I have 2 header files that have identical content:
template<typename T> inline void func(){
}
I include these 2 headers in a main.cpp file then I compile:
g++ main.cpp -o run
But I get:
In file included from main.cpp:2:0:
test2.cpp:1:34: error: redefinition of ‘template<class T> void func()’
template<typename T> inline void func(){
^
In file included from main.cpp:1:0:
test.cpp:1:34: error: ‘template<class T> void func()’ previously declared here
template<typename T> inline void func(){
What am I getting this error if use inline function which can be redefined?
You missing a key piece. The standard says in [basic.def.odr]/6 that
There can be more than one definition of a class type (Clause 9), enumeration type (7.2), inline function with external linkage (7.1.2), class template (Clause 14), non-static function template (14.5.6), static data member of a class template (14.5.1.3), member function of a class template (14.5.1.1), or template specialization for which some template parameters are not specified (14.7, 14.5.5) in a program provided that each definition appears in a different translation unit[...]
emphasis mine
So, you're allowed to have have multiple definitions of the inline function, but those definitions need to be in separate translation units(basically source files). Since they are in the same translation unit, they are violating that and you get an error.
Because of One Definition Rule (ODR).
In any translation unit, a template, type, function, or object can
have no more than one definition. Some of these can have any number of
declarations. A definition provides an instance.
You're only allowed to define a function once in a translation unit. There's no exception for inline functions (they do get an exception for being defined in separate TUs that are linked together).
What you should do is move the function definition to its own header file, which then gets included by the original 2 headers. Then you can put a header guard in the new file, so the function only gets defined the first time it's included.
