mingw32/bin/ld.exe ... undefined reference to [class] ... collect2.exe: error: ld returned 1 exit status

Question

Problem description while I am trying to move my code from Linux to Windows:

MinGW on Windows linker problems
happens when I am calling a user-defined class inside my Main.cpp ( works fine if I do not call the user-defined class constructor in Main )

Relevant code samples:

Person.hpp

class Person
{
    public:
        Person(const string& iName, 
                const list<string>& iContactDetails,
               ); 

        virtual ~Person(); 
        ...

Main.cpp

#include "Person.hpp"
...
int main()
{
...
Person myPerson = Person (myName, myContactDetails); //here is the linker problem
...
return 0;
}

Compilation command:

standalone

g++ -o MyProgram.exe Main.cpp -Wall

Makefile (tried even CC instead of CXX, or LDFLAGS=-lgdi32 instead of CXXFLAGS)

EXECUTABLE = MyProgram.exe

CXX = "C:\MinGW\bin\g++.exe"
CXXFLAGS = -Wall      // tried LDFLAGS=-lgdi32 as well

src = $(wildcard *.cpp)
obj = $(src:.cpp=.o)

all: myprog

myprog: $(obj)
    $(CXX) -o $(EXECUTABLE) $^ $(CXXFLAGS)

.PHONY: clean
clean:
    del $(obj) $(EXECUTABLE)

Error:

c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: C:\Users\....:Main.cpp:(.text+0x124c): undefined reference to `Person::~Person()'
collect2.exe: error: ld returned 1 exit status

As a summary, I encounter Linker problems during the MinGW G++ compilation step:

All external entity references are resolved. Library components are linked to satisfy external references to entities not defined in the current translation. All such translator output is collected into a program image which contains information needed for execution in its execution environment.

I tried to follow other similar problems, but they are unfortunately different issues:

How should I change my Makefile or my code? What flags does MinGW uses in Windows? Thank you very much

So where, in your opinion, is the code for the destructor? Can the compiler see it? It is e.g. not in the shown code. — Yunnosch, Jan 20 '20 at 17:52
Link 2., accepted answer, second link in the list, fourth code block. — Yunnosch, Jan 20 '20 at 18:00
actually, in the link there is a list of causes that trigger this linkage error. And in our case it should be: https://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix/12574400#12574400 Still, I do not know how to change the Makefile to refer the Person class ? — user3742309, Jan 20 '20 at 19:51

score 1 · Accepted Answer · answered Jan 25 '20 at 11:45

Same answer as I provided for How to correctly define and link a C++ class destructor to a main file?

I had the same problem as you. Try to move your constructor and destructor definition from the cpp into the header file. This way, the linkage is well done only by running the simple g++ command that you mentioned, you do not need a Makefile for this. The includes tell your compiler where to find the definitions.

Try:

MyClass(const string& className){ _className=className };

If the definition is inside the cpp file, I get the same error as you have.

But [shouldn't the implementation go in the cpp file](https://stackoverflow.com/a/583271/6243352)? — ggorlen, Feb 16 '22 at 04:38

mingw32/bin/ld.exe ... undefined reference to [class] ... collect2.exe: error: ld returned 1 exit status

1 Answers1

Linked