duplicate symbol error C++

Question

I have added some const character in my file as under. The error i get is duplicate symbol _xyz(say). What is the problem with it and how could i get out of this.

Answer 1

If this is in a header file, you're defining xyz every time you #include it.

You can change the declaration as @R Samuel Klatchko shows. The usual way (if the data isn't const) is like this:

In Abc.h:

extern char *xyz;

In Abc.cpp:

char *xyz = "xyz";

Edited to add

Note that header guards will not solve this problem:

#ifndef XYZ_H
#define XYZ_H
...
#endif

Header guards prevent "redefinition" errors, where the same symbol appears twice in the same compilation unit. That's a compiler error.

But even with header guards the definition of xyz will still appear in every source file that includes it, causing a "duplicate symbol" error, which is a linker error.

It would have been more helpful if the original poster had mentioned that, of course.

Answer 2

I also ran into this issue, but for me the solution was different. I had put overloaded operators (==, !=, <<) in my header file and implemented them. This was causing an issue in other files where I also used ==, !=, or <<. To solve this, I moved the implementation into the .cpp file and left the declaration in the header file.

Answer 3

The problem is every source file that includes your header file gets it's own copy of xyz with external linkage.

The easiest way to fix that is to give xyz internal linkage. You can do that by making the pointer itself const in addition to having the underlying char's const:

const char* const xyz = "xyz";

Answer 4

Please, provide a meaningful description of the problem. What's "my file"? What "const character" are you taking about?

For what you provided so far I can only guess that you added the above definition of xyz to a header file and then included it into several translation units. The result: object xyz got defined more than once. Hence the error.