g++ linking order dependency when linking c code to c++ code

Question

Prior to today I had always believed that the order that objects and libraries were passed to g++ during the linking stage was unimportant. Then, today, I tried to link from c++ code to c code. I wrapped all the C headers in an extern "C" block but the linker still had difficulties finding symbols which I knew were in the C object archives.

Perplexed, I created a relatively simple example to isolate the linking error but much to my surprise, the simpler example linked without any problems.

After a little trial and error, I found that by emulating the linking pattern used in the simple example, I could get the main code to link OK. The pattern was object code first, object archives second eg:

g++ -o serverCpp serverCpp.o algoC.o libcrypto.a

Can anyone shed some light on why this might be so?. I've never seen this problem when linking ordinary c++ code.

question from:https://stackoverflow.com/questions/3363398/g-linking-order-dependency-when-linking-c-code-to-c-code

Answer 1

You can use --start-group archives --end-group and write the 2 dependent libraries instead of archives:

gcc main.o -L. -Wl,--start-group -lobj_A -lobj_b -Wl,--end-group