problem with string&

[sernamar]

Hi,
I have the following base class

class UnitOfMeasure
{
public:
//...
std::string& GetName() {return _uomName;};
//...
protected:
std::string _uomName;
//...
};

And the subclass

class UomAngle : public UnitOfMeasure
{
public:
UomAngle();

UomAngle(const UnitOfMeasure &uom);

virtual ~UomAngle();

};

When I create an UomAngle object (called radian) and use it, all works
fine

cout<<radian->GetName();

Then, I have another base class

class Measure
{
public:
Measure();
virtual ~Measure();

double GetValue(){retu rn _value;};
std::string& GetUomName(){re turn _uom->GetName();};

protected:
double _value;
private:
UnitOfMeasure *_uom;
};

And the subclass

class Angle : public Measure
{
public:
Angle(double value,const std::string& uomName);

private:
UomAngle *_uom;
};

And I have the following problems:

1.- When I create an Angle and I want to get the uom name

Angle a1(180,degree);
cout<<a1.GetVal ue()<<"\t";
cout<<a1.GetUom Name();

it doesn't work. If I put the method

std::string& GetUomName(){re turn _uom->GetName();};

in the class Angle it works. But, why I have to do this? How can I do
it work without putting GetUomName in each subclass of Measure?

2.- The other problem is that

Angle a1(180,degree);
cout<<a1.GetVal ue()<<"\t";
cout<<a1.GetUom Name();

doesn't work because I have a problem with returning string&. I think
that I have a problem because in

std::string& GetUomName(){re turn _uom->GetName();};

_uom->GetName() works like a local variable, and I'm returning a
reference to this local variable.

Any idea to solve those problems or more problems that I could have?
Thanks!

[amparikh@gmail.com]

Re: problem with string&amp;


sernamar wrote:

Hi,
I have the following base class
>
class UnitOfMeasure
{
public:
//...
std::string& GetName() {return _uomName;};
//...
protected:
std::string _uomName;
//...
};
>
And the subclass
>
class UomAngle : public UnitOfMeasure
{
public:
UomAngle();
>
UomAngle(const UnitOfMeasure &uom);
>
virtual ~UomAngle();
>
};
>
When I create an UomAngle object (called radian) and use it, all works
fine
>
cout<<radian->GetName();
>
Then, I have another base class
>
class Measure
{
public:
Measure();
virtual ~Measure();
>
double GetValue(){retu rn _value;};
std::string& GetUomName(){re turn _uom->GetName();};
>
protected:
double _value;
private:
UnitOfMeasure *_uom;
};
>
And the subclass
>
class Angle : public Measure
{
public:
Angle(double value,const std::string& uomName);
>
private:
UomAngle *_uom;
};
>
And I have the following problems:
>
1.- When I create an Angle and I want to get the uom name
>
Angle a1(180,degree);
cout<<a1.GetVal ue()<<"\t";
cout<<a1.GetUom Name();
>
it doesn't work. If I put the method
>
std::string& GetUomName(){re turn _uom->GetName();};
>
in the class Angle it works. But, why I have to do this? How can I do
it work without putting GetUomName in each subclass of Measure?

Probably because you are not initializing the resp instance member
within Angle and Measure correctly ?
Both seemed to have a pointer named _uom and maybe that is messing up
stuff in your code(you have not posted all the code, so this is just a
guess).

>
2.- The other problem is that
>
Angle a1(180,degree);
cout<<a1.GetVal ue()<<"\t";
cout<<a1.GetUom Name();
>
doesn't work because I have a problem with returning string&. I think
that I have a problem because in
>
std::string& GetUomName(){re turn _uom->GetName();};
>
_uom->GetName() works like a local variable, and I'm returning a
reference to this local variable.
>
Any idea to solve those problems or more problems that I could have?
Thanks!

[Andre Kostur]

Re: problem with string&amp;

"sernamar" <sernamar@gmail .comwrote in news:1163628427 .605768.296020
@b28g2000cwb.go oglegroups.com:

Hi,
I have the following base class
>
class UnitOfMeasure
{
public:
//...
std::string& GetName() {return _uomName;};
//...
protected:
std::string _uomName;
//...
};
>
And the subclass
>
class UomAngle : public UnitOfMeasure
{
public:
UomAngle();
>
UomAngle(const UnitOfMeasure &uom);
>
virtual ~UomAngle();
>
};
>
When I create an UomAngle object (called radian) and use it, all works
fine
>
cout<<radian->GetName();
>
Then, I have another base class
>
class Measure
{
public:
Measure();
virtual ~Measure();
>
double GetValue(){retu rn _value;};
std::string& GetUomName(){re turn _uom->GetName();};
>
protected:
double _value;
private:
UnitOfMeasure *_uom;
};
>
And the subclass
>
class Angle : public Measure
{
public:
Angle(double value,const std::string& uomName);
>
private:
UomAngle *_uom;
};
>
And I have the following problems:
>
1.- When I create an Angle and I want to get the uom name
>
Angle a1(180,degree);
cout<<a1.GetVal ue()<<"\t";
cout<<a1.GetUom Name();
>
it doesn't work. If I put the method
>
std::string& GetUomName(){re turn _uom->GetName();};
>
in the class Angle it works. But, why I have to do this? How can I do
it work without putting GetUomName in each subclass of Measure?
>
2.- The other problem is that
>
Angle a1(180,degree);
cout<<a1.GetVal ue()<<"\t";
cout<<a1.GetUom Name();
>
doesn't work because I have a problem with returning string&. I think
that I have a problem because in
>
std::string& GetUomName(){re turn _uom->GetName();};
>
_uom->GetName() works like a local variable, and I'm returning a
reference to this local variable.
>
Any idea to solve those problems or more problems that I could have?
Thanks!
>
>

I don't see anywhere in there where _uom is ever pointing to anything
useful.

[sernamar]

Re: problem with string&amp;

Here is the full code:

// UnitOfMeasure.h
//
#include <string>

class UnitOfMeasure
{
public:
UnitOfMeasure() {};

UnitOfMeasure(s td::string &uomID,
std::string &uomName,
std::string &uomSymbol,
int measureType,
std::string &nameStandardUn it,
double scaleToStandard Unit,
double offsetToStandar dUnit,
std::string &formula);

virtual ~UnitOfMeasure( );

std::string& GetID() {return _uomID;};
std::string& GetName() {return _uomName;};
std::string& GetStandardName () {return _nameStandardUn it;};

std::string& GetSymbol() {return _uomSymbol;};

double ConvertToStanda rd(double value);
double ConvertFromStan dard(double value);

protected:
std::string _uomID;
std::string _uomName;
std::string _uomSymbol;
int _measureType;
std::string _nameStandardUn it;
double _scaleToStandar dUnit;
double _offsetToStanda rdUnit;
std::string _formula;
};

// UnitOfMeasure.c pp
//
#include "UnitOfMeasure. h"

using namespace std;

UnitOfMeasure:: UnitOfMeasure (std::string &uomID,
std::string &uomName,
std::string &uomSymbol,
int measureType,
std::string &nameStandardUn it,
double scaleToStandard Unit,
double offsetToStandar dUnit,
std::string &formula):
_uomID(uomID),
_uomName(uomNam e),
_uomSymbol(uomS ymbol),
_measureType(me asureType),
_nameStandardUn it(nameStandard Unit),
_scaleToStandar dUnit(scaleToSt andardUnit),
_offsetToStanda rdUnit(offsetTo StandardUnit),
_formula(formul a)
{
}

UnitOfMeasure:: ~UnitOfMeasure( )
{
}

double UnitOfMeasure:: ConvertToStanda rd(double value)
{
return value * _scaleToStandar dUnit + _offsetToStanda rdUnit;
}

double UnitOfMeasure:: ConvertFromStan dard(double value)
{
return (value - _offsetToStanda rdUnit) / _scaleToStandar dUnit;
}

// UomAngle.h
//
class UomAngle : public UnitOfMeasure
{
public:
UomAngle();

UomAngle(const UnitOfMeasure &uom);

virtual ~UomAngle();

};

// UomAngle.cpp
//
#include "UomAngle.h "

UomAngle::UomAn gle():UnitOfMea sure()
{
}

UomAngle::UomAn gle(const UnitOfMeasure &uom):UnitOfMea sure(uom)
{
}

UomAngle::~UomA ngle()
{
}

// Measure.h
//
#include <string>
#include "UnitOfMeasure. h"

class Measure
{
public:
Measure();

virtual ~Measure();

double GetValue(){retu rn _value;};
std::string& GetUomName(){re turn _uom->GetName();};
std::string& GetUomSymbol() {return _uom->GetSymbol(); };

protected:
double _value;
private:
UnitOfMeasure *_uom;
};

// Measure.cpp
//
#include "Measure.h"

Measure::Measur e()
{
}

Measure::~Measu re()
{
}

// Angle.h
//
#include "Measure.h"
#include "UomAngle.h "

class Angle : public Measure
{
public:
Angle();

Angle(double value,const std::string& uomName);

virtual ~Angle();

std::string& GetUomName(){re turn _uom->GetName();};
std::string& GetUomSymbol() {return _uom->GetSymbol(); };

Angle ConvertToStanda rd();
Angle ConvertFromStan dard(const std::string& uomName);
Angle ConvertTo(const std::string& uomName);

private:
UomAngle *_uom;
Angle(double value,UomAngle* uom);
};

// Angle.cpp
//
#include "Angle.h"
#include "UomManager .h"

using namespace std;

Angle::Angle()
{
}

Angle::Angle(do uble value,const string &uomName)
{
_value = value;
UomManager *uomMng = UomManager::Get Instance();
_uom = uomMng->GetUomAngle(uo mName);
}

Angle::Angle(do uble value,UomAngle* uom)
{
_value = value;
_uom = uom;
}

Angle::~Angle()
{
}

Angle Angle::ConvertT oStandard()
{
string stdname(_uom->GetStandardNam e());
if (_uom->GetName() == stdname) return *this;
else {
UomManager *uomMng = UomManager::Get Instance();
UomAngle *stduom = uomMng ->GetUomAngle(st dname);
double newvalue = _uom->ConvertToStand ard(_value);
return Angle(newvalue, stduom);
}
}

Angle Angle::ConvertF romStandard(con st std::string& uomName)
{
if (_uom->GetName() == uomName) return *this;
else {
UomManager *uomMng = UomManager::Get Instance();
UomAngle *uom = uomMng ->GetUomAngle(uo mName);
double newvalue = uom->ConvertFromSta ndard(_value);
return Angle(newvalue, uom);
}
}

Angle Angle::ConvertT o(const std::string& uomName)
{
if (_uom->GetName() == uomName) return *this;
else {
UomManager *uomMng = UomManager::Get Instance();
UomAngle *uom = uomMng ->GetUomAngle(uo mName);
double stdvalue = _uom->ConvertToStand ard(_value);
double newvalue = uom->ConvertFromSta ndard(stdvalue) ;
return Angle(newvalue, uom);
}
}


note: UomManager is a unit of measure manager that allows to get a
pointer to a UomAngle with the method GetUomAngle(uom Name), where
uomName is a string.

//main.cpp
//
#include <cstdlib>
#include <iostream>
#include <iomanip>

#include <uommanager.h >
#include <angle.h>

using namespace std;

int main(int argc, char *argv[])
{
string degree("degree" );

Angle a1(180,degree);
cout<<a1.GetVal ue()<<"\t";
cout<<a1.GetUom Symbol();
cout<<" ("<<a1.GetUomNa me()<<")"<<endl <<endl;

system("pause") ;
return EXIT_SUCCESS;
}

That's all. If you need something more, just tell me.
Thanks