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.

const char* xyz = "xyz"; class Abc { public:     Abc()     {     } }; 

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

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";