Question

I’m currently running a c++ project, with a class called Relation.

I’m trying to compile it, but I constantly get this error, regardless of the file extension that I’m using.

Compiler is cc, and the class I’m trying to compile, even when empty as below, causes this error.

I’ve tried the c++ header extensions, and the same errors occur.

#ifndef RELATION_H_
#define RELATION_H_

class Relation {
public:
Relation();
virtual ~Relation();
};

#endif

Answer 1

That’s the error you get when you try to compile C++ code with the C compiler.

pax$ cat qq.cpp
class Relation {
public:
    Relation();
    virtual ~Relation();
};

pax$ g++ -c -o qq.o qq.cpp

pax$ cp qq.cpp qq.c

pax$ gcc -c -o qq.o qq.c
qq.c:4: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'Relation'

You should check that your cc compiler is actually capable of compiling C++ and what, if any, options are needed to make it do so.

If it’s gcc (and it certainly looks like it is, based on the absolutely identical error message), you may need to make sure that you’re calling g++ rather than gcc and/or that your extension for the source file (not header) is a recognised one, like .cpp ^(a).

I’m not entirely certain the rules that gcc follows but I’ve always found it safer to use source files like blahblah.cpp and explicitly use g++.

---

^(a) Reasoning: since you mention in your particular case that you’re using the correct header file extensions, I think one possibility is that the header extension has no effect whatsoever on what gcc tries to compile the source file as. It uses only the source file extension, as per the following transcript:

pax$ cat xyzzy.hpp
class Relation {
public:
    Relation();
    virtual ~Relation();
};

pax$ cat plugh.c
#include "xyzzy.hpp"

pax$ gcc -c -o plugh.o plugh.c
In file included from plugh.c:1:
xyzzy.hpp:1: error: expected '=', ',', ';', 'asm' or '__attribute__'
                    before 'Relation'

pax$ cp plugh.c plugh.cpp

pax$ gcc -c -o plugh.o plugh.cpp

In other words, I don’t think having an included header file of (for example) xyzzy.hpp would force the compiler to compile C++ if the source file that’s including it is still plugh.c.