c++ - Multiple definition of a variable in C++ classes

Question

Assume these two cpp files:

0.cc

#include <iostream>

class test{
 public:
 int num = 5;
};

int main(){
 test t;
 return t.num;
}

1.cc

class test{
 public:
 int num = 6; // <-- note this has a different value.
};

We compile it with g++ 0.cc 1.cc.

Initializing a member variable inside the class works since C++11. My question is how is it compiling whiteout a linker error? is it undefined behaviour? as we are breaking the one definition rule. If classes were not used this would generate a link error at compile time.

I know that defining a function within a class makes it inline so it would be ok to have multiple of them in different files, but not sure how multiple variables are ok?

标签： c++

Answer 1

是的，这违反了One Definition Rule并且是Undefined Behavior。