gcc - linker error that makes no sense

Question

Using the Makefile provided by the Pi GPIO library, I made the libpigpio.so shard object using:

# from line 119 in make file
make libpigpio.so 

The shared object is created fine. The Makefile first created the pigpio.o object, then the command.o object, and links them together as a shared object. So far so good!

I wrote a very small main function that calls the gpioInitialise and gpioGetPWMfrequency.

It doesn't really matter which functions, what's important is they are defined in pigpio.h and written in pigpio.c.

Meaning the shared object should have them.

The compile command for my code is:

 gcc -Wall -pthread -fpic -L. -lpigpio -o drive drive.c 

Still I get the undefined reference error to both those functions.

It makes no sense! If it didn't find the shared object, it would reject the command. I also tried it -l:libpigpio.so and still the same problem.

I am compiling directly on the Rpi A+ (not using a cross compiler). So it should work!

What am I missing here?

Answer 1

It is a link order question. Please try the flowing command.

gcc drive.c -Wall -pthread -fpic -o drive -L. -lpigpio

you can read Why does the order in which libraries are linked sometimes cause errors in GCC? for more details.