Programming Forums > Application Development > C++

Jessehk · Apr 27th, 2006, 8:13 PM

Scripting languages make programming fun, but sometimes half the fun is working creating something yourself.

I was trying to make my own String class to get my C++ memory back.
For some reason, when I try to invoke a function that I specifically made a friend, I get this error:

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$ g++ myString.cpp main.cpp -o string
myString.cpp: In function �std::ostream& operator<<(std::ostream&, const Jesse::String&)�:
myString.h:9: error: �char* Jesse::String::str� is private
myString.cpp:13: error: within this context

Which tells me that I am doing something wrong. The problem is that I have no idea what it is. Help would be appreciated.

myString.h

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#include <iostream>

#ifndef MYSTRING_H_
#define MYSTRING_H_

namespace Jesse {
	class String {
		private:
			char *str;
			size_t size;
		public:
			String(const char *string);
			friend std::ostream &operator<<(std::ostream &os, const Jesse::String &str);
			size_t length() const;
			virtual ~String();
	};
}

#endif

myString.cpp

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#include "myString.h"

#include <cstring>
#include <iostream>

Jesse::String::String(const char *string)
	: size(strlen(string)) {

	str = new char[size];
	strcpy(str, string);
}

std::ostream &operator<<(std::ostream &os, const Jesse::String &string) {
	os << string.str;
	return os;
}

size_t Jesse::String::length() const {
	return size;
}

Jesse::String::~String() {
	delete [] str;
}

main.cpp

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#include "myString.h"

#include <iostream>

int main() {
	Jesse::String str("Hello, world!");

	std::cout << str;

	return 0;
}

Thanks

Narue · Apr 27th, 2006, 8:28 PM

Wrap your implementation in the Jesse namespace too. Your problem isn't the friend function, it's a namespace scoping ambiguity:

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#include "myString.h"

#include <cstring>
#include <iostream>

namespace Jesse {
    String::String(const char *string)
	: size(strlen(string)) {

	str = new char[size];
	strcpy(str, string);
    }

    std::ostream &operator<<(std::ostream &os, const String &string) {
	os << string.str;
	return os;
    }

    size_t String::length() const {
	return size;
    }

    String::~String() {
	delete [] str;
    }
}

You could also qualify operator<< as Jesse::operator<<, but it's easier to see the namespace structure by extending the namespace to hold your implementation code as well.

Jessehk · Apr 27th, 2006, 8:34 PM

That fixed it. Thanks Narue!

Apr 27th, 2006, 8:13 PM	#1
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	friend functions causing trouble Scripting languages make programming fun, but sometimes half the fun is working creating something yourself. I was trying to make my own String class to get my C++ memory back. For some reason, when I try to invoke a function that I specifically made a friend, I get this error: (Toggle Plain Text) $ g++ myString.cpp main.cpp -o string myString.cpp: In function �std::ostream& operator<<(std::ostream&, const Jesse::String&)�: myString.h:9: error: �char* Jesse::String::str� is private myString.cpp:13: error: within this context $ g++ myString.cpp main.cpp -o string myString.cpp: In function �std::ostream& operator<<(std::ostream&, const Jesse::String&)�: myString.h:9: error: �char* Jesse::String::str� is private myString.cpp:13: error: within this context Which tells me that I am doing something wrong. The problem is that I have no idea what it is. Help would be appreciated. myString.h (Toggle Plain Text) #include <iostream> #ifndef MYSTRING_H_ #define MYSTRING_H_ namespace Jesse { class String { private: char str; size_t size; public: String(const char string); friend std::ostream &operator<<(std::ostream &os, const Jesse::String &str); size_t length() const; virtual ~String(); }; } #endif #include <iostream> #ifndef MYSTRING_H_ #define MYSTRING_H_ namespace Jesse { class String { private: char str; size_t size; public: String(const char string); friend std::ostream &operator<<(std::ostream &os, const Jesse::String &str); size_t length() const; virtual ~String(); }; } #endif myString.cpp (Toggle Plain Text) #include "myString.h" #include <cstring> #include <iostream> Jesse::String::String(const char string) : size(strlen(string)) { str = new char[size]; strcpy(str, string); } std::ostream &operator<<(std::ostream &os, const Jesse::String &string) { os << string.str; return os; } size_t Jesse::String::length() const { return size; } Jesse::String::~String() { delete [] str; } #include "myString.h" #include <cstring> #include <iostream> Jesse::String::String(const char string) : size(strlen(string)) { str = new char[size]; strcpy(str, string); } std::ostream &operator<<(std::ostream &os, const Jesse::String &string) { os << string.str; return os; } size_t Jesse::String::length() const { return size; } Jesse::String::~String() { delete [] str; } main.cpp (Toggle Plain Text) #include "myString.h" #include <iostream> int main() { Jesse::String str("Hello, world!"); std::cout << str; return 0; } #include "myString.h" #include <iostream> int main() { Jesse::String str("Hello, world!"); std::cout << str; return 0; } Thanks __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Apr 27th, 2006, 8:28 PM	#2
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	Wrap your implementation in the Jesse namespace too. Your problem isn't the friend function, it's a namespace scoping ambiguity: (Toggle Plain Text) #include "myString.h" #include <cstring> #include <iostream> namespace Jesse { String::String(const char string) : size(strlen(string)) { str = new char[size]; strcpy(str, string); } std::ostream &operator<<(std::ostream &os, const String &string) { os << string.str; return os; } size_t String::length() const { return size; } String::~String() { delete [] str; } } #include "myString.h" #include <cstring> #include <iostream> namespace Jesse { String::String(const char string) : size(strlen(string)) { str = new char[size]; strcpy(str, string); } std::ostream &operator<<(std::ostream &os, const String &string) { os << string.str; return os; } size_t String::length() const { return size; } String::~String() { delete [] str; } } You could also qualify operator<< as Jesse::operator<<, but it's easier to see the namespace structure by extending the namespace to hold your implementation code as well. __________________ Even if the voices aren't real, they have some pretty good ideas.

Apr 27th, 2006, 8:34 PM	#3
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	That fixed it. Thanks Narue! __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

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Programming Forums > Application Development > C++

friend functions causing trouble