Cross-platform development

During the course of developing Biarri’s flagship Workbench product, we’ve taken pains to ensure that our (GUI-less) optimisation “engines” work well under both Windows and Linux operating systems (so-called cross-platform). This turns out to be relatively easy as long as you stay away from the big OS-specific frameworks (e.g. Microsoft’s MFC/COM/ATL etc). We’ve picked up some handy tips along the way, particularly applicable to C++ development, which are worth sharing here.

• Be aware of differences in line endings – Windows uses carriage return and line feed \r\n, while Linux/Unix uses just line feed \n. (Note that Visual Studio will show files with Linux line feeds correctly, but Notepad won’t – this is one way to tell what line endings your file has in Windows). This can be particularly important when importing data e.g. into databases where the file originates from another OS.

• Always use forward slashes for file paths, not backslashes. Also, file names and folder paths are case sensitive under Linux but not under Windows. And don’t assume there is a C: or D: drive!

• You may have to be careful writing to temporary files and folders. In Linux /tmp is often used; in Windows /[user]/AppData/local/temp (location of the TEMP environment variable – e.g. type “%TEMP%” into the start menu or Windows Explorer). For Linux, it is sometimes necessary to manipulate a folder’s “sticky bit” to ensure that the folder is accessible by other users (e.g. a Postgres database user) – e.g. in Python:

• Be aware of the differences in file permissions in Windows and Linux. In Linux files have an “executable” bit. chmod a+x [file] makes a file an exe, which can then be run with “./filename”.

For C++ development:

• Name all cpp and h files in lower case if possible. Files are case sensitive in Linux and this includes #include’s!

• For compiling with GCC under Linux, the last line in a C++ file must be blank.

• In Linux C++ programs, general exception handling with catch(…) does not work. You can use sighandlers instead (see this for example), though it’s not as good – it is more equivalent to an exit(), with a chance to clean up.

• Beware doubles comparisons and inequality checking, at least in C++ programs. Always use a delta i.e. A == B may not be the case in both Windows and Linux if they are essentially the same number so use fabs(A – B)

• Build tips for Linux: Type “make” when you are in the directory to build the project. This will search for a file called “Makefile” and run it. (Use “make -f filename” to make from a different makefile). To force a recompile you can “touch” a file using “touch filename”.
  To clean out all object files type “make clean” (as long as your make file defines what cleaning does…). Use “make -j4” to run make with for concurrent jobs, to take advantage of multicore.

• In bash, to get a recursive line count of .cpp/.h files: find [directory] -type f -name *.cpp -exec wc -l {} \; | awk ‘{total += $1} END{print total}’

• Differences for GCC 4.3 compiler (e.g. compared to version 4.2.4): http://gcc.gnu.org/gcc-4.3/porting_to.html. (To check your version of GCC, type gcc -v).