C++ How to Reference Other Classes? - c++

Question

I'm new to C++, and I'm having some trouble setting up a simple class reference.
Class: Test.hh
#ifndef _TEST_HH_
#define _TEST_HH_
class Test {
public:
Test (double x);
};
#endif
Class Test.cc
#include "Test.hh"
#include <stdio.h>
Test::Test(double x) {
printf("%f",x);
}
Now I want to access this class from another class:
Class: DriverClass.hh
#ifndef _DRIVERCLASS_HH_
#define _DRIVERCLASS_HH_
#include "Test.hh"
class DriverClass {
public:
DriverClass(double y);
Test *t;
}
#endif
Class DriverClass.cc
#include "DriverClass.hh"
DriverClass::DriverClass(double y) {
t = new Test(y);
}
However, I get an error: "undefined reference to 'Test::Test(double)?
Does anyone know what might be wrong? Please assume that DriverClass is being called directly from a main method (not shown).

Answer 1

There is still an error in your post - a missing ; after the DriverClass
declaration. The rest is correct.
You should compile and link all the sources. The following is a sample Makefile and a
sample test code.
Makefile
all: t
t: t.cc DriverClass.cc Test.cc
g++ -Wall -g -o $# $^
clean:
rm -f *.o t
However, note that it's generally recommended to compile the sources into objects separately in order to compile only the sources changed after the last compilation. For example:
CFLAGS=-Wall -g
all: t
t: t.o DriverClass.o Test.o
g++ -o $# $^
t.o: t.cc DriverClass.o Test.o
g++ $(CFLAGS) -c $< -o $#
DriverClass.o: DriverClass.cc
g++ $(CFLAGS) -c $< -o $#
Test.o: Test.cc
g++ $(CFLAGS) -c $^ -o $#
clean:
rm -f *.o t
I've used the GNU compiler. For the meaning of $# and $^ variables refer to the official documentation.
t.cc
#include "Test.hh"
#include "DriverClass.hh"
int main(int argc, char const* argv[])
{
DriverClass d(10.4);
return 0;
}
Testing
$ make
g++ -Wall -g -o t t.cc DriverClass.cc Test.cc
$ ./t
10.400000
P.S.: don't forget to delete the allocated object.