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Full Discussion: character I/O basics
Top Forums UNIX for Dummies Questions & Answers character I/O basics Post 44842 by Perderabo on Thursday 11th of December 2003 10:44:23 AM
Old 12-11-2003
starless, you really need to mention that you're using QNX. I guess that I shouldn't have remembered that you use QNX, but I didn't.

Your /dev/ser may indeed behave in ways that I don't understand. Or it may be very close to the unix tty. I'm not sure.

I'm not a c++ programmer nor do I know QNX. But I think that I understand this last character repeating business...maybe. But I'll have to explain unix system calls invoked from c.

I guessing that you're doing the equivalent of
read(fd, buffer, len)
and fd is now one side of a fifo. You need to change that to:
iret=read(fd, buffer, len)
if(iret == 0) { /* arrange to stop reading */ }
if (iret == -1) { /* error routine */ }

The read is failing, but you're not noticing this. Your buffer is not being touched. You're just assuming that it got a character. On unix, this situation would cause read to simply return a zero. In your case, you may being getting an error of some kind.

You can prove that you're not simply getting the last character... put some other character in the buffer just prior to the read. That will become the character that you seem to be reading in a loop.
 

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PERLQNX(1)						 Perl Programmers Reference Guide						PERLQNX(1)

NAME
README.qnx - Perl version 5 on QNX DESCRIPTION
As of perl5.7.2 all tests pass under: QNX 4.24G Watcom 10.6 with Beta/970211.wcc.update.tar.F socket3r.lib Nov21 1996. As of perl5.8.1 there is at least one test still failing. Some tests may complain under known circumstances. See below and hints/qnx.sh for more information. Under QNX 6.2.0 there are still a few tests which fail. See below and hints/qnx.sh for more information. Required Software for Compiling Perl on QNX4 As with many unix ports, this one depends on a few "standard" unix utilities which are not necessarily standard for QNX4. /bin/sh This is used heavily by Configure and then by perl itself. QNX4's version is fine, but Configure will choke on the 16-bit version, so if you are running QNX 4.22, link /bin/sh to /bin32/ksh ar This is the standard unix library builder. We use wlib. With Watcom 10.6, when wlib is linked as "ar", it behaves like ar and all is fine. Under 9.5, a cover is required. One is included in ../qnx nm This is used (optionally) by configure to list the contents of libraries. I will generate a cover function on the fly in the UU directory. cpp Configure and perl need a way to invoke a C preprocessor. I have created a simple cover for cc which does the right thing. Without this, Configure will create its own wrapper which works, but it doesn't handle some of the command line arguments that perl will throw at it. make You really need GNU make to compile this. GNU make ships by default with QNX 4.23, but you can get it from quics for earlier versions. Outstanding Issues with Perl on QNX4 There is no support for dynamically linked libraries in QNX4. If you wish to compile with the Socket extension, you need to have the TCP/IP toolkit, and you need to make sure that -lsocket locates the correct copy of socket3r.lib. Beware that the Watcom compiler ships with a stub version of socket3r.lib which has very little functionality. Also beware the order in which wlink searches directories for libraries. You may have /usr/lib/socket3r.lib pointing to the correct library, but wlink may pick up /usr/watcom/10.6/usr/lib/socket3r.lib instead. Make sure they both point to the correct library, that is, /usr/tcptk/current/usr/lib/socket3r.lib. The following tests may report errors under QNX4: dist/Cwd/Cwd.t will complain if `pwd` and cwd don't give the same results. cwd calls `fullpath -t`, so if you cd `fullpath -t` before running the test, it will pass. lib/File/Find/taint.t will complain if '.' is in your PATH. The PATH test is triggered because cwd calls `fullpath -t`. ext/IO/lib/IO/t/io_sock.t: Subtests 14 and 22 are skipped due to the fact that the functionality to read back the non-blocking status of a socket is not implemented in QNX's TCP/IP. This has been reported to QNX and it may work with later versions of TCP/IP. t/io/tell.t: Subtest 27 is failing. We are still investigating. QNX auxiliary files The files in the "qnx" directory are: qnx/ar A script that emulates the standard unix archive (aka library) utility. Under Watcom 10.6, ar is linked to wlib and provides the expected interface. With Watcom 9.5, a cover function is required. This one is fairly crude but has proved adequate for compiling perl. qnx/cpp A script that provides C preprocessing functionality. Configure can generate a similar cover, but it doesn't handle all the command- line options that perl throws at it. This might be reasonably placed in /usr/local/bin. Outstanding issues with perl under QNX6 The following tests are still failing for Perl 5.8.1 under QNX 6.2.0: op/sprintf.........................FAILED at test 91 lib/Benchmark......................FAILED at test 26 This is due to a bug in the C library's printf routine. printf("'%e'", 0. ) produces '0.000000e+0', but ANSI requires '0.000000e+00'. QNX has acknowledged the bug. AUTHOR
Norton T. Allen (allen@huarp.harvard.edu) perl v5.14.2 2011-09-26 PERLQNX(1)
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