For now I have added a warning that is issued (only) when there is definitely a problem (currently a read buffer, a pushback buffer or encoding conversion of the input). And I have added a similar warning for writing when there is encoding conversion of the output (writeChar). But, as you say, the behavior is undefined and it remains so regardless of whether there is a warning or not: programs should only use these functions with binary connections.
Best Tomas On 05/30/2018 12:00 AM, Aaron Goodman wrote: > Tomas, > > Thank you for the explanation. I see in the documentation: "These > functions are intended to be used with binary-mode connections." So I > see how using it on a text connection is undefined, and not a bug. An > error or warning when attempting to use a it on a text connection > would be helpful considering how the behavior has changed in R-3.5. > > On Tue, May 29, 2018 at 3:09 AM, Tomas Kalibera > <tomas.kalib...@gmail.com <mailto:tomas.kalib...@gmail.com>> wrote: > > On 05/26/2018 05:15 AM, Aaron Goodman wrote: > > I noticed an issue where readChar does not return the correct > value after a > call to readline. It appears that readChar is not aware of the > buffering, > so it reads from the end of the buffer, rather than the > current position in > the file. This is a significant change of behavior from R-3.4.4. > > Below is a test case that I used to home in on the problem. > > Thanks for the report and analysis, you are right, readChar > ignores the buffer (and it also ignores the pushback). But please > note that this behavior is in line with the documentation, see > ?readChar: readChar must only be used with binary connections, but > the example uses it on a text connection. Buffering and pushback > are only used on (readable) text connections. I will check whether > we could report a runtime error. > > Best > Tomas > > --- > > p<-"test2.txt" > cat("abcdefg > hijklmn > opqrstu",file=p) > > cat("read char after readline (h)\n") > con <- file(p,"r") > invisible(readLines(con,1)) > print(readChar(con,1)) > close(con) > > cat("read char after readline and seek (h)\n") > con <- file(p,"r") > invisible(readLines(con,1)) > invisible(seek(con,seek(con))) > print(readChar(con,1)) > close(con) > > cat("read lines after readline (hijklmn)\n") > con <- file(p,"r") > invisible(readLines(con,1) ) > print(readLines(con,1)) > close(con) > > > cat("read line after char (bcdefg):\n") > con <- file(p,"r") > invisible(readChar(con,1) ) > print(readLines(con,1)) > close(con) > > [[alternative HTML version deleted]] > > ______________________________________________ > R-devel@r-project.org <mailto:R-devel@r-project.org> mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > <https://stat.ethz.ch/mailman/listinfo/r-devel> > > > > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
