I have a program that works nicely with GCC, but compiling it with Clang instead makes the linker fail.
I think my issue is with template classes, so I implemented this small example.
test.cpp
:
#include "Point.h"
int main()
{
Point<int> p1;
Point<int> p2{ 3, 6 };
}
Point.h
:
#ifndef POINT_H
#define POINT_H
template<typename T>
class Point {
T x, y;
public:
Point();
Point(T, T);
};
template class Point<int>;
template class Point<float>;
#endif
Point.cpp
:
#include "Point.h"
template<typename T>
Point<T>::Point()
: x{0}, y{0}
{}
template<typename T>
Point<T>::Point(T t_x, T t_y)
: x{t_x}, y{t_y}
{}
When I build it with g++ Point.cpp test.cpp
, it works without a problem.
But with Clang, it gives the following errors:
$ clang++ Point.cpp test.cpp
/usr/bin/ld: /tmp/test-8ab886.o: in function `main':
test.cpp:(.text+0x1a): undefined reference to `Point<int>::Point()'
/usr/bin/ld: test.cpp:(.text+0x2d): undefined reference to `Point<int>::Point(int, int)'
clang-11: error: linker command failed with exit code 1 (use -v to see invocation)
Or, using lld:
$ clang++ -fuse-ld=lld Point.cpp test.cpp
ld.lld: error: undefined symbol: Point<int>::Point()
>>> referenced by test.cpp
>>> /tmp/test-f95759.o:(main)
ld.lld: error: undefined symbol: Point<int>::Point(int, int)
>>> referenced by test.cpp
>>> /tmp/test-f95759.o:(main)
clang-11: error: linker command failed with exit code 1 (use -v to see invocation)
I guess my explicit instantiations in Point.h
aren't good enough for Clang, but I can't figure what it wants.
Your explicit instantiation should be where definitions are visible, so at the end of Points.cpp
From class_template#Explicit_instantiation:
An explicit instantiation definition forces instantiation of the class, struct, or union they refer to. It may appear in the program anywhere after the template definition, and for a given argument-list, is only allowed to appear once in the entire program, no diagnostic required.