April 29, 2013

Casting in C++

As I most of my day time code in C, I used C-style casts in the beginning. The application was mixture of C and C++ (C++ API for C static library), therefore casts were needed (void pointer to data returned).

I corrected entire code, to replace with proper C++ casts. Because be aware of how C casts are interpreted in C++ language, they combine const_cast, static_cast and reinterpret_cast. One which works is used. Here are some disadvantages: hard to locate them, no compiler check, the ambiguity => not explicit, no dynamic runtime check (sometimes useful but costy - RTTI).

There are 4 casting operators  in C++: static_cast, const_cast, dynamic_cast, reinterpret_cast.

Small guide to casting in C++ [justcheckingonall.wordpress.com]
It gives an insight about C++ casting, 

April 22, 2013

Two sites with list of C / ARM / AVR books and tutorials.

While I was checking books which I would like to buy, I found these two webpages which share literature about C/embedded/signals.

Keil embedded bookshelf [keil.com/books]
 I had to ordered another two new books which I have not read yet, ARM assembly language and ARM system developer's guide. I can't wait to read them.

AVR freaks - Online C books and Tools [avrfreaks.net]
Rich list of many tutorials, books mostly for C lang, AVR related.

April 20, 2013

G++ and C static library with C files ( -x flag )

I faced one rather small problem which engaged me for a while. I ported C++ demo application to CodeWarrior 10.3 using g++. Linked library was compiled with gcc.
Linker was against me to build the demo. It shown undefined variable errors in static library (library plus some files which are outside of the library). I knew those undefined variables are properly declared and had to be visible to the linker. The output in a console was allright at first sight.

I explored linker settings in CW (not much to do with options there, preferably to use own linker commands). Did not do the trick. I proceeded to compiler, here's link which made it clear:

man gcc [cf.ccmr.cornell.edu/cgi-bin]

Particulary option -x none. I did not see any -x in the console output. Once I had added it into command line pattern, it linked.


April 13, 2013

Sublime Go to the definition - CTags

One of the two features I really appreciate during a development - Go to the definition. I had downloaded Ctags plugin but it did not work out of the box only because I did not know about downloading CTags (http://ctags.sourceforge.net).

Once you extract files, add a path to CTags in PATH inside Enviroment variables (for instance ;C:/Program Files/ctags). Open command line and type ctags. If an output is ctags: No files specified, we can proceed to the Sublime.

Click on any project opened in file browser there, first option should be CTags Rebuild tags. CTags creates two files in your project .tags_sorted_by_file and .tags. Use shortcut to GO TO THE DEFINITION is by default CTRL+SHIFT+. in windows. Awesome!

April 10, 2013

Compile time assertion in C lang

I planned to check more information about compilation assertion in C. How to check for size errors, alignments during compilation phase? The answer is compilation assertion which declares a variable which causes compilation error if the condition is true. Here are "simplest" one:

Checking sizeof at compile time [scaryreasoner.wordpress.com]
This article provides explanation of BUILD_BUG_ON macro which is used in linux for example. It can't be used in global scope because it's a statement.

Catching errors early with compile-time assertions [embedded.com]
Dan Saks article which solves the global scope problem with previous one,

#define compile_time_assert(cond, msg) \
  typedef char msg[(cond) ? 1 : -1]

Even though message is not shown in some IDEs, at least code line is thus it's easy to decipher it from the msg parameter why it caused an error.

April 2, 2013

Header circular problem ("impossible" errors received)

Once I moved only one include from the main code file to the main header file, I received weird errors from IAR:

Error[Pe020]: identifier "namespace" is undefinied
Error[Pe065]: expected a ";"
and so on...

My intuition was that it is header include problems. How could it scream namespace is undefined.
I corrected few includes in my application but still no success. The same application was successfully built in KEIL. I continued with removal all unnecessary includes until I found the one which caused all errors.

Lesson learned, time to do a review of our includes in all applications.