Tricks every C programmer should know

I compiled a list of notes while reading a book called “Advanced Linux Programming”. I already knew some of those, but rarely keep in mind while doing development. Others, I didn’t have any idea they existed! Here’s the list (still expanding in my laptop):

• You can #define variables in the command line while compiling through GCC. For example, to define NDEBUG while compiling a test.c file do:
  gcc -o out -D NDEBUG test.c
gcc -o out -D NDEBUG=3 test.c
• Compile C programs with -O2 for production binaries.
• Learn to use GDB, especially for quickly finding Segmentation Faults.
• Use getopt_long() for command-line arguments parsing, instead of trying to parse them manually. Very handy!
• stdout is buffered, stderr is not! Which means writing to stderr will immediately be flushed. Writing to stdout, however, will be buffered until later or until a call to fflush(stdout).
• Use mkstemp() and tmpfile() for generating random file names for temporary files.
• Using abort() will generate a core-dump.
• If the library has both an archive (.ar) version and a shared object (.so) version, the program can be linked to the archive using -static. But by default, the shared object version is used.
• The libraries are searched in the current directory first by GCC during compilation.
• Using ldd binary_name will list all needed shared object it needs at runtime. It also lists indirect dependencies, i.e. libraries needed by the directly used libraries.
• A binary can be forced to look for the shared object in a directory using gcc -o app app.c -Wl,-rpath,/path/to/lib/directory. Defining LD_LIBRARY_PATH environment variable is another solution.
• Upgrading shared libraries doesn’t require the binaries to be recompiled/relinked etc.
• Static linking to libraries is good in scenarios where binaries will be installed in a non-privileged environment. So you don’t need sudo make install or sudo apt-get install something.
• Use ps -o pid,ppid,command to get process IDs, and the respective parent process IDs
• Another useful output ps can give is the start time of the process. Use ps -o start_time,command to get the list.