I have following C++ code
A.h
namespace x {
namespace y {
namespace z {
struct Container;
class A
{
public:
A(Container& _container);
void info();
private:
Container& container;
};
}
}
}
A.cpp
#include "A.h"
#include <iostream>
namespace x {
namespace y {
namespace z {
A::A(Container& _container) : container(_container) {}
void A::info() {
std::cout << "Instance of A!" << std::endl;
}
}
}
}
Container.h
#include "A.h"
namespace x {
namespace y {
namespace z {
struct Container {
Container(): a(*this) {}
A a;
};
}
}
}
main.cpp
#include <cstdlib>
#include "Container.h"
int main(int argc, char** argv) {
x::y::z::Container container;
container.a.info();
return 0;
}
The above mentioned code is compilable and workable.
But let's say I move the Container.h out of the z namespace and let it in the y namespace (nested in the x namespace). So the code will look like that
A.h
namespace x {
namespace y {
namespace z {
struct Container;
class A
{
public:
A(x::y::Container& _container);
void info();
private:
x::y::Container& container;
};
}
}
}
A.cpp
#include "A.h"
#include <iostream>
namespace x {
namespace y {
namespace z {
A::A(x::y::Container& _container) : container(_container) {}
void A::info() {
std::cout << "Instance of A!" << std::endl;
}
}
}
}
Container.h
#include "A.h"
namespace x {
namespace y {
struct Container {
Container(): a(*this) {}
x::y::z::A a;
};
}
}
main.cpp
#include <cstdlib>
#include "Container.h"
int main(int argc, char** argv) {
x::y::Container container;
container.a.info();
return 0;
}
In that case the compilation fails with following error messages:
In file included from A.cpp:7:
A.h:26:22: error: expected ')' before '&' token
26 | A(x::y::Container& _container);
| ~ ^
| )
A.h:31:11: error: 'Container' in namespace 'x::y' does not name a type
31 | x::y::Container& container;
| ^~~~~~~~~
A.cpp:14:5: error: expected constructor, destructor, or type conversion before '(' token
14 | A::A(x::y::Container& _container) : container(_container)
| ^
Can anybody tell me why these error messages pop up in case I move the Container.h from the z namespace and let it in the y namespace nested in the x namespace?
The problem is that you never declared x::y::Container in A.h. You did declare x::y::z::Container, but that doesn't name the same type. Simply move the declaration into the y namespace:
namespace y { namespace z { struct Container;
Into ->
namespace y {
struct Container;
namespace z {