C++ inlining class methods causes undefined reference

c++ inline
FrankMN picture FrankMN · Jan 22, 2011 · Viewed 21.9k times · Source

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

casablanca picture casablanca · Jan 22, 2011

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?

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