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Date: Sun 23-Sep-1989 21:55:08 From: Unknown Subject: Re: Variable Length Argument Lists for Methods--REPOST In article <1989Sep13.025245.1193@lighthouse.com>, I wrote what follows. However, no one seems to have responded. We're still looking for answers... >We're trying to write a method that takes a variable number of >arguments, something like: > >[error notify: "Error at line %i in file %s", __LINE__, __FILE__]; > >or > >[error notify: "Error: %s at line %i in file %s", "Big Bummer", >__LINE__, __FILE__]; > >We've settled on > >- error: (char *)format, ...; > >in our .h file (based on selectorRPC:paramTypes:... in Speaker.h), but >we haven't stumbled onto how to write the method. > >On page 4-13 of the Objective-C Compiler User Reference Manual (in >Volume 3 of the NeXT 0.9 Technical Documentation) is written > >- error:( char * ) format ; int aList ; >// ^ >// might be a colon; can't tell > >However, this results in a compiler error. > >We've tried variations on the ANSI stdarg technique, and we've tried >messing directly with pointers, to no avail. > >In our .m file, we can use > >- error: (char *)format, ... >{ > char *args; > char **scary; > char out[255]; > > scary = &format; > scary++; > args = *scary; > > sprintf(out, format, args); > NXAlert(out, "OK", NULL, NULL); > > return self; >} > >without getting a compiler error, but it dumps core in sprintf. > >Hints and code fragments would be greatly appreciated. Thanks, Brian Skinner Lighthouse Design, Ltd. >From: epsilon@wet.UUCP (Eric P. Scott)
Date: Sun 28-Sep-1989 02:47:49 From: Unknown Subject: Re: Variable Length Argument Lists for Methods--REPOST [I actually posted an answer from NeXT a few days ago, but I think the message never made it anywhere. So here it goes again; if you see this twice, apologies... -Ali] In article <1989Sep23.215508.5568@lighthouse.com> Brian Douglas Skinner writes: >We're trying to write a method that takes a variable number of >arguments, something like: > >[error notify: "Error at line %i in file %s", __LINE__, __FILE__]; Use of variable length argument lists is described in the Second Edition of Kernighan & Ritchie; you can use the same sort of mechanism to go through the arguments in ObjC. Say you have (very simple) method which takes a number and that many string arguments, and prints the strings one after another. The declaration would be: - listItems:(int)numItems, ...; ... the code itself would be: - listItems:(int)numItems, ... { va_list ap; va_start (ap, numItems); // Make ap point to the first unnamed argument printf ("The Items are: "); while (numItems--) printf ("%s ", va_arg(ap, char *)); // All args should be char * printf ("\n"); va_end (ap); // Wrap it up... } ... and a sample call could be: [self listItems:3, "foo", "bar", "zap"]; The above example is of course too simple; on page 156 of K&R there's a more complicated example that implements a minimal printf. If you just want to have an error: method that takes a format string and bunch of args and treats them like printf would, you can vfprintf (or vsprintf). The man page has the necessary info... Ali Ozer, NeXT Developer Support Ali_Ozer@NeXT.com >From: dcj@flume.ZK3.DEC.COM (Dave Jedlinsky OSEM)
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