Thread: Classes and structures

Code:

typedef struct _VehicleInfo
{
	string make;
	string model;
} VehicleInfo;

//or else you have to declare it as:

struct VehicleInfo vinfo;

Originally posted by mcorn
Hello. I am having trouble accessing a structure from a class. I don't think I'm using the dot operator correctly. Could somebody help me with this issue? I've commented where the error occurs in the compiler. Thanks!

Code:

#include<iostream.h>
#include<string.h>

using namespace std;

struct VehicleInfo
{
	string make;
	string model;
};

class CVehicle
{
protected:

	VehicleInfo vinfo;
public:
	CVehicle(VehicleInfo);
	CVehicle(){};
	void getinfo();
	void writeinfo();
};


CVehicle::CVehicle(VehicleInfo info){vinfo=info;}

void CVehicle::getinfo()
{
	cout<<"\nEnter Make: ";
	cin>>vinfo.make;
	cout<<"\nEnter Model: ";
	cin>>vinfo.model;
}

void writeinfo(VehicleInfo vinfo)
{
    cout<<"\nMake is: " << vinfo.make <<"."
        <<"\nModel is: " << vinfo.model <<"." << endl;
}


int main()
{
         
CVehicle veh1(VehicleInfo info);  // the trouble is here somewhere

veh1.info.writeinfo(); //or here...I don't know what to do.	
//h1.getinfo();
//h1.writeinfo();

return 0;
}

<iostream.h> is depreciated, use <iostream>
<string.h> is depreciated and should be replaced with <cstring>, but that's not even your problem in this case -- you shouldnt have included <string.h> in the first place. the stl string class is in <string>

Originally posted by FillYourBrain

Code:

typedef struct _VehicleInfo
{
	string make;
	string model;
} VehicleInfo;

//or else you have to declare it as:

struct VehicleInfo vinfo;

Elad, this is why I said that. he will need "struct VehicleInfo" if he must use a struct.

Originally posted by FillYourBrain
Elad, this is why I said that. he will need "struct VehicleInfo" if he must use a struct.

No, that's in C, not C++

Originally posted by elad
don't typedef structs in C++, only in C.

There is no harm in providing the keyword 'struct', or 'class' for that matter. C++ allows you to leave it off. However, providing it does no harm. Additionally, using 'typedef' also does no harm. It's perfectly valid in C++ do typedef whatever you want. The same goes for #define.

The difference between C and C++ is that C++ allows you to omit the keyword. Providing it does no harm.

[edit]
I see you clarified yourself as I was typing. Exactly. It's optional, not required, but it does no harm if it's there.
[/edit]

Quzah.

You had a few problems.

Your writeinfo method was never defined -- you instead made a function called writeinfo and defined it.

You also weren't understanding passing arguments to your constructor -- you have to pass an instance of an object when it takes a parameter of an object, just like if it were an int you'd pass an int.

IE if a functions declaration is

void AFunc( int a );

you DONT call it by doing

AFunc( int a );

you'd call it like

AFunc( 3 );

or

AFunc( var ); // where var would be a variable of type int

// etc.

I gave 3 examples of constructing the object and using the methods and i fixed your method/function problem with writeinfo

Code:

#include<iostream>
#include<string>

using namespace std;

struct VehicleInfo
{
	string make;
	string model;
};

class CVehicle
{
protected:

	VehicleInfo vinfo;
public:
	CVehicle(VehicleInfo);
	CVehicle(){};
	void getinfo();
	void writeinfo();
};


CVehicle::CVehicle(VehicleInfo info){vinfo=info;}

void CVehicle::getinfo()
{
	cout<<"\nEnter Make: ";
	cin>>vinfo.make;
	cout<<"\nEnter Model: ";
	cin>>vinfo.model;
}

void CVehicle::writeinfo()
{
    cout<<"\nMake is: " << vinfo.make <<"."
        <<"\nModel is: " << vinfo.model <<"." << endl;
}


int main()
{
    CVehicle veh1;
    CVehicle veh2( VehicleInfo() );

    VehicleInfo InitialData;

    InitialData.make = "Blah";
    InitialData.model = "Poop";

    CVehicle veh3( InitialData );

    veh1.getinfo();
    veh1.writeinfo();

    veh2.getinfo();
    veh2.writeinfo();

    veh3.writeinfo();

    return 0;
}

Yup

Why would one use structures in a c++ program since classes are available ?

Why not? There's no real reason that they shouldn't. They can do exactly the same things.

Since both of them are the same thing, then why use structs sice classes are defined for C++ .I mean isnt classes a superior strct .Then why use it .I am a c programmer learning C++ so i just wanted to know if it does make any different.