C++11 multiple definitions of class function

Question

RESOLVED: I'm a complete doofus. After pouring through all the files carefully and tracing back through our proprietary dependency file generator, it turns out that there were indeed rogue .cpp includes that had recently been added into the file system, and that was causing the issue. Sorry, and thanks for all the help everyone! XD

I'm having a frustrating difficulty with an obscure bug I was hoping someone could help with. Basically, I'm declaring a generic class in a header file like so:

//foo.h
#pragma once

class foo
{
  public:
    foo();
    ~foo();
    void random_function();
};

Note that I've declared pragma once to prevent multiple definitions, and all function prototypes are placed in class definition. The corresponding class is defined like so:

// foo.cpp
#include "foo.h"

foo::foo() {
}

foo::~foo(){
}

void foo::random_function(){
//do stuff
}

This class gets used in quite a number of other files. For example:

// bar.h
#include “foo.h”

class bar
{
  bar();
  ~bar();
  std::shared_ptr<foo> get_foo();
  std::shared_ptr<foo> my_foo;
};

But when I compile, I get the following error for each function member of the class definition:

bar.o: In function `foo:foo()':
dir/foo.cpp:80: multiple definition of `foo::foo()'
blah.o:dir/foo.cpp:80: first defined here
bar.o: In function `foo:foo()':
dir/foo.cpp:80: multiple definition of `foo::foo()'
blah.o:dir/foo.cpp:80: first defined here

Note how it appears to repeat the same 3-line error twice in a row. This same error pattern is repeated for every constructor/destructor/function declaration. Also note how it appears to be saying that the function foo() in foo.cpp is first defined in foo.cpp, which does'nt seem to make much sense. But I just noticed, that it starts with bar.o and then says blah.o...?

Really scratching my head on this one, can't seem to decipher where the issue is coming from or where I should look. Any help would be greatly appreciated! :D

Addendums:

• I can't post original code because it's from my work. I hope this example snippet is sufficient to at least give some direction as to where I should probably start looking, barring any issues with the code as it is currently set up.
• I'm not including any .cpp files elsewhere in the code. I only include .h.
• Original code has semicolons at end of header file class declarations, just forgot to include in example posted here. Updated to reflect that.
• Include of foo.h is consistent across all files (no accidental mixed casing).
• Other similarly defined classes are using this exact same pattern, but strangely are not generating the same error. :?
• To reiterate, I'm sure that I'm not #include'ing any .cpp files anywhere in my program, only header files are ever included elsewhere in the program.
• I am also sure that the constructor is declared in the header file as foo(); like in the above code example, and not foo(){}.
• Compiler supports pragma once (using g++).
• Fixed another typo in the above example not found in original code (quotation marks around header filename)
• The system I'm working on is actually quite large. There are many includes and dependencies throughout the code (even some circular dependencies) and the use of some singletons that are passed about throughout the system. The above example is a simplified representation of the issue I'm seeing at its most fundamental level, the above error I'm seeing is actually being generated for a number of new files I've been merging into the system (not just one). Strangely, other files that I've defined after a similar fashion are not and have not hitherto generated this issue, which is why I'm confused that it appears to be causing problems now.

Answer 1

Try adding in foo.h

#ifndef FOO_H
#define FOO_H

//foo class and stuff

#endif