C++ inlining class methods causes undefined reference

Question

I'm getting a compiler error when I try to inline a method of one of my classes. It works when I take away the "inline" keyword.

Here's a simplified example:

main.cpp:

#include "my_class.h"  int main() {   MyClass c;   c.TestMethod();    return 0; } 

my_class.h:

class MyClass {  public:   void TestMethod(); }; 

my_class.cpp:

#include "my_class.h"  inline void MyClass::TestMethod() { } 

I try compiling with:

g++ main.cpp my_class.cpp 

I get the error:

main.cpp:(.text+0xd): undefined reference to `MyClass::TestMethod()' 

Everything is fine if I take away the "inline". What's causing this problem? (and how should I inline class methods? Is it possible?)

Thanks.

Answer 1

The body of an inline function needs to be in the header so that the compiler can actually substitute it wherever required. See this: How do you tell the compiler to make a member function inline?