Undefined reference to func 'abc'

Question

I might not be able to give full code but I could create a smaller situation. I have an api, say abc which is declared as below in abc.h

extern int abc ( int x, int y = 0);

This api is used at multiple files such as x.cpp, y.cpp and z.cpp.

In file, z.cpp I wanted to use this api along with passing one extra paramter to it. So, I have changed the declaration inside abc.h as :

extern int abc ( int x, int y = 0, int z = 0)

This way, I would not need to change the call to these api calls at files x.cpp and y.cpp. Right? I could easily do my work under 'z' inside definition of abc api. Something like:

int abc(int x, int y, int z) {
  ...
  ...
  if (z) {
    <do_whatever>
  }
}

But when I compile it, I see 'undefined reference to `abc' at files x.cpp & y.cpp. What is happening?

Show us the code where the errors are, and the full text of the error message — Caleth, May 11 '18 at 09:59
@jarod - Ah, I read it as adding a new declation inside z.cpp. Now the new guess is that not all cpp files were recompiled to see the change. — Bo Persson, May 11 '18 at 10:09
Just to make it clear, what IDE are you using? Do you write some kind of Makefiles by yourself? — xvnm, May 11 '18 at 10:09
@JoseFelipe, From x.cpp & y.cpp, It gets called as : abc(1) or abc(1, 1) — Hemant Bhargava, May 11 '18 at 10:59
@Jarod42, I have changed the same declaration and definition. — Hemant Bhargava, May 11 '18 at 10:59
@HemantBhargava Vim is not an IDE, it's just a text editor with only itself. I asked because the error occurs when you uses Makefiles and modifies header files, since compiled object files was going to be linked to functions that was not modified, but then there's not. — xvnm, May 11 '18 at 18:57

score 3 · Accepted Answer · answered May 11 '18 at 10:38

3

This way, I would not need to change the call to these api calls at files x.cpp and y.cpp. Right?

You are right that you don't have to change the calls in x.cpp and y.cpp.

However, you still need to recompile them, otherwise you will get the link editor errors that you mention. Ideally your build system should see that x.o and y.o are dependencies of abc.h and that if the header changes both object files need to be regenerated.

answered May 11 '18 at 10:38

Paul Floyd

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Thank you. I get this point. It solved my problem as well. – Hemant Bhargava May 11 '18 at 11:01

Undefined reference to func 'abc'

1 Answers1