 27 Mar 2005 05:28:41 GMT

Stig Brautase #8 / 12	printf format string: how bad style is this? Quote: >>i would just ditch the #define statement all together. Do you thin that >>FORMAT will ever change? If no, then ditch it. Maybe you have bigger plans >>FORMAT... I find that using too many #defines/consts can make your code MORE >>confusing. It may be obvious what you mean by FORMAT today, but what if dig >>this code a few months from now, years? What if somebody else takes over the >>project? > (BTW, please don't top-post.) > Gotta disagree: this seems like a perfect place for a macro, to me. > A number of functions, which all must have the same output format. > What if you decide to change the format? Perhaps a different number > of decimal places. Or perhaps "%+5.3f " instead of "% 5.3f". If > you had this hard-coded all over the place, how likely is it that > you might miss one (especially if you didn't write it originally, > and someone just told you to go in and change the output format)? > Placed in a shared .h file, the macro can also facilitate "symbiosis" > between the producer of these strings, and a downstream consumer: > the consumer can look at FORMAT to tell exactly what to expect and > how to parse it, and when it changes, everything will stay in step. That was my idea. I'm not quite sure how much precision I need just yet, but this way it's easy to just print low-precision numbers for easy overview while debugging, and turning the precision way up when in "production". The code is for a coursework at uni, so it'll most likely just be thrown away after hand-in, however I was just asking for the general case. Stig -- brautaset.org
Sun, 27 Mar 2005 05:47:31 GMT

Stig Brautase #9 / 12	printf format string: how bad style is this? Quote: >> >> I've got a few functions (similar to f() in the program below), >> >> all containing calls to printf(). The functions themselves are >> >> different, but the printf() format string should be the same in >> >> all of them. Now, is it okay to just #define the format string as >> >> in the program below, or should I create a variable and pass this >> >> to the functions in question as an extra parameter? >> >i would just ditch the #define statement all together. Do you thin >> >that FORMAT will ever change? If no, then ditch it. Maybe you have >> >bigger plans FORMAT... I find that using too many #defines/consts >> >can make your code MORE confusing. It may be obvious what you mean >> >by FORMAT today, but what if dig this code a few months from now, >> >years? What if somebody else takes over the project? >> (BTW, please don't top-post.) >> Gotta disagree: this seems like a perfect place for a macro, to me. >> A number of functions, which all must have the same output format. >> What if you decide to change the format? Perhaps a different number > I don't think either of us has enough information make a judgement. If > FORMAT is used more than once or twice, then it's probobly a good idea > to use it(i somehow missed him/her saying that...). FORMAT is used more than once, and is likely to change, yes. Oh, and I'm a 'he' :) Stig -- brautaset.org
Sun, 27 Mar 2005 05:52:38 GMT

Chris Dor #10 / 12	printf format string: how bad style is this? Quote: > Hi, > I've got a few functions (similar to f() in the program below), all > containing calls to printf(). The functions themselves are different, > but the printf() format string should be the same in all of them. Now, > is it okay to just #define the format string as in the program below, or > should I create a variable and pass this to the functions in question as > an extra parameter? > /* this program just prints garbage / > #include <stdio.h> > #define FORMAT "% 5.3f " > void f(double arr, int len) > { > int i; > for (i = 0; i < len; i++) { > printf(FORMAT, arr[i]); > } > putchar('\n'); > } > int main(void) > { > double a[10]; > f(a, 10); > return 0; > } I tend to do static const char FORMAT[] = "% 5.3f "; mainly because I suffered some early compilers which would create n copies of "% 5.3f ", even though you weren't modifying any of them [one even created a string for sizeof("% 5.3f ")!]. Sensible compilers know (or can be told) to create only one copy. Chris
Sun, 27 Mar 2005 07:36:00 GMT

Kevin Brace #11 / 12	printf format string: how bad style is this? Quote: > I tend to do > static const char FORMAT[] = "% 5.3f "; > mainly because I suffered some early compilers which would create n > copies of "% 5.3f ", even though you weren't modifying any of them > [one even created a string for sizeof("% 5.3f ")!]. Sensible compilers > know (or can be told) to create only one copy. I think you're probably on safe ground with string literals now :) C99's compound literals re-introduce the problem though. I'd be interested to know what other compilers' approaches have been. In my implementation void Draw(Point); Draw((Point) { 1, 2 }); Draw((Point) { 2, 3 }); Draw((Point) { 1, 2 }); would create 2 copies of (Point) { 1, 2 }, but Draw((const Point) { 1, 2 }); Draw((const Point) { 2, 3 }); Draw((const Point) { 1, 2 }); will only create 1 copy of (const Point) { 1, 2 }. Now a brighter compiler shouldn't need the const to avoid the duplicate literal, but I'm not sure how many, if any, are bright enough here. In this case, an even brighter compiler wouldn't allocate a Point object - it'd just pass the right values to the function directly, just like passing a scalar. (As an aside, your sizeof example just filled me with dread, but I've checked and I'm not actually creating a compound literal for that case. Phew.) -- Kevin Bracey http://www.bracey-griffith.freeserve.co.uk/
Sun, 27 Mar 2005 17:41:45 GMT

Dan P #12 / 12	printf format string: how bad style is this? Quote: >That was my idea. I'm not quite sure how much precision I need just yet, >but this way it's easy to just print low-precision numbers for easy >overview while debugging, and turning the precision way up when in >"production". The code is for a coursework at uni, so it'll most likely >just be thrown away after hand-in, however I was just asking for the >general case. If it's only the precision that it's likely to change, it's probably better to use a macro only for the precision, and use the * feature to specify the precision. This way, you can have the same precision everywhere (you need), even if the format strings are otherwise different. OTOH, if you need to have the identical format string everywhere and any part of it is subject to later changes, either use your approach or define a macro for the whole printf call. Dan -- Dan Pop DESY Zeuthen, RZ group
Sun, 27 Mar 2005 18:28:09 GMT

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