printing out to files

[mbcx7mm3]

i Have a pure virtual function called print(). In each of my derived classed i have the function with it giving the commands

cout<<information<<number<<endl;

This works fine, but i want to print out the data to an outputfile which i have created in my main code. When i add the following to the print function to make it

cout<<information<<number<<endl;
out<<information<<number<<endl;

I get the error ' out was not declared in this scope '. Anybody know why this is and how i can correct it?

[ne555]

print(std::ostream &out);

[mbcx7mm3]

i was able to get this into my classes without any errors but unfortunately when i call it in my main adn go to the output file nothing is printed.

THIS IS MY PURE VIRTUAL FUNCTION IN MY ABSTRACT BASE CLASS:

virtual void printf(std::ostream &out)=0;

THIS IS THE FUNCTION WRITTEN IN EACH OF THE DERIVED CLASSES.
void printf(std::ostream &out)
{
out<<"Student name: "<<sname<<" Student ID:"<<stdid<<endl<<endl<<lecture<<endl;
}

Withing the main i have made an out put file

const char outfile[]= "STD.txt";
ofstream out(outfile);

I attempted to call the function using

(*sdatait)->printf(out);

I am using iterators to print out. This line worked fine on the simple print() function which just printed the information to the command window.

Do you know how to correct this?

[benjelly]

1) Please use legitimate English and correct your typos. I don't want to solve your words, I want to solve your problem.

2) The topic title is very vague. I see so many topics like this. Gee, why don't I pull out a gun and shoot everyone who makes these topics? According to Hitler, that works great for making the world a better place. But sorry mbcx7mm3 (your name? what the hell??), I'm not radical.

I get the error ' out was not declared in this scope '. Anybody know why this is and how i can correct it?

Wait are we still trying to correct that problem?

[mbcx7mm3]

Apologies if i have annoyed you, mbcx7mm3 is just my username from work. And the typos, are because i am slightly dyslexic. I am relatively new to C++ and i am trying my best to learn.

Basically this is my issue,

I have a pure virtual function defined within my abstract base class 'virtual void print()=0;' . Within my derived class which is called 'physics' the function is coded as:

void print()
{

cout<<"Faculty: PHYSICS - Student name: "<<sname<<" - Student ID:"<<stdid<<" "<<endl<<endl<<lec<<endl;

}

This works fine, and prints out to the command window. However, i wish to also print out to a file and currently i can only do this by using the command within my main:

out<<physics;

i wish to however have a similar function as print() contained within my derived class which will print out to a file, calling the function printf(). Why is it not possible to write:

void printf()
{

out<<"Faculty: PHYSICS - Student name: "<<sname<<" - Student ID:"<<stdid<<" "<<endl<<endl<<lec<<endl;

}

[ne555]

[code] "Please use code tags" [/code]
what happen if you use (*it)->printf(std::cout); ?
Is the file created?

Post the calls and the definition of the methods

[mbcx7mm3]

I have created the file already at the start of the main by

const char outfile[]= "STD.txt";	//Output file to print the student data to an output textfile with the name 'STD.txt'
	ofstream out(outfile);

The function to print out to this file which is in my class is (which unfortunately doesn't work)

void prinf(std::ostream &out)
	{
		out<<"|Faculty: PHYSICS\n | Student name: "<<sname<<" | Student ID:"<<stdid<<" | "<<endl<<endl<<lec<<endl;
	}

when i used (*sdataIter).second->printf(std::cout);

I got three errors talking about:-

typeinfo for abstract base class
vtable for absract base class

saying something about them being referenced from my derived classes. The errors, were really quite difficult to understand.

[ne555]

Paste the errors.
This works for me

#include <iostream>
#include <fstream>
#include <vector>
#include <memory>

class A{
public:
	virtual void printf(std::ostream &) = 0;
};

class B:public A{
public:
	virtual void printf(std::ostream &out){
		out<<'B';
	}
};

class C:public A{
public:
	virtual void printf(std::ostream &){
		out<<'C';
	}
};

int main(int argc, char **argv){
	std::vector< A* > v;
	std::ofstream out("test");
	v.push_back( new B );
	v.push_back( new C );
	for(size_t K=0; K<v.size(); ++K)
		v[K]->printf(std::cout);
	for(std::vector<A*>::iterator it=v.begin(); it!=v.end(); ++it)
		(*it)->printf(out);

	for(size_t K=0; K<v.size(); ++K)
		delete v[K];
	return 0;
}

[mbcx7mm3]

The errors that i got were,

"typeinfo for student", referenced from:
typeinfo for physicsin main.o
typeinfo for chemistryin main.o
typeinfo for biologyin main.o


"vtable for student", referenced from:
student::~student()in main.o
student::~student()in main.o
student::student()in main.o
student::student(std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int)in main.o

"student::printf(std::basic_ofstream<char, std::char_traits<char> >&)", referenced from:
vtable for chemistryin main.o
vtable for biologyin main.o


ld: symbol(s) not found
collect2: ld returned 1 exit status

thanks

[ne555]

I need more context
http://www.cplusplus.com/forum/articles/40071/#msg216270
http://www.cplusplus.com/forum/articles/40071/#msg216313

[Ambeco]

"student::printf(std::basic_ofstream<char, std::char_traits<char> >&)", referenced from:

This means your student::printf function was never defined. This is usually because the coder forgot to declare it as a pure virtual function with "=0"

class student { 
public: 
    virtual void printf(std::ostream &) = 0; 
}

"vtable for student", referenced from:

Given the above error, I'd guess you also forgot to add the virtual keyword, resulting in a student class with no vtable.

"typeinfo for student", referenced from:

I'm not sure what would cause this. Correct the other errors, and then show us the entire student class if the problem is still there.