Trouble with constructor

[San]

Hi,

I wrote two simple constructors (one of them default) to initialize a
student object.
Student::Studen t(string name)
{
student_name = name;
student_id = LATEST_ID + 1;
student_address ("");
student_phone(0 );
student_email(" ");

}
Student::Studen t()
{
student_name("" );
student_id = LATEST_ID + 1;
student_address ("");
student_phone(0 );
student_email(" ");
}

When I try to use the following:
Student stud_1("San");
The g++ compiler gives an error message "undefined message to
Student::Studen t(basic_string( char, string_char_tra its(char),
_default_alloc_ template(0,0))) "

The compiler has no problem if I use Student stud_1();

Is the trouble due to the fact that I am trying to assign a string and
that there is no copy constructor defined?

Any help would be greatly appreciated.

Thanks,
San

[Leor Zolman]

Re: Trouble with constructor

On 9 Apr 2004 12:37:58 -0700, abc_99_420@hotm ail.com (San) wrote:
[color=blue]
>Hi,
>
>I wrote two simple constructors (one of them default) to initialize a
>student object.
>Student::Stude nt(string name)
> {
> student_name = name;
> student_id = LATEST_ID + 1;
> student_address ("");[/color]
You've confused member initializer syntax with stuff you do elsewhere than
in the initializer list. You want something like this:

Student::Studen t(string name) : student_name(na me),
student_id(LATE ST_ID + 1), student_phone(0 ) {}

and just leave the others out (assuming their default constructor behaves
the same as their constructor taking "")

Note that the only place member objects can be /initialized/ by a
constructor is in that constructor's initializer list; otherwise, if you
leave the job until you're within the body of the constructor, you're stuck
with having to do an /assignment/ (and the objects you're assigning to will
already have had their default constructors run on them, whether you like
it or not.)
-leor

[color=blue]
> student_phone(0 );
> student_email(" ");
>
> }
>Student::Stude nt()
> {
> student_name("" );
> student_id = LATEST_ID + 1;
> student_address ("");
> student_phone(0 );
> student_email(" ");
> }
>
>When I try to use the following:
>Student stud_1("San");
>The g++ compiler gives an error message "undefined message to
>Student::Stude nt(basic_string (char, string_char_tra its(char),
>_default_alloc _template(0,0)) )"
>
>The compiler has no problem if I use Student stud_1();
>
>Is the trouble due to the fact that I am trying to assign a string and
>that there is no copy constructor defined?
>
>Any help would be greatly appreciated.
>
>Thanks,
>San[/color]

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:

https://www.bdsoft.com/tools/stlfilt.html

[Leor Zolman]

Re: Trouble with constructor

On 9 Apr 2004 12:37:58 -0700, abc_99_420@hotm ail.com (San) wrote:
[color=blue]
>Hi,
>
>I wrote two simple constructors (one of them default) to initialize a
>student object.
>Student::Stude nt(string name)
> {
> student_name = name;
> student_id = LATEST_ID + 1;
> student_address ("");[/color]
You've confused member initializer syntax with stuff you do elsewhere than
in the initializer list. You want something like this:

Student::Studen t(string name) : student_name(na me),
student_id(LATE ST_ID + 1), student_phone(0 ) {}

and just leave the others out (assuming their default constructor behaves
the same as their constructor taking "")

Note that the only place member objects can be /initialized/ by a
constructor is in that constructor's initializer list; otherwise, if you
leave the job until you're within the body of the constructor, you're stuck
with having to do an /assignment/ (and the objects you're assigning to will
already have had their default constructors run on them, whether you like
it or not.)
-leor

[color=blue]
> student_phone(0 );
> student_email(" ");
>
> }
>Student::Stude nt()
> {
> student_name("" );
> student_id = LATEST_ID + 1;
> student_address ("");
> student_phone(0 );
> student_email(" ");
> }
>
>When I try to use the following:
>Student stud_1("San");
>The g++ compiler gives an error message "undefined message to
>Student::Stude nt(basic_string (char, string_char_tra its(char),
>_default_alloc _template(0,0)) )"
>
>The compiler has no problem if I use Student stud_1();
>
>Is the trouble due to the fact that I am trying to assign a string and
>that there is no copy constructor defined?
>
>Any help would be greatly appreciated.
>
>Thanks,
>San[/color]

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:

https://www.bdsoft.com/tools/stlfilt.html

[John Carson]

Re: Trouble with constructor

"San" <abc_99_420@hot mail.com> wrote in message
news:ba6b3627.0 404091137.6e971 f65@posting.goo gle.com[color=blue]
> Hi,
>
> I wrote two simple constructors (one of them default) to initialize a
> student object.
> Student::Studen t(string name)
> {
> student_name = name;
> student_id = LATEST_ID + 1;
> student_address ("");
> student_phone(0 );
> student_email(" ");
>
> }
> Student::Studen t()
> {
> student_name("" );
> student_id = LATEST_ID + 1;
> student_address ("");
> student_phone(0 );
> student_email(" ");
> }
>
> When I try to use the following:
> Student stud_1("San");
> The g++ compiler gives an error message "undefined message to
> Student::Studen t(basic_string( char, string_char_tra its(char),
> _default_alloc_ template(0,0))) "
>
> The compiler has no problem if I use Student stud_1();
>
> Is the trouble due to the fact that I am trying to assign a string and
> that there is no copy constructor defined?
>
> Any help would be greatly appreciated.
>
> Thanks,
> San[/color]

Unless g++ supports all sorts of non-standard nonsense, neither of your
constructors can compile. You can't make assignments with calls like

student_name("" );

or

student_phone(0 );

Show us the real code and we may have some chance of identifying the
problem.

Incidentally,

Student stud_1();

does not define a Student object and invoke the default constructor.
Rather, it
declares a function called stud_1 that takes no arguments and returns a
Student object. To define a Student object, drop the brackets, i.e., use

Student stud_1;

--
John Carson
1. To reply to email address, remove donald
2. Don't reply to email address (post here instead)

[John Carson]

Re: Trouble with constructor

"San" <abc_99_420@hot mail.com> wrote in message
news:ba6b3627.0 404091137.6e971 f65@posting.goo gle.com[color=blue]
> Hi,
>
> I wrote two simple constructors (one of them default) to initialize a
> student object.
> Student::Studen t(string name)
> {
> student_name = name;
> student_id = LATEST_ID + 1;
> student_address ("");
> student_phone(0 );
> student_email(" ");
>
> }
> Student::Studen t()
> {
> student_name("" );
> student_id = LATEST_ID + 1;
> student_address ("");
> student_phone(0 );
> student_email(" ");
> }
>
> When I try to use the following:
> Student stud_1("San");
> The g++ compiler gives an error message "undefined message to
> Student::Studen t(basic_string( char, string_char_tra its(char),
> _default_alloc_ template(0,0))) "
>
> The compiler has no problem if I use Student stud_1();
>
> Is the trouble due to the fact that I am trying to assign a string and
> that there is no copy constructor defined?
>
> Any help would be greatly appreciated.
>
> Thanks,
> San[/color]

Unless g++ supports all sorts of non-standard nonsense, neither of your
constructors can compile. You can't make assignments with calls like

student_name("" );

or

student_phone(0 );

Show us the real code and we may have some chance of identifying the
problem.

Incidentally,

Student stud_1();

does not define a Student object and invoke the default constructor.
Rather, it
declares a function called stud_1 that takes no arguments and returns a
Student object. To define a Student object, drop the brackets, i.e., use

Student stud_1;

--
John Carson
1. To reply to email address, remove donald
2. Don't reply to email address (post here instead)

[Mike Higginbottom]

Re: Trouble with constructor

On 9 Apr 2004 12:37:58 -0700, San <abc_99_420@hot mail.com> wrote:
[color=blue]
> I wrote two simple constructors (one of them default) to initialize a
> student object.[/color]

[snip]
[color=blue]
> When I try to use the following:
> Student stud_1("San");
> The g++ compiler gives an error message "undefined message to
> Student::Studen t(basic_string( char, string_char_tra its(char),
> _default_alloc_ template(0,0))) "
>[/color]

It would be nice to see the class declaration but the following works fine
on .NET:

class Student
{
public:
Student();
Student(std::st ring name);
private:
std::string student_name;
};

Student::Studen t(std::string name)
{
student_name = name;
}

Student::Studen t()
{
student_name = ""; //Note: this is not student_name("" )
}

Student stud_1("San");
[color=blue]
> The compiler has no problem if I use Student stud_1();
>[/color]
I'd expect it to fail on:

student_name("" );
[color=blue]
> Is the trouble due to the fact that I am trying to assign a string and
> that there is no copy constructor defined?[/color]
No. The default copy ctor will work fine for this class and will just
call the copy ctor for std::string which does exist.
[color=blue]
>
> Any help would be greatly appreciated.
>[/color]
A better (more efficient) way would be to use initialization rather than
assignment (see [1] or Scott Meyers' Effective C++)in the two ctors you
define, as follows:

Student::Studen t(std::string name) : student_name(na me)
{
}

which may have been what you were trying to do inthe first place.

[1] http://www.parashift.com/c++-faq-lit....html#faq-10.6

--
Mike Higginbottom

http://www.peak41.co.uk

[Mike Higginbottom]

Re: Trouble with constructor

On 9 Apr 2004 12:37:58 -0700, San <abc_99_420@hot mail.com> wrote:
[color=blue]
> I wrote two simple constructors (one of them default) to initialize a
> student object.[/color]

[snip]
[color=blue]
> When I try to use the following:
> Student stud_1("San");
> The g++ compiler gives an error message "undefined message to
> Student::Studen t(basic_string( char, string_char_tra its(char),
> _default_alloc_ template(0,0))) "
>[/color]

It would be nice to see the class declaration but the following works fine
on .NET:

class Student
{
public:
Student();
Student(std::st ring name);
private:
std::string student_name;
};

Student::Studen t(std::string name)
{
student_name = name;
}

Student::Studen t()
{
student_name = ""; //Note: this is not student_name("" )
}

Student stud_1("San");
[color=blue]
> The compiler has no problem if I use Student stud_1();
>[/color]
I'd expect it to fail on:

student_name("" );
[color=blue]
> Is the trouble due to the fact that I am trying to assign a string and
> that there is no copy constructor defined?[/color]
No. The default copy ctor will work fine for this class and will just
call the copy ctor for std::string which does exist.
[color=blue]
>
> Any help would be greatly appreciated.
>[/color]
A better (more efficient) way would be to use initialization rather than
assignment (see [1] or Scott Meyers' Effective C++)in the two ctors you
define, as follows:

Student::Studen t(std::string name) : student_name(na me)
{
}

which may have been what you were trying to do inthe first place.

[1] http://www.parashift.com/c++-faq-lit....html#faq-10.6

--
Mike Higginbottom

http://www.peak41.co.uk

[Leor Zolman]

Re: Trouble with constructor

On Sat, 10 Apr 2004 06:17:33 +1000, "John Carson"
<donaldquixote@ datafast.net.au > wrote:
[color=blue]
>
>Incidentally ,
>
>Student stud_1();
>
>does not define a Student object and invoke the default constructor.
>Rather, it
>declares a function called stud_1 that takes no arguments and returns a
>Student object. To define a Student object, drop the brackets, i.e., use
>
>Student stud_1;[/color]

Good catch. I missed it (but I must admit I wasn't looking all that hard
any more by the time I reached that section of the post).

Ironically, this is the very item I contributed to Bruce Eckel & Chuck
Allison's "C++ Annoyances" session at SD West recently. The reason it
annoys me should now be quite apparent: I don't /notice/ it ;-)
-leor


--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:

https://www.bdsoft.com/tools/stlfilt.html

[Leor Zolman]

Re: Trouble with constructor

On Sat, 10 Apr 2004 06:17:33 +1000, "John Carson"
<donaldquixote@ datafast.net.au > wrote:
[color=blue]
>
>Incidentally ,
>
>Student stud_1();
>
>does not define a Student object and invoke the default constructor.
>Rather, it
>declares a function called stud_1 that takes no arguments and returns a
>Student object. To define a Student object, drop the brackets, i.e., use
>
>Student stud_1;[/color]

Good catch. I missed it (but I must admit I wasn't looking all that hard
any more by the time I reached that section of the post).

Ironically, this is the very item I contributed to Bruce Eckel & Chuck
Allison's "C++ Annoyances" session at SD West recently. The reason it
annoys me should now be quite apparent: I don't /notice/ it ;-)
-leor


--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:

https://www.bdsoft.com/tools/stlfilt.html

[Mike Higginbottom]

Re: Trouble with constructor

On Fri, 09 Apr 2004 20:32:06 GMT, Leor Zolman <leor@bdsoft.co m> wrote:
[color=blue][color=green]
>> Student stud_1;[/color]
>
> Good catch. I missed it (but I must admit I wasn't looking all that hard
> any more by the time I reached that section of the post).
>
> Ironically, this is the very item I contributed to Bruce Eckel & Chuck
> Allison's "C++ Annoyances" session at SD West recently. The reason it
> annoys me should now be quite apparent: I don't /notice/ it ;-)
> -leor
>
>[/color]

Not just me then ;)


--
Mike Higginbottom

http://www.peak41.co.uk

[Mike Higginbottom]

Re: Trouble with constructor

On Fri, 09 Apr 2004 20:32:06 GMT, Leor Zolman <leor@bdsoft.co m> wrote:
[color=blue][color=green]
>> Student stud_1;[/color]
>
> Good catch. I missed it (but I must admit I wasn't looking all that hard
> any more by the time I reached that section of the post).
>
> Ironically, this is the very item I contributed to Bruce Eckel & Chuck
> Allison's "C++ Annoyances" session at SD West recently. The reason it
> annoys me should now be quite apparent: I don't /notice/ it ;-)
> -leor
>
>[/color]

Not just me then ;)


--
Mike Higginbottom

http://www.peak41.co.uk

[Gary Labowitz]

Re: Trouble with constructor

"Mike Higginbottom" <news@peak41.co .uk> wrote in message
news:opr57hwusi ct0wm7@fuzzbox. ..[color=blue]
> On 9 Apr 2004 12:37:58 -0700, San <abc_99_420@hot mail.com> wrote:
>[color=green]
> > I wrote two simple constructors (one of them default) to[/color][/color]
initialize a[color=blue][color=green]
> > student object.[/color]
>
> [snip][color=green]
> > When I try to use the following:
> > Student stud_1("San");
> > The g++ compiler gives an error message "undefined message to
> > Student::Studen t(basic_string( char, string_char_tra its(char),
> > _default_alloc_ template(0,0))) "[/color]
> It would be nice to see the class declaration but the following[/color]
works fine[color=blue]
> on .NET:
>
> class Student
> {
> public:
> Student();
> Student(std::st ring name);
> private:
> std::string student_name;[/color]

I'd like to see if OP declared student_name that way. I'm thinking it
was a c-style string.
[color=blue]
> };
>[/color]

All other problems were taken care of.
--
Gary

[Gary Labowitz]

Re: Trouble with constructor

"Mike Higginbottom" <news@peak41.co .uk> wrote in message
news:opr57hwusi ct0wm7@fuzzbox. ..[color=blue]
> On 9 Apr 2004 12:37:58 -0700, San <abc_99_420@hot mail.com> wrote:
>[color=green]
> > I wrote two simple constructors (one of them default) to[/color][/color]
initialize a[color=blue][color=green]
> > student object.[/color]
>
> [snip][color=green]
> > When I try to use the following:
> > Student stud_1("San");
> > The g++ compiler gives an error message "undefined message to
> > Student::Studen t(basic_string( char, string_char_tra its(char),
> > _default_alloc_ template(0,0))) "[/color]
> It would be nice to see the class declaration but the following[/color]
works fine[color=blue]
> on .NET:
>
> class Student
> {
> public:
> Student();
> Student(std::st ring name);
> private:
> std::string student_name;[/color]

I'd like to see if OP declared student_name that way. I'm thinking it
was a c-style string.
[color=blue]
> };
>[/color]

All other problems were taken care of.
--
Gary

[San]

Re: Trouble with constructor(cod e included)

Here's the class definition:
//-----------------------------------------------------------------------------
#ifndef Student_h
#define Student_h

#include <string>

namespace stud{

class Student
{
private:
static const long LATEST_ID = 99999999;
string student_name;
long student_id;
string student_address ;
long student_phone;
string student_email;

public:
Student();

Student(std::st ring name);

}; //class student
} //namespace stud

#endif

//-----------------------------------------------------------------------------

I changed the implementation or cpp file to include the foll:

#include "Student.h"
#include <string>

namespace stud{

Student::Studen t(std::string name)
{
student_name = name;
student_id = LATEST_ID + 1;
}

Student::Studen t()
{
student_name = "";
student_id = LATEST_ID + 1;
}
} //namespace stud

//-----------------------------------------------------------------------------


The main file code contains the foll:

#include "Student.h"
using namespace std;
using namespace stud;

int main()
{
Student stud_1;
Student stud_2("San");
return 0;
}



I am aware of the advantages using initialization before the
constructor body and did start out with that. But when I came across
the errors, I thought maybe I was doing something wrong in the
initialization part and so resorted to assigment in the body.

If I have to initialize a string variable with an empty string and a
long integer with 0 isnt this the right way to do it?
Student::Studen t():student_nam e(""),student_p hone(0){}


Thanks for all the advice. The Student stud_1(); thing was really
silly of me :-)


As an aside, I have just realised that posting to Usenet using Google
incurs a long delay. Being new to the usenet community, I am trying to
find newsreaders that update posts faster. Kindly bear with me.

Thanks,
Santosh

[San]

Re: Trouble with constructor(cod e included)

Here's the class definition:
//-----------------------------------------------------------------------------
#ifndef Student_h
#define Student_h

#include <string>

namespace stud{

class Student
{
private:
static const long LATEST_ID = 99999999;
string student_name;
long student_id;
string student_address ;
long student_phone;
string student_email;

public:
Student();

Student(std::st ring name);

}; //class student
} //namespace stud

#endif

//-----------------------------------------------------------------------------

I changed the implementation or cpp file to include the foll:

#include "Student.h"
#include <string>

namespace stud{

Student::Studen t(std::string name)
{
student_name = name;
student_id = LATEST_ID + 1;
}

Student::Studen t()
{
student_name = "";
student_id = LATEST_ID + 1;
}
} //namespace stud

//-----------------------------------------------------------------------------


The main file code contains the foll:

#include "Student.h"
using namespace std;
using namespace stud;

int main()
{
Student stud_1;
Student stud_2("San");
return 0;
}



I am aware of the advantages using initialization before the
constructor body and did start out with that. But when I came across
the errors, I thought maybe I was doing something wrong in the
initialization part and so resorted to assigment in the body.

If I have to initialize a string variable with an empty string and a
long integer with 0 isnt this the right way to do it?
Student::Studen t():student_nam e(""),student_p hone(0){}


Thanks for all the advice. The Student stud_1(); thing was really
silly of me :-)


As an aside, I have just realised that posting to Usenet using Google
incurs a long delay. Being new to the usenet community, I am trying to
find newsreaders that update posts faster. Kindly bear with me.

Thanks,
Santosh