Constructor problem

[Chiller]

I am in the process of writing a class that will represent metric distances
by accepting a value (ie, 3) and a unit of measure (ie, m).

I've written my constructor in the .h file as

Distance (int, char);

I've written the constructor in the .cpp implementation file as:

Distance :: Distance ( int n, char m) : nu(n), me(m) {}

When I try to enter a value in main using:
Distance a = Distance (5, m);

I get an error saying the value "m" is undeclared, yet the 5 is accepted.
Considering I declared these variables in the initial constructor I can't
understand why I'm getting this error.

I'd appreciate it if someone could give me an explanation of what I'm doing
wrong and how I can correct my mistake.

Thanks

[David Harmon]

Re: Constructor problem

On Sat, 10 Apr 2004 03:43:59 GMT in comp.lang.c++, "Chiller" <...@...>
wrote,[color=blue]
>Distance (int, char);[/color]
[color=blue]
>Distance a = Distance (5, m);
>
>I get an error saying the value "m" is undeclared,[/color]

It is undeclared. m is a identifier, not a char literal as 'm' would
be.

[David Harmon]

Re: Constructor problem

On Sat, 10 Apr 2004 03:43:59 GMT in comp.lang.c++, "Chiller" <...@...>
wrote,[color=blue]
>Distance (int, char);[/color]
[color=blue]
>Distance a = Distance (5, m);
>
>I get an error saying the value "m" is undeclared,[/color]

It is undeclared. m is a identifier, not a char literal as 'm' would
be.

[Thomas Tutone]

Re: Constructor problem

"Chiller" <...@...> wrote in message
news:3d1a35a44a 40e3806950ba940 252df12@news.te ranews.com...
[color=blue]
> I am in the process of writing a class that will represent metric[/color]
distances[color=blue]
> by accepting a value (ie, 3) and a unit of measure (ie, m).
>
> I've written my constructor in the .h file as
>
> Distance (int, char);
>
> I've written the constructor in the .cpp implementation file as:
>
> Distance :: Distance ( int n, char m) : nu(n), me(m) {}
>
> When I try to enter a value in main using:
> Distance a = Distance (5, m);
>
> I get an error saying the value "m" is undeclared, yet the 5 is accepted.
> Considering I declared these variables in the initial constructor I can't
> understand why I'm getting this error.
>
> I'd appreciate it if someone could give me an explanation of what I'm[/color]
doing[color=blue]
> wrong and how I can correct my mistake.[/color]

If you mean the literal character 'm', then you can do:

Distance a = Distance(5, 'm');

or, more concisely:

Distance a(5, 'm');

If you don't mean the literal character 'm', then you need to be more
specific about what it is you are trying to do. In particular, provide an
actual compilable piece of code - what you provided is not compilable as is.

Best regards,

Tom

[Thomas Tutone]

Re: Constructor problem

"Chiller" <...@...> wrote in message
news:3d1a35a44a 40e3806950ba940 252df12@news.te ranews.com...
[color=blue]
> I am in the process of writing a class that will represent metric[/color]
distances[color=blue]
> by accepting a value (ie, 3) and a unit of measure (ie, m).
>
> I've written my constructor in the .h file as
>
> Distance (int, char);
>
> I've written the constructor in the .cpp implementation file as:
>
> Distance :: Distance ( int n, char m) : nu(n), me(m) {}
>
> When I try to enter a value in main using:
> Distance a = Distance (5, m);
>
> I get an error saying the value "m" is undeclared, yet the 5 is accepted.
> Considering I declared these variables in the initial constructor I can't
> understand why I'm getting this error.
>
> I'd appreciate it if someone could give me an explanation of what I'm[/color]
doing[color=blue]
> wrong and how I can correct my mistake.[/color]

If you mean the literal character 'm', then you can do:

Distance a = Distance(5, 'm');

or, more concisely:

Distance a(5, 'm');

If you don't mean the literal character 'm', then you need to be more
specific about what it is you are trying to do. In particular, provide an
actual compilable piece of code - what you provided is not compilable as is.

Best regards,

Tom

[Chiller]

Re: Constructor problem

Is there a way that I can write the constructor so that it will simply
accept two variables, ie. when I create an object I can do so by simply
typing

Distance a = Distance (5, m); or
Distance a = Distance (5, km); etc

without having to use ' ' or declaring m, km?

Thanks

[Chiller]

Re: Constructor problem

Is there a way that I can write the constructor so that it will simply
accept two variables, ie. when I create an object I can do so by simply
typing

Distance a = Distance (5, m); or
Distance a = Distance (5, km); etc

without having to use ' ' or declaring m, km?

Thanks

[Mark A. Gibbs]

Re: Constructor problem

Chiller wrote:
[color=blue]
> Is there a way that I can write the constructor so that it will simply
> accept two variables, ie. when I create an object I can do so by simply
> typing
>
> Distance a = Distance (5, m); or
> Distance a = Distance (5, km); etc
>
> without having to use ' ' or declaring m, km?[/color]

yes, but really, i'm still not sure what exactly you're looking for.

it *sounds* like you want to do something more like this:

class DistanceUnit
{
private:
DistanceUnit(in t value) :
v_(value),
n_(name)
{}

DistanceUnit(Di stanceUnit const&);
void operator=(Dista nceUnit const&);

int v_;

friend class Distance;
};

class Distance
{
public:
static const DistanceUnit m;
static const DistanceUnit km;

Distance(int n, const DistanceUnit& unit) :
value_(n),
unit_(unit)
{}

private:
int value_;
DistanceUnit unit_;
};

Distance::Dista nceUnit m(1);
Distance::Dista nceUnit km(1000);

to use:

using Distance::m;
Distance a(5, m);

or:

Distance a(5, Distance::m);

this is just a *very* rough starting point - i wrote this off the cuff
without even checking anything (maybe you should put DistanceUnit in
Distance - that's up to you). unless you're willing to supply more
information, i can't offer you any more than this. but starting from
here you can create a system that can handle arbitrary distance units in
meters, kilometers, millimeters, inches, feet, nautical miles or cubits
(though you'd have to give up on the ints and go to floats at least),
can convert automatically between any two of them and (if you're clever
enough to add a string to DistanceUnit) print out the length in the
given unit (or any other chosen unit).

mark

[Mark A. Gibbs]

Re: Constructor problem

Chiller wrote:
[color=blue]
> Is there a way that I can write the constructor so that it will simply
> accept two variables, ie. when I create an object I can do so by simply
> typing
>
> Distance a = Distance (5, m); or
> Distance a = Distance (5, km); etc
>
> without having to use ' ' or declaring m, km?[/color]

yes, but really, i'm still not sure what exactly you're looking for.

it *sounds* like you want to do something more like this:

class DistanceUnit
{
private:
DistanceUnit(in t value) :
v_(value),
n_(name)
{}

DistanceUnit(Di stanceUnit const&);
void operator=(Dista nceUnit const&);

int v_;

friend class Distance;
};

class Distance
{
public:
static const DistanceUnit m;
static const DistanceUnit km;

Distance(int n, const DistanceUnit& unit) :
value_(n),
unit_(unit)
{}

private:
int value_;
DistanceUnit unit_;
};

Distance::Dista nceUnit m(1);
Distance::Dista nceUnit km(1000);

to use:

using Distance::m;
Distance a(5, m);

or:

Distance a(5, Distance::m);

this is just a *very* rough starting point - i wrote this off the cuff
without even checking anything (maybe you should put DistanceUnit in
Distance - that's up to you). unless you're willing to supply more
information, i can't offer you any more than this. but starting from
here you can create a system that can handle arbitrary distance units in
meters, kilometers, millimeters, inches, feet, nautical miles or cubits
(though you'd have to give up on the ints and go to floats at least),
can convert automatically between any two of them and (if you're clever
enough to add a string to DistanceUnit) print out the length in the
given unit (or any other chosen unit).

mark

[Chiller]

Re: Constructor problem

Below I have included the .h file .cpp implementation file. The .cpp file
has a TEST_DISTANCE driver that needs to be declared to the preprocessor to
allow it to be compiled.

I'd greatly appreciate some advice on what I'm doing wrong and how I can
correct the problem.

Whenever I compile I get the following errors:

Distance.cpp(32 ) : error C2556: 'char Distance::measu re(void) const' :
overloaded function differs only by return type from 'int
Distance::measu re(void) const'

Distance.h(25) : see declaration of 'Distance::meas ure'

Distance.cpp(32 ) : error C2371: 'Distance::meas ure' : redefinition;
different basic types

Distance.h(25) : see declaration of 'Distance::meas ure'

Distance.cpp(39 ) : error C2264: 'Distance::meas ure' : error in function
definition or declaration; function not called



..h file as follows

*************** *************** *************** *****

#ifndef DISTANCE_H

#define DISTANCE_H

#include <iostream>

using namespace std;

class Distance

{

public :

Distance (int, char) ; // constructor - takes int and char values

Distance (int) ; // constructor - takes int value

Distance (void) ; // default - zero

//access member functions

int number (void) const;

int measure (void) const;


private :

int nu ; // the value

char me ; // the unit of measure (m)

} ;

// provide an overload of "<<" for easy display

ostream& operator<< (ostream&, const Distance&);

#endif



..cpp file as follows

*************** *************** ***********

#include "Distance.h "

#include <iostream>

#include <string>

using namespace std;

/*-------------------------------------------------------*\

| implementation of member functions |

\*-------------------------------------------------------*/

// constructor

Distance :: Distance (int n, char m) : nu(n), me(m) {}

Distance :: Distance (int n) : nu(n) {}

Distance :: Distance (void) : nu(0) {}

// access functions

int Distance :: number (void) const

{

return nu;

}

char Distance :: measure (void) const

{

return me;

}

// provide an overload of "<<" for easy display

ostream& operator<< (ostream& out, const Distance& d)

{

out << "(" << d.number() << "," << d.measure() << ")" ;

return out;

}

/*-------------------------------------------------------*\

| test driver for the Distance class |

\*-------------------------------------------------------*/

#ifdef TEST_DISTANCE // .... Distance class .... test driver

int main (void)

{

// create test input

Distance a = Distance (6);

Distance b (4);

Distance c (2);

Distance d;

Distance e (5, 'm');


cout << a << endl << b << endl << c << endl << d << endl << e << endl;



cin.ignore();

return 0; // normal termination

}

#endif

[Chiller]

Re: Constructor problem

Below I have included the .h file .cpp implementation file. The .cpp file
has a TEST_DISTANCE driver that needs to be declared to the preprocessor to
allow it to be compiled.

I'd greatly appreciate some advice on what I'm doing wrong and how I can
correct the problem.

Whenever I compile I get the following errors:

Distance.cpp(32 ) : error C2556: 'char Distance::measu re(void) const' :
overloaded function differs only by return type from 'int
Distance::measu re(void) const'

Distance.h(25) : see declaration of 'Distance::meas ure'

Distance.cpp(32 ) : error C2371: 'Distance::meas ure' : redefinition;
different basic types

Distance.h(25) : see declaration of 'Distance::meas ure'

Distance.cpp(39 ) : error C2264: 'Distance::meas ure' : error in function
definition or declaration; function not called



..h file as follows

*************** *************** *************** *****

#ifndef DISTANCE_H

#define DISTANCE_H

#include <iostream>

using namespace std;

class Distance

{

public :

Distance (int, char) ; // constructor - takes int and char values

Distance (int) ; // constructor - takes int value

Distance (void) ; // default - zero

//access member functions

int number (void) const;

int measure (void) const;


private :

int nu ; // the value

char me ; // the unit of measure (m)

} ;

// provide an overload of "<<" for easy display

ostream& operator<< (ostream&, const Distance&);

#endif



..cpp file as follows

*************** *************** ***********

#include "Distance.h "

#include <iostream>

#include <string>

using namespace std;

/*-------------------------------------------------------*\

| implementation of member functions |

\*-------------------------------------------------------*/

// constructor

Distance :: Distance (int n, char m) : nu(n), me(m) {}

Distance :: Distance (int n) : nu(n) {}

Distance :: Distance (void) : nu(0) {}

// access functions

int Distance :: number (void) const

{

return nu;

}

char Distance :: measure (void) const

{

return me;

}

// provide an overload of "<<" for easy display

ostream& operator<< (ostream& out, const Distance& d)

{

out << "(" << d.number() << "," << d.measure() << ")" ;

return out;

}

/*-------------------------------------------------------*\

| test driver for the Distance class |

\*-------------------------------------------------------*/

#ifdef TEST_DISTANCE // .... Distance class .... test driver

int main (void)

{

// create test input

Distance a = Distance (6);

Distance b (4);

Distance c (2);

Distance d;

Distance e (5, 'm');


cout << a << endl << b << endl << c << endl << d << endl << e << endl;



cin.ignore();

return 0; // normal termination

}

#endif

[John Harrison]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:59b0c5bce8 57990952dc322b6 a1458b2@news.te ranews.com...[color=blue]
> Is there a way that I can write the constructor so that it will simply
> accept two variables, ie. when I create an object I can do so by simply
> typing
>
> Distance a = Distance (5, m); or
> Distance a = Distance (5, km); etc
>[/color]

Its more common to write

Distance a(5, m);
Distance a(5, km);
[color=blue]
> without having to use ' ' or declaring m, km?
>
> Thanks
>[/color]

Probably what you want is an enum

enum
{
m,
km,
miles,
};

etc.

Put that at the top of you program and then change char to int. I.e. you
constructor becomes

Distance (int, int);

But I'd seriously consider using longer names than m, km etc. How about

enum
{
units_meters,
units_kilometer s,
units_miles,
};

that's how it is normally done.

john

[John Harrison]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:59b0c5bce8 57990952dc322b6 a1458b2@news.te ranews.com...[color=blue]
> Is there a way that I can write the constructor so that it will simply
> accept two variables, ie. when I create an object I can do so by simply
> typing
>
> Distance a = Distance (5, m); or
> Distance a = Distance (5, km); etc
>[/color]

Its more common to write

Distance a(5, m);
Distance a(5, km);
[color=blue]
> without having to use ' ' or declaring m, km?
>
> Thanks
>[/color]

Probably what you want is an enum

enum
{
m,
km,
miles,
};

etc.

Put that at the top of you program and then change char to int. I.e. you
constructor becomes

Distance (int, int);

But I'd seriously consider using longer names than m, km etc. How about

enum
{
units_meters,
units_kilometer s,
units_miles,
};

that's how it is normally done.

john

[John Harrison]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:2f1429a771 8931f84a0463892 99dff75@news.te ranews.com...[color=blue]
> Below I have included the .h file .cpp implementation file. The .cpp file
> has a TEST_DISTANCE driver that needs to be declared to the preprocessor[/color]
to[color=blue]
> allow it to be compiled.
>
> I'd greatly appreciate some advice on what I'm doing wrong and how I can
> correct the problem.
>
> Whenever I compile I get the following errors:
>
> Distance.cpp(32 ) : error C2556: 'char Distance::measu re(void) const' :
> overloaded function differs only by return type from 'int
> Distance::measu re(void) const'
>[/color]

[snip]
[color=blue]
> int measure (void) const;[/color]

You declare measure as returning an int here

[snip][color=blue]
>
> char Distance :: measure (void) const[/color]

But you define measure and returning a char here. The definition and
dclaration must be the same.

john

[John Harrison]

Re: Constructor problem


"Chiller" <...@...> wrote in message
news:2f1429a771 8931f84a0463892 99dff75@news.te ranews.com...[color=blue]
> Below I have included the .h file .cpp implementation file. The .cpp file
> has a TEST_DISTANCE driver that needs to be declared to the preprocessor[/color]
to[color=blue]
> allow it to be compiled.
>
> I'd greatly appreciate some advice on what I'm doing wrong and how I can
> correct the problem.
>
> Whenever I compile I get the following errors:
>
> Distance.cpp(32 ) : error C2556: 'char Distance::measu re(void) const' :
> overloaded function differs only by return type from 'int
> Distance::measu re(void) const'
>[/color]

[snip]
[color=blue]
> int measure (void) const;[/color]

You declare measure as returning an int here

[snip][color=blue]
>
> char Distance :: measure (void) const[/color]

But you define measure and returning a char here. The definition and
dclaration must be the same.

john