On 19 October 2016 at 11:42, Steve Petrie, P.Eng. wrote: > // Define static members in file scope. > int sub1::sub1_int; > int* sub1::sub1_ptr_int = &sub1::sub1_int; > sub0 sub1::*sub1_ptr_sub0; This line doesn't do what you think it does. You've declared sub1_ptr_sub0 as a global variable of type sub0 sub1::* i.e. a pointer to data member. It should be: sub0* sub1::sub1_ptr_sub0; > So, my question is: > > Why does the program (main.cpp, testns_main.cpp) build and run OK, when line > 32 is commented out, so there is no use of the variable (repeated here from > line 32): > > sub1Object.sub1_ptr_sub0 = NULL; > > that points to objects of class sub0? > > But when line 32 is not commented out, the build of the program fails in the > linker step, with an "undefined reference" error: > > obj\Debug\testns_main.o: In function `ZN7ns_main16testns_main_funcEv': > F:/U S R/A S P/DIGDIG/CodeBlocks > Projects/dbxdig/dbxdig_test_ns/dbxdig_testns_main/testns_main.cpp:32: > undefined reference to `sub1::sub1_ptr_sub0' > > Why ??? Because you didn't define that one.
