CODEWITHSUNDEEP
c++linkerarmmultiple-definition-error
learning_dude
learning_dude

Reputation: 1050

Multiple definition error is NOT happening when it should

I have a header header.hxx like this:

// header.hxx
#ifndef HEADER1
#define HEADER1
typedef struct s_ringreader{
  // some stuff in header
} RingReader;

RingReader defaultReader;

#endif

and multiple cxx like this, source1.cxx

// source1.cxx

# include "header.hxx"

void fun1(){
 // some stuff using defaultReader
}

, source2.cxx

// source2.cxx

# include "header.hxx"

void fun2(){
 // some other stuff using defaultReader
}

and source3.cxx

// source3.cxx

# include "header.hxx"

void fun3(){
 // some other stuff using defaultReader
}

My question is, should I not be getting mutliple definition errors, as I am including the header three times? Theoritically, in order for not getting this error I shoul use either static or extern for RingReader defaultReader but this is not happening.

As a note, this happens with some version of arm-poky compiler, but not with a different version. Is there any cases (like a different compilier) where these situations are not treated like errors?

Upvotes: 1

Views: 103

Answers (1)

Davis Herring
Davis Herring

Reputation: 39818

Since this code is valid C as well as C++, certain compilers will as an extension (C11 §J.5.11) interpret uninitialized global variables as common symbols. These act like C++17 inline variables and are merged at link time. This interpretation (like any other whatsoever!) is conforming for a C++ implementation since the program is ill-formed, no diagnostic required.

Upvotes: 0

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