CODEWITHSUNDEEP
c++undefined
user1181459
user1181459

Reputation: 1

C++ "undefined reference to" function error

I've been having some problems compiling this code for mergesort on an array of custom data types. The undefined reference is in response to 

mergesort(hw1type*, int)

Here are the relevant code snips leaving out the includes, and what not, which I know all work:

Main (Where the error is propagating to):

hw1type * unsorted_array2 = new hw1type[SIZE];

unsorted_array2 = create_random_hw1type(SIZE);

mergesort(unsorted_array2, SIZE);

mergesort.h:

hw1type* mergesort(hw1type*, int);
hw1type* merge(hw1type*, int, hw1type*, int);

mergesort.cc:

hw1type mergesort(hw1type* unsorted_array, int n)

I can't see anything wrong with the way the functions are declared, or the way I'm passing the variables in main. But, it's been a while since I've used c++ so I could use a second or third pair of eyes!

Edit: Turns out it was the make file, I forgot to change. It's always something simple.

Ah, right, I was using the standard make file that came with the other classes.Anyway, here's that code:

I should probably throw mergesort.o into the list of OBJs, but anything else? The make file looks like this: 

CC=gcc
CXX=c++
CFLAGS=-ggdb -O3 -I. 
LDFLAGS=-L. -lcs600

OBJ=timer.o random_generator.o sort.o

cs600:  libcs600.a main.o
    $(CXX) $(CFLAGS) main.o -o hw1 $(LDFLAGS)

libcs600.a: $(OBJ)
    ar ru libcs600.a $(OBJ)
    ranlib libcs600.a

.cc.o:
    $(CXX) -c $(CFLAGS) $<


clean:
    @rm -f *.o
    @rm -f libcs600.a
    @rm -f hw1

I need to add mergesort.o to the OBJ field, but anything other than that? Considering it's been a while for C++, it's really been a while since I've messed around with make files.

Upvotes: 0

Views: 5276

Answers (2)

Adam Rosenfield
Adam Rosenfield

Reputation: 400284

You're not compiling mergesort.cc into object code, and/or you're not linking in that object code.

If you're using an IDE, make sure you've added mergesort.cc to your project configuration; if you're using Makefiles or compiling on the command line, make sure you include that in the list of source files you're compiling.

Upvotes: 0

Carl Norum
Carl Norum

Reputation: 224944

"Undefined reference" is a link-time error. Make sure the object file that contains the missing function is part of your link command line. In your case, probably something like:

clang++ -o app main.o mergesort.o

Or simply:

clang++ -o app main.cc mergesort.cc

If you didn't compile each file separately first.

Upvotes: 1

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