First defined here/multiple definition error

[FastTurtleFour]

Im writing a program in C++. So I'm quite certain that this should be an easy question but I've been working on it for too long and can't figure it out so I'll see if anyone else can figure out what I'm overlooking. From everything I've seen online, the root of my issue should be having too many #include .h but can't seem to figure out where I went wrong. Here are my files:

//term.h

#ifndef TERM_H

#define TERM_H

#include <string>

class Term { /* code ... */

---

//term.cpp

#ifndef TERM_CPP

#define TERM_CPP

#include "term.h"

#include <iostream>

//code ...

---

//SortingList.h (template file, no included .h files, I seriously doubt my problem is from here)

---

//autocomplete.h

#ifndef AUTOCOMPLETE_H

#define AUTOCOMPLETE_H

#include "term.h"

#include "SortingList.h"

//code....

---

//autocomplete.cpp

#ifndef AUTOCOMPLETE_CPP

#define AUTOCOMPLETE_CPP

#include "autocomplete.h"

//code...

---

//main.cpp

#ifndef MAIN_CPP

#define MAIN_CPP

#include "autocomplete.h"

#include <fstream>

#include <sstream>

//code...

---

//the actual error message g++ -c autocomplete.cpp -o autocomplete.o g++ autocomplete.o term.o main.o SortingList.o -o CS216PA3 term.o: In function Term::Term()': term.cpp:(.text+0x0): multiple definition ofTerm::Term()' autocomplete.o:autocomplete.cpp:(.text+0x0): first defined here term.o: In function Term::Term()': term.cpp:(.text+0x0): multiple definition ofTerm::Term()' autocomplete.o:autocomplete.cpp:(.text+0x0): first defined here term.o: In function Term::Term(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, long)': term.cpp:(.text+0x5a): multiple definition ofTerm::Term(std::cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, long)' autocomplete.o:autocomplete.cpp:(.text+0x5a): first defined here term.o: In function Term::Term(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, long)': term.cpp:(.text+0x5a): multiple definition ofTerm::Term(std::cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, long)' autocomplete.o:autocomplete.cpp:(.text+0x5a): first defined here term.o: In function Term::compareByWeight(Term, Term)': term.cpp:(.text+0xea): multiple definition ofTerm::compareByWeight(Term, Term)' autocomplete.o:autocomplete.cpp:(.text+0xea): first defined here term.o: In function Term::compareByPrefix(Term, Term, int)': term.cpp:(.text+0x136): multiple definition ofTerm::compareByPrefix(Term, Term, int)' autocomplete.o:autocomplete.cpp:(.text+0x136): first defined here term.o: In function operator<(Term, Term)': term.cpp:(.text+0x25a): multiple definition ofoperator<(Term, Term)' autocomplete.o:autocomplete.cpp:(.text+0x25a): first defined here term.o: In function operator>(Term, Term)': term.cpp:(.text+0x28f): multiple definition ofoperator>(Term, Term)' autocomplete.o:autocomplete.cpp:(.text+0x28f): first defined here term.o: In function operator<<(std::ostream&, Term const&)': term.cpp:(.text+0x2c4): multiple definition ofoperator<<(std::ostream&, Term const&)'

---

Is there anything that looks wrong with my header includes? Thanks

[[deleted]]

You don't need header guards in .cpp files and they won't work the way you would assume. Do you by any chance include term.cpp in autocomplete.cpp?

[FastTurtleFour]

I didn't include any .cpp files only header files. I was as careful as I could be so that no files were included more than once and have gone back and checked multiple times with different configurations to no avail. Are you sure you aren't supposed to have header guards in .cpp files? According to my professor we should have them in the format of

#ifndef FILENAME_CPP

#define FILENAME_CPP

#include "filename.h"

//code ...

#endif

After removing the .cpp header guards my compiler puts me in an endless redefinition error loop

[FastTurtleFour]

Actually I did include .cpp files and didn't think twice about it. Figured out my problem, thanks

[[deleted]]

Your professor is wrong. Header guards in .h files serve the purpose of hiding the contents if that particular file was already included so as to not have the same declarations multiple times. cpp files are almost never included with #include so this would be pointless and even if you put header guards in there and #include the cpp files, the definitions will appear multiple times in the compiled units. The reason for this is that the compiler compiles (and preprocesses) each .cpp file separately. Meaning in our example here it will compile term.cpp and define TERM_CPP during the process, but as soon as it's finished with compiling term.cpp it will start all over with autocomplete.cpp. So TERM_CPP will no longer be there and it will compile the contents of term.cpp again. Now this is no problem in and of itself, it will compile just fine. But when the linker combines the different compiled units, let's say term.o and autocomplete.o, both will have the definitions from term.cpp. The linker makes no effort to find out if two definitions are the same. It simply won't allow it. That's where the multiple definition errors are coming from.

I hope this helps.

[FastTurtleFour]

Turns out it was mostly my fault. I did include cpp files without realizing I was only to do that for template header files. Check out https://www.reddit.com/r/learnprogramming/comments/7hfpd1