# Numeric constants as strings 11 messages from 2007-02-19 to 2007-02-20. Participants: Andy Parkins, Junio C Hamano, Shawn O. Pearce, Matthieu Moy, Mark Wooding, Jakub Narebski. Thread: https://gitlist.dev/t/6879 ## Andy Parkins, 2007-02-19 09:16 Subject: Numeric constants as strings Message-ID: <200702190916.35813.andyparkins@gmail.com> URL: https://gitlist.dev/e/200702190916.35813.andyparkins%40gmail.com ``` Hello, I'm working on bringing my hash width literals patch up to date now that 1.5.0 has passed. It's all been trivial apart from one line: #define HASH_WIDTH_ASCII 40 - printf("%-40s %s%s (%d subtrees)\n", + printf("%-" HASH_WIDTH_ASCII "s %s%s (%d subtrees)\n", This compiles, but I suspect that it's not going to do what I want it to do. It's something I've never been able to do in C - how does one get quotes around a defined value? I don't really want to resort to + printf("%-*s %s%s (%d subtrees)\n", HASH_WIDTH_ASCII, As that's a runtime change. Andy -- Dr Andy Parkins, M Eng (hons), MIEE andyparkins@gmail.com ``` ## Junio C Hamano, 2007-02-19 09:38 Subject: Re: Numeric constants as strings Message-ID: <7virdy8p25.fsf@assigned-by-dhcp.cox.net> URL: https://gitlist.dev/e/7virdy8p25.fsf%40assigned-by-dhcp.cox.net In-Reply-To: <200702190916.35813.andyparkins@gmail.com> ``` Andy Parkins writes: > I'm working on bringing my hash width literals patch up to > date now that 1.5.0 has passed. It's all been trivial apart > from one line: > > #define HASH_WIDTH_ASCII 40 > - printf("%-40s %s%s (%d subtrees)\n", > + printf("%-" HASH_WIDTH_ASCII "s %s%s (%d subtrees)\n", > > This compiles, but I suspect that it's not going to do what I > want it to do. Doesn't writing "foo" "bar" (two string literals next to each other) tell the compiler to concatenate them? ``` ## Junio C Hamano, 2007-02-19 09:49 Subject: Re: Numeric constants as strings Message-ID: <7vbqjq8ojr.fsf@assigned-by-dhcp.cox.net> URL: https://gitlist.dev/e/7vbqjq8ojr.fsf%40assigned-by-dhcp.cox.net In-Reply-To: <200702190916.35813.andyparkins@gmail.com> ``` Andy Parkins writes: > I'm working on bringing my hash width literals patch up to > date now that 1.5.0 has passed. I do not want to risk discouraging public discussion on this topic, but I am not sure if this is really worth it. It is not like if/when we find SHA-1 is inadequate we would just switch to SHA-256 and redefine HASH_BYTES from 20 to 32 and be done with it. With the need for backward compatibility, we would probably end up changing "unsigned char sha1[20]" to something that allows us to tell which hash function's result we are talking about, like: struct { enum { SHA_1, SHA_256 } type; union { unsigned char sha1[20]; unsigned char sha256[32]; } u; }; ``` ## Shawn O. Pearce, 2007-02-19 09:49 Subject: Re: Numeric constants as strings Message-ID: <20070219094955.GE30030@spearce.org> URL: https://gitlist.dev/e/20070219094955.GE30030%40spearce.org In-Reply-To: <7virdy8p25.fsf@assigned-by-dhcp.cox.net> ``` Junio C Hamano wrote: > Andy Parkins writes: > > > I'm working on bringing my hash width literals patch up to > > date now that 1.5.0 has passed. It's all been trivial apart > > from one line: > > > > #define HASH_WIDTH_ASCII 40 > > - printf("%-40s %s%s (%d subtrees)\n", > > + printf("%-" HASH_WIDTH_ASCII "s %s%s (%d subtrees)\n", > > > > This compiles, but I suspect that it's not going to do what I > > want it to do. > > Doesn't writing "foo" "bar" (two string literals next to each other) > tell the compiler to concatenate them? Yes, but here HASH_WIDTH_ASCII is a number... wtf is the compiler generating for the following? printf("%-" 40 "s %s%s (%d subtrees)\n", I did not even realize that was legal C... Now if the 40 was in quotes (e.g. "40") then the concatenate rule would apply and we would get a nice argument to printf. -- Shawn. ``` ## Matthieu Moy, 2007-02-19 10:01 Subject: Re: Numeric constants as strings Message-ID: URL: https://gitlist.dev/e/vpq1wkm31q4.fsf%40olympe.imag.fr In-Reply-To: <20070219094955.GE30030@spearce.org> ``` "Shawn O. Pearce" writes: > I did not even realize that was legal C... Now if the 40 was in > quotes (e.g. "40") then the concatenate rule would apply and we > would get a nice argument to printf. I suppose the solution is to use #HASH_WIDTH_ASCII to tell the preprocessor to put the quotes around HASH_WIDTH_ASCII. -- Matthieu ``` ## Mark Wooding, 2007-02-19 10:04 Subject: Re: Numeric constants as strings Message-ID: URL: https://gitlist.dev/e/slrnetitgs.sbe.mdw%40metalzone.distorted.org.uk In-Reply-To: <200702190916.35813.andyparkins@gmail.com> ``` Andy Parkins wrote: > I'm working on bringing my hash width literals patch up to date now > that 1.5.0 has passed. It's all been trivial apart from one line: > > #define HASH_WIDTH_ASCII 40 > - printf("%-40s %s%s (%d subtrees)\n", > + printf("%-" HASH_WIDTH_ASCII "s %s%s (%d subtrees)\n", The standard two-step goes #define STRINGIFY(foo) STRINGIFY_REALLY(foo) #define STRINGIFY_REALLY(foo) #foo The purpose of STRINGIFY_REALLY is to macro-expand the argument foo. If you just invoked STRINGIFY_REALLY printf("%-" STRINGIFY_REALLY(HASH_WIDTH_ASCII) "s %s%s (%d subtrees)\n", you'd get printf("%-HASH_WIDTH_ASCIIs %s%s (%d subtrees)\n", ... which is not what you wanted. However, printf("%-" STRINGIFY(HASH_WIDTH_ASCII) "s %s%s (%d subtrees)\n", will do the right thing. -- [mdw] ``` ## Andy Parkins, 2007-02-19 10:14 Subject: Re: Numeric constants as strings Message-ID: <200702191014.23055.andyparkins@gmail.com> URL: https://gitlist.dev/e/200702191014.23055.andyparkins%40gmail.com In-Reply-To: <7virdy8p25.fsf@assigned-by-dhcp.cox.net> ``` On Monday 2007 February 19 09:38, Junio C Hamano wrote: > > #define HASH_WIDTH_ASCII 40 > > - printf("%-40s %s%s (%d subtrees)\n", > > + printf("%-" HASH_WIDTH_ASCII "s %s%s (%d subtrees)\n", > > > > This compiles, but I suspect that it's not going to do what I > > want it to do. > > Doesn't writing "foo" "bar" (two string literals next to each other) > tell the compiler to concatenate them? It's not a string literal though. It's #define HASH_WIDTH_ASCII 40 rather than #define HASH_WIDTH_ASCII "40" I'm wondering how to turn the first into the second using the preprocessor. Andy -- Dr Andy Parkins, M Eng (hons), MIEE andyparkins@gmail.com ``` ## Andy Parkins, 2007-02-19 10:54 Subject: Re: Numeric constants as strings Message-ID: <200702191055.00203.andyparkins@gmail.com> URL: https://gitlist.dev/e/200702191055.00203.andyparkins%40gmail.com In-Reply-To: ``` On Monday 2007 February 19 10:01, Matthieu Moy wrote: > "Shawn O. Pearce" writes: > > I did not even realize that was legal C... Now if the 40 was in > > quotes (e.g. "40") then the concatenate rule would apply and we > > would get a nice argument to printf. > > I suppose the solution is to use #HASH_WIDTH_ASCII to tell the > preprocessor to put the quotes around HASH_WIDTH_ASCII. I'm afraid that only works when you're token pasting parameters in a #define macro. For example: #define macro(x) "foo" #x "baz" Then, macro(bar) expands to "foo" "bar" "baz". However, the following does not work: #define BAR bar #define macro "foo" #BAR "baz" This is because BAR is not a macro parameter. I've also tried it indirectly: #define BAR bar #define MAKESTRING(x) #x #define macro "foo" MAKESTRING(BAR) "baz" But this expands to "foo" "BAR" "baz". Also wrong. Equally, using # anywhere but during a #define doesn't work, so I can't simply write printf( "%-" #HASH_WIDTH_ASCII "s", string ); Woe is me. :-( Andy -- Dr Andy Parkins, M Eng (hons), MIEE andyparkins@gmail.com ``` ## Andy Parkins, 2007-02-19 11:00 Subject: Re: Numeric constants as strings Message-ID: <200702191100.42953.andyparkins@gmail.com> URL: https://gitlist.dev/e/200702191100.42953.andyparkins%40gmail.com In-Reply-To: <7vbqjq8ojr.fsf@assigned-by-dhcp.cox.net> ``` On Monday 2007 February 19 09:49, Junio C Hamano wrote: > I do not want to risk discouraging public discussion on this > topic, but I am not sure if this is really worth it. It's not primarily for that purpose, but rather to improve readability. For example, this little bit of patch: - if (get_sha1_hex(buffer+5, tree_sha1) || buffer[45] != '\n') + if (get_sha1_hex(buffer+5, tree_sha1) || buffer[HASH_WIDTH_ASCII+5] != '\n') return objerror(&commit->object, "invalid 'tree' line format - bad sha1"); - buffer += 46; + buffer += HASH_WIDTH_ASCII+6; while (!memcmp(buffer, "parent ", 7)) { - if (get_sha1_hex(buffer+7, sha1) || buffer[47] != '\n') + if (get_sha1_hex(buffer+7, sha1) || buffer[HASH_WIDTH_ASCII+7] != '\n') return objerror(&commit->object, "invalid 'parent' line format - bad sha1"); - buffer += 48; + buffer += HASH_WIDTH_ASCII+8; Using HASH_WIDTH_ASCII+8 is much clearer for a reader to be able to understand intent than 48. Especially when the variables in question are called "buffer" it's harder to track what is being stored in the buffer without a named constant. There are also a few other places where 20 is used and HASH_WIDTH_ASCII is not intended. Andy -- Dr Andy Parkins, M Eng (hons), MIEE andyparkins@gmail.com ``` ## Andy Parkins, 2007-02-19 11:02 Subject: Re: Numeric constants as strings Message-ID: <200702191103.00431.andyparkins@gmail.com> URL: https://gitlist.dev/e/200702191103.00431.andyparkins%40gmail.com In-Reply-To: ``` On Monday 2007 February 19 10:04, Mark Wooding wrote: > #define STRINGIFY(foo) STRINGIFY_REALLY(foo) > #define STRINGIFY_REALLY(foo) #foo > printf("%-" STRINGIFY(HASH_WIDTH_ASCII) "s %s%s (%d subtrees)\n", Ah ha! Magical. You've taught me something there. Thanks. Andy -- Dr Andy Parkins, M Eng (hons), MIEE andyparkins@gmail.com ``` ## Jakub Narebski, 2007-02-20 13:06 Subject: Re: Numeric constants as strings Message-ID: URL: https://gitlist.dev/e/ererl9%24df0%241%40sea.gmane.org In-Reply-To: <200702191103.00431.andyparkins@gmail.com> ``` Andy Parkins wrote: > On Monday 2007 February 19 10:04, Mark Wooding wrote: > >> #define STRINGIFY(foo) STRINGIFY_REALLY(foo) >> #define STRINGIFY_REALLY(foo) #foo >> printf("%-" STRINGIFY(HASH_WIDTH_ASCII) "s %s%s (%d subtrees)\n", > > Ah ha! Magical. You've taught me something there. Thanks. This trick is in the cpp documentation. (cpp.info.gz)Stringification -- Jakub Narebski Warsaw, Poland ShadeHawk on #git ```