Undefined reference/unresolved external symbol errors in C++/C/Objective-c and ways to solve/avoid them.

These specific errors occur at the last stage of Compilation, The stage is also called linking stage. As the name suggest all the code(implementation files) has been converted into object file or libraries. Now compiler wants to link them all together.

for a small example, A developer has defined one symbol SYM in a class TEST1 and you declared it in class TEST2. Linking phase has the responsibility to make sure call to that symbol finds valid symbol and…