How could I include a linux header file? I read from the web that the header file is in /usr/include. However, the header file I need is not in that directory; it is in /usr/src/kernels/2.6.32.../include/linux/.
I tried to include the file using the full path. However, the file itself includes other header files as well. Hence, the compiler couldn't find the other header files when I compile.
How could I include the header file in my program and compile the program?
You may add to your gcc command line -I (for "includes") options which specify other directories to search for include files (besides or actually even instead of the normal ones like /usr/include, though it's so long since I last needed the "instead of" that I don't recall how that's done == man gcc should tell you in 5 minutes if you need to find out;-).
If you are on Ubuntu, install libcpufreq-dev. This will give you the cpufreq.h header at /usr/include/cpufreq.h, which you can include from your code with #include <cpufreq.h>.
By default, gcc searches the following directories for header files:
/usr/local/include/
/usr/include/
and the following directories for libraries:
/usr/local/lib/
/usr/lib/
The compiler options -I and -L add new directories to the beginning of the include path and library search path respectively.