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Reading the Serial Port

I've done a fair amount of Googling for information on reading the serial
port in C++ (and in Linux). Unfortunately, out of every 4 hits, 1 seems to
be an unanswered question, 1 is someone saying, "That's easy, there's a lot
out there, Google it,", 1 is a discussion on it without examples and the
other is who knows what.

I did find some info on it and have been experimenting. The one example
that I liked the best in terms of explanations and readability for a new
C++ programmer (coming over from Java and Perl) used this to open the
serial port (yes, with the .h on each include, I know it's older):

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <unistd.h>
int fd1;
fd1=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);

I understand the serial port will be binary and may be different from other
files, but I don't understand why this won't work just as well:

#include <iostream>
#include <fstream>

ofstream myfile;
myfile.open("/dev/ttyS0", ios::out | ios::binary);

Would that work as well or is there a reason for handling it the first way?
Basically, after I catch up on everything, one program will be reading the
serial port and reporting the output and another will be sending data to
the port. (It's possible, if I can ever find a good thread tutorial for
C++ that instead of different programs, they'll be different threads.)

Thanks for any help on the significance and differences of these two
methods!

Hal
Mar 11 '08 #1
9 14289
On Mar 11, 12:22 pm, Hal Vaughan <h...@halblog.comwrote:
I've done a fair amount of Googling for information on reading the serial
port in C++ (and in Linux). Unfortunately, out of every 4 hits, 1 seems to
be an unanswered question, 1 is someone saying, "That's easy, there's a lot
out there, Google it,", 1 is a discussion on it without examples and the
other is who knows what.

I did find some info on it and have been experimenting. The one example
that I liked the best in terms of explanations and readability for a new
C++ programmer (coming over from Java and Perl) used this to open the
serial port (yes, with the .h on each include, I know it's older):

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <unistd.h>
int fd1;
fd1=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);

I understand the serial port will be binary and may be different from other
files, but I don't understand why this won't work just as well:

#include <iostream>
#include <fstream>

ofstream myfile;
myfile.open("/dev/ttyS0", ios::out | ios::binary);

Would that work as well or is there a reason for handling it the first way?
Basically, after I catch up on everything, one program will be reading the
serial port and reporting the output and another will be sending data to
the port. (It's possible, if I can ever find a good thread tutorial for
C++ that instead of different programs, they'll be different threads.)

Thanks for any help on the significance and differences of these two
methods!

Hal
The C++ language has no concept of what a serial port is, therefor it
is off topic here. However, a newsgroup specific to your operating
system may very well hold answers for you.
Mar 11 '08 #2
Christopher wrote:
On Mar 11, 12:22 pm, Hal Vaughan <h...@halblog.comwrote:
>I've done a fair amount of Googling for information on reading the serial
port in C++ (and in Linux). Unfortunately, out of every 4 hits, 1 seems
to be an unanswered question, 1 is someone saying, "That's easy, there's
a lot out there, Google it,", 1 is a discussion on it without examples
and the other is who knows what.

I did find some info on it and have been experimenting. The one example
that I liked the best in terms of explanations and readability for a new
C++ programmer (coming over from Java and Perl) used this to open the
serial port (yes, with the .h on each include, I know it's older):

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <unistd.h>
int fd1;
fd1=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);

I understand the serial port will be binary and may be different from
other files, but I don't understand why this won't work just as well:

#include <iostream>
#include <fstream>

ofstream myfile;
myfile.open("/dev/ttyS0", ios::out | ios::binary);

Would that work as well or is there a reason for handling it the first
way? Basically, after I catch up on everything, one program will be
reading the serial port and reporting the output and another will be
sending data to
the port. (It's possible, if I can ever find a good thread tutorial for
C++ that instead of different programs, they'll be different threads.)

Thanks for any help on the significance and differences of these two
methods!

Hal

The C++ language has no concept of what a serial port is, therefor it
is off topic here. However, a newsgroup specific to your operating
system may very well hold answers for you.

So nobody here would have insight or help on reading from a device overall?
Or what the difference between the two methods are even if it's not just
Linux?

I'm sure an experienced C++ programmer could still give me some good info
about the two different ways to open a file/device that would help with an
overall understanding of the situation. I'm sure, for instance, that the
first method is not Linux specific and I know the 2nd one is not.

Hal
Mar 11 '08 #3
On Mar 11, 1:22*pm, Hal Vaughan <h...@halblog.comwrote:
I've done a fair amount of Googling for information on reading the serial
port in C++ (and in Linux). *Unfortunately, out of every 4 hits, 1 seemsto
be an unanswered question, 1 is someone saying, "That's easy, there's a lot
out there, Google it,", 1 is a discussion on it without examples and the
other is who knows what.

I did find some info on it and have been experimenting. *The one example
that I liked the best in terms of explanations and readability for a new
C++ programmer (coming over from Java and Perl) used this to open the
serial port (yes, with the .h on each include, I know it's older):

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <unistd.h>
int fd1;
fd1=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);

I understand the serial port will be binary and may be different from other
files, but I don't understand why this won't work just as well:

#include <iostream>
#include <fstream>

ofstream myfile;
myfile.open("/dev/ttyS0", ios::out | ios::binary);

Would that work as well or is there a reason for handling it the first way?
Basically, after I catch up on everything, one program will be reading the
serial port and reporting the output and another will be sending data to
the port. *(It's possible, if I can ever find a good thread tutorial for
C++ that instead of different programs, they'll be different threads.)

Thanks for any help on the significance and differences of these two
methods!

Hal
There is no reason that the ofstream cant be used. There are tons of
differences in how errors are handled, how formatted IO is handled,
and so forth. (the "ios::binary" will turn off some of the character
translations that go on between different encodings -- something you
dont need in serial ports)
The other differences is that once myfile goes out of scope, all
system resources will be released. And of course ofstream will format
your data into character based streams. If you really want to send raw
bytes through your serial port, avoid doing this
myfile<<data;
and do this instead:
myfile.write(&data,sizeof(data));

Hope that helps
Lance
Mar 11 '08 #4
Hal Vaughan <ha*@halblog.comwrote in
news:VvABj.5932$HA3.2326@trnddc02:
Christopher wrote:
>On Mar 11, 12:22 pm, Hal Vaughan <h...@halblog.comwrote:
>>I've done a fair amount of Googling for information on reading the
serial port in C++ (and in Linux).
Maybe the reason of your failure is that serial port is becoming
obsolete. Most peripheral devices are using USB nowadays. From your post
I gather that you are planning to make two threads in the same process
communicate over the serial port - why on the earth you would want to do
that?

[..]
>>Basically, after I catch up on everything, one program
will be reading the serial port and reporting the output and another
will be sending data to
the port. (It's possible, if I can ever find a good thread tutorial
for C++ that instead of different programs, they'll be different
threads.)
[...]
>
So nobody here would have insight or help on reading from a device
overall?
For interprocess or interthread communication you don't need any device!

Regards
Paavo
Mar 11 '08 #5
Paavo Helde wrote:
Hal Vaughan <ha*@halblog.comwrote in
news:VvABj.5932$HA3.2326@trnddc02:
>Christopher wrote:
>>On Mar 11, 12:22 pm, Hal Vaughan <h...@halblog.comwrote:
I've done a fair amount of Googling for information on reading the
serial port in C++ (and in Linux).

Maybe the reason of your failure is that serial port is becoming
obsolete. Most peripheral devices are using USB nowadays. From your post
I gather that you are planning to make two threads in the same process
communicate over the serial port - why on the earth you would want to do
that?
It's not failing, what I'm trying to understand is what is the difference in
the two methods? Are there things that won't show up in a simple test?
Are there implications in one method that aren't there in the other that
someone new to C++ won't think of without help?

Because that's where the device is I need to communicate with.

If I use a USB/Serial adaptor on a USB port, will reading and writing to the
USB port be just the same as to/from the serial port? (I would think so,
but I don't know if the USB/serial adaptor makes things different.)
[..]
>>>Basically, after I catch up on everything, one program
will be reading the serial port and reporting the output and another
will be sending data to
the port. (It's possible, if I can ever find a good thread tutorial
for C++ that instead of different programs, they'll be different
threads.)
[...]
>>
So nobody here would have insight or help on reading from a device
overall?

For interprocess or interthread communication you don't need any device!
Sorry, it's a separate issue and I was thinking of the whole thing together
and I shouldn't have combined the two in one post.

Hal
Mar 11 '08 #6
Lance Diduck wrote:
On Mar 11, 1:22*pm, Hal Vaughan <h...@halblog.comwrote:
>I've done a fair amount of Googling for information on reading the serial
port in C++ (and in Linux). *Unfortunately, out of every 4 hits, 1 seems
to be an unanswered question, 1 is someone saying, "That's easy, there's
a lot out there, Google it,", 1 is a discussion on it without examples
and the other is who knows what.

I did find some info on it and have been experimenting. *The one example
that I liked the best in terms of explanations and readability for a new
C++ programmer (coming over from Java and Perl) used this to open the
serial port (yes, with the .h on each include, I know it's older):

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <unistd.h>
int fd1;
fd1=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);

I understand the serial port will be binary and may be different from
other files, but I don't understand why this won't work just as well:

#include <iostream>
#include <fstream>

ofstream myfile;
myfile.open("/dev/ttyS0", ios::out | ios::binary);

Would that work as well or is there a reason for handling it the first
way? Basically, after I catch up on everything, one program will be
reading the serial port and reporting the output and another will be
sending data to the port. *(It's possible, if I can ever find a good
thread tutorial for C++ that instead of different programs, they'll be
different threads.)

Thanks for any help on the significance and differences of these two
methods!

Hal
There is no reason that the ofstream cant be used. There are tons of
differences in how errors are handled, how formatted IO is handled,
and so forth. (the "ios::binary" will turn off some of the character
translations that go on between different encodings -- something you
dont need in serial ports)
The other differences is that once myfile goes out of scope, all
system resources will be released. And of course ofstream will format
your data into character based streams. If you really want to send raw
bytes through your serial port, avoid doing this
myfile<<data;
and do this instead:
myfile.write(&data,sizeof(data));

Hope that helps
Lance
It helps a LOT!

Thank you!

Hal
Mar 11 '08 #7
Hal Vaughan <ha*@halblog.comwrote in news:dzCBj.3956$z13.99@trnddc06:
Paavo Helde wrote:
>Hal Vaughan <ha*@halblog.comwrote in
news:VvABj.5932$HA3.2326@trnddc02:
>>Christopher wrote:

On Mar 11, 12:22 pm, Hal Vaughan <h...@halblog.comwrote:
I've done a fair amount of Googling for information on reading the
serial port in C++ (and in Linux).

Maybe the reason of your failure is that serial port is becoming
obsolete. Most peripheral devices are using USB nowadays. From your
post I gather that you are planning to make two threads in the same
process communicate over the serial port - why on the earth you would
want to do that?

It's not failing, what I'm trying to understand is what is the
difference in the two methods? Are there things that won't show up in
a simple test? Are there implications in one method that aren't there
in the other that someone new to C++ won't think of without help?

Because that's where the device is I need to communicate with.

If I use a USB/Serial adaptor on a USB port, will reading and writing
to the USB port be just the same as to/from the serial port? (I would
think so, but I don't know if the USB/serial adaptor makes things
different.)
Sorry, I misunderstood your problem! I don't know answers to your
questions. Alas, the serial ports are outside of C++ and off-topic in
this ng, please try some linux newsgroup!

(I myself would go for POSIX open() route just to avoid any chances that
the C++ layer fails to provide some seemingly needed flags like O_NOCTTY
or O_NDELAY. But this would be non-portable of course.)

Regards
Paavo
Mar 11 '08 #8
Hal Vaughan wrote:

And some people decided that rather than try to provide helpful
information from the start and addressing the parts of my post they
could, that they'd rather just play Internet Policeman.
*plonk*

Brian
Mar 12 '08 #9
Christopher wrote:
On Mar 11, 1:50 pm, Hal Vaughan <h...@halblog.comwrote:
>fd1=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
>ofstream myfile;
>myfile.open("/dev/ttyS0", ios::out | ios::binary);
Sure, the first is C and the second is C++.
Not even that. The first is POSIX, which happens to have a C API. It's
no more a C function that it is a C++ one.


Brian
Mar 12 '08 #10

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