typedef and constructors

[timgj]

Hi there. I am in the process of attempting to learn C++ and have what I presume is an elementary problem, but I can't seem to find anything which solves it in either my copy of Stroustrup or online - possibly because I'm unsure what to search on.

As an exercise I have defined a class which will be used to hold angles. The angles will be held internally in Radians, but I want the ability to call a creator with angles in both Radians and Degrees. To this end I've stuck a couple of typedefs as below:

typedef double Radians;                                                         
typedef double Degrees;                                                         
                                                                                
class Angle                                                                     
{                                                                               
  static const double Pi = 3.1415926535897932385;                               
  Radians a;                                                                    
                                                                                
public:                                                                         
                                                                                
  Angle() {a = 0.0;};                                                           
  Angle(double d) {a = d;};                                                     
  Angle(Radians d){a = d;};                                                     
  Angle(Degrees d) {a = d * Pi/180.0;};                                         
  Angle(int d, int m, int s) {a = d + m/60.0 + s/3600.0;};                      
  Radians Get() {return a;};                                                    
};                                                                              

When I try compiling the code (g++ under Linux) I get:

[tim@tordella scratch]$ g++ -g3 -o angle2 angle2.cpp 
angle2.cpp:16: error: ‘Angle::Angle(Radians)’ cannot be overloaded
angle2.cpp:15: error: with ‘Angle::Angle(double)’
angle2.cpp:17: error: ‘Angle::Angle(Degrees)’ cannot be overloaded
angle2.cpp:15: error: with ‘Angle::Angle(double)’
[tim@tordella scratch]$ g++ -g3 -o angle2 angle2.cpp 
angle2.cpp:17: error: ‘Angle::Angle(Degrees)’ cannot be overloaded
angle2.cpp:16: error: with ‘Angle::Angle(Radians)’
[tim@tordella scratch]$ g++ -g3 -o angle2 angle2.cpp 
angle2.cpp:17: error: ‘Angle::Angle(Degrees)’ cannot be overloaded
angle2.cpp:16: error: with ‘Angle::Angle(Radians)’

I'm sure I'm making an elementary mistake. Can anyone shed any light on what I'm doing wrong.

Many thanks.

Tim.

[firix]

only static const integral data members can be initialized within a class

[timgj]

Apologies! I cut and pasted too much in the output box at the bottom. It should just have been...

[tim@tordella scratch]$ g++ -g3 -o angle2 angle2.cpp
angle2.cpp:17: error: ‘Angle::Angle(Degrees)’ cannot be overloaded
angle2.cpp:16: error: with ‘Angle::Angle(Radians)’

[firix]

class Angle
{
static double Pi;
Radians a;

public:

Angle() {a = 0.0;};
Angle(double d) {a = d;};
Angle(int d){a = d;};
Angle(float d) {a = d * Pi/180.0;};
Angle(int d, int m, int s) {a = d + m/60.0 + s/3600.0;};
Radians Get() {return a;};
};


only static const integral data members can be initialized within a class
member function already defined or declared.

[timgj]

"only static const integral data members can be initialized within a class
member function already defined or declared."

Indeed, thankyou. But if I remove the definition of Pi and replace it with the numeric value, I still get exactly the same error messages.

[firix]

typedef double Radians;
typedef double Degrees;

class Angle
{
static const double Pi;
Radians a;

public:
Angle() {a = 0.0;};
Angle(double d) {a = d;};
Angle(int d){a = d;};
Angle(float d) {a = d * Pi/180.0;};
Angle(int d, int m, int s) {a = d + m/60.0 + s/3600.0;};
Radians Get() {return a;};
};


const double Pi =3.1415926535897932385;
int main()
{




return 0;
}

[Galik]

The problem is that typedefs are not first class types. What I mean by that is that they are simply aliases for the underlying type. That means that you have 3 constructors with what the compiler sees as the same type: double.

You would have to make Radians and Degrees class types to achieve what you are after.