I've been trying to track down some of the issues with command line length limits, and those writing GUIs/front-ends need to pay some attention to the issue.
src/unix/system.txt says * int R_ReadConsole(char *prompt, char *buf, int buflen, int hist) * * This function prints the given prompt at the console and then * does a gets(3)-like operation, transferring up to "buflen" characters * into the buffer "buf". The last two characters are set to "\n\0" * to preserve sanity. but that isn't actually true for some of the standard interfaces and seems undesirable. (Also, for 'characters' read 'bytes'.) What happens is that all calls to R_ReadConsole have buflen=1024. (These can be an input line of R code, or from scan() or from a stdin() connection.) If this is command input, the result is parsed, and if incomplete and not an error, more input is requested until it is complete. Suppose the user entered a very long line. Should the first 1024 bytes be syntactically complete, this will not do what he expected and it will be as if a LF had been inserted after 1024 bytes. But that is unlikely, and he may well get away with it, unless R_ReadConsole did actually does as documented and inserts "\n\0" (the Rgui and readline consoles do, but reading from a file in Linux or Windows does not). It seems the correct advice is that R_ReadConsole should only send a "\n" when there is no more input available, e.g. on EOF. I am changing the calling code to have a 1025 char buffer with last '\0' to ensure null-termination. Some consoles try to ensure that the user cannot enter more than 1024 bytes. That's a bit awkward in a MBCS, and also when input is being pasted in (possibly in the middle of a line). Generally this does not work too well: e.g. the readline console truncates at 1022 chars and appends a \n. I have no idea how an R user was expected to know there was a line limit. I've added some documentation to R-intro (but I will need to correct it as I didn't know the readline console used 1022). The limit applies to redirected input from a file, but not to source(). GUI writers: please take a look at how your interface handles very long input lines, particularly quoted strings (which seem the most likely reason for long lines). -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
