C++ - /tmp/cckpbRW.o:main.cc:(.text+0x9d):undefined reference [duplicate]

Question

This question already has an answer here:

• What is an undefined reference/unresolved external symbol error and how do I fix it? 32 answers

Following the example here: http://www.learncpp.com/cpp-tutorial/19-header-files/

Relating to add.h and main.cpp

When I try to compile main.cc (I just used another extension), I get the following:

/tmp/cckpbRW.o:main.cc:(.text+0x9d):undefined reference to 'add(int, int)' collect2: ld returned 1 exit status

How can I fix this issue?

Thanks.

Answer 1

Your didn't link your main object to your add one, so when the linker tries to build the executables it cannot find the definition of symbol add(int, int) it uses.

You should compile main object, add object and link them together, like this:

g++ -c -o main.o main.cpp
g++ -c -o add.o add.cpp
g++ -o executable main.o add.o

or

g++ -o executable main.cpp add.cpp

this will compile add.cpp and main.cpp together

Answer 2

Looks like you are not linking the second .cpp file into final executable. Either compile and link them at the same time:

$ c++ -Wall -Werror -pedantic -g -otest1 add.cpp main.cpp

or compile them separately and then link:

$ c++ -Wall -Werror -pedantic -g -c main.cpp
$ c++ -Wall -Werror -pedantic -g -c add.cpp
$ c++ -Wall -Werror -pedantic -g -otest1 add.o main.o