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[eternal_noob]

How do I fit this square peg into the C++ hole?

For C++ you'd need to use a file extension suitable for C++, i.e. *.cpp or *.cc.
In addition, i'd use the C++ headers, e.g. <stdlib.h> becomes <cstdlib>, <stdio.h> becomes <cstdio> and so on.

Why don't this compile.

What's the exact error message?

 

[Phishfry]

I got it working. I only added code portion from libgpio manual. Needed more. There were two examples and I assumed wrong.

Found some good tutorials

Calling C Code from C++ With 'extern "C"' - Simplify C++!

Now and then we have the need to call functionality that was written in C from our C++ programs. For that, we need to use and understand `extern "C"`.

arne-mertz.de

He says not to use ifdef.

Mixing C and C++: extern C - Embedded Artistry

1 May 2017 by Phillip Johnston • Last updated 20 April 2022When transitioning from C to C++, you are not likely to refresh your entire code base. Instead, you will need to maintain a mix of C and C++ code, hopefully getting the two sets of code to work together. One common situation is that …...

embeddedartistry.com

This one says use it....
Oh boy.

 

[Phishfry]

Just to critique my learning I thought that the statement:

gpio_config_t was sufficent alone.

While the top part of the previous example was needed.

gpio_handle_t handle;
handle = gpio_open(0);

Compiler was complaining about handle undeclared.

In my head I was thinking device does not need to be opened to check config. That's why I ignored the top section of example.
That assumption was wrong.

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <libgpio.h>

    int main(int argc, char **argv)
    {
        gpio_handle_t handle;
        handle = gpio_open(0);
        gpio_config_t cfg;
        cfg.g_pin=31;
        gpio_pin_config(handle, &cfg);
        printf("Pin %d: \"%u\"\n", cfg.g_pin, cfg.g_flags);
};

 

[eternal_noob]

You need to destroy the handle using gpio_close(handle); after your're done. See gpio_close(3).

I suggest you use the full example code and not just parts of it.

 

[Phishfry]

OK now my dumb questions come. From everything I read for each programmatic OPEN you should do a CLOSE operation.

Why is there no gpio_close shown. That should be part of the function for a "One time call" right? If polling you might want to keep it open.

 

[Phishfry]

OK I see now. More stuff from top example I needed to scrape.
gpio_close(handle);

gpio

man.freebsd.org

 

[eternal_noob]

I would use a C++ wrapper class and open the handle in the constuctor and close it in the destructor. Then have wrapper methods for each operation you want to support.

 

[Phishfry]

Thanks for the assistance. I have researched wrappers and bindings and wondered about the cfltk project:

cfltk/examples/counter.c at main · MoAlyousef/cfltk

C Bindings for FLTK. Contribute to MoAlyousef/cfltk development by creating an account on GitHub.

github.com

 

[eternal_noob]

A C binding to a C++ library does not make sense imho. It only adds confusion to the project. Object orientation is one of the strengths of C++, and it should not be abandoned.

 

[Jose]

Thanks for the assistance. I have researched wrappers and bindings and wondered about the cfltk project:

cfltk/examples/counter.c at main · MoAlyousef/cfltk

C Bindings for FLTK. Contribute to MoAlyousef/cfltk development by creating an account on GitHub.

github.com

Mo is also active on the FLTK mailing list.

 

[Phishfry]

I am sitting here reflecting on my decision to use FLTK or anything not C.
Doing some Hello World with Motif. Playing with Xaw.

I feel like I have the GUI part down and now its meat and potatoes. FLTK meets my needs.
I can make GUI screens just like I could with MS Access but there is no SQL Query builder here.

I have the Community College course book open and looking at the offerings.
CSC 221 teaches with Python.
Ugg.
I do need the structure of a classroom. Dank old books and web pages just are not enough.