ostream as parameter for constructor

[Art Werschulz]

Hi.

I would like one of the constructors for a given class to take an
ostream as a parameter.

The following example (foo.cc) doesn't work:

---%<------%<------%<------%<--Cut-Here-%<------%<------%<------%<------
#include <iostream>
#include <string>

class X {
public:
X(std:stream os_param=std::cout): os(os_param) {}
void print(std::string s) { os << s; }
private:
std:stream os;
};

int main()
{
X x(std::cerr);
x.print("hello, world\n");

return 0;
}
---%<------%<------%<------%<--Cut-Here-%<------%<------%<------%<------

I get the following error msg (slightly reformatted to fit the line width):

foo.cc: In copy constructor `std::basic_ios<char,
std::char_traits<char> >::basic_ios(const std::basic_ios<char,
std::char_traits<char> >&)':
/usr/include/gcc/darwin/4.0/c++/bits/ios_base.h:736: error:
'std::ios_base::ios_base(const std::ios_base&)' is private
foo.cc:6: error: within this context

(Line 6 of foo.cc is the definition of the X constructor.)

Suggestions? Thanks.

 

[Piyo]

Suggestions? Thanks.

Try this instead:
HTH!!

#include <iostream>
#include <string>

class X {
public:
X(std:stream &os_param=std::cout): os(os_param) {}
void print(std::string s) { os << s; }
private:
std:stream &os;
};

int main()
{
X x(std::cerr);
x.print("hello, world\n");

return 0;
}

 

[John Harrison]

Hi.

I would like one of the constructors for a given class to take an
ostream as a parameter.

The following example (foo.cc) doesn't work:

---%<------%<------%<------%<--Cut-Here-%<------%<------%<------%<------
#include <iostream>
#include <string>

class X {
public:
X(std:stream os_param=std::cout): os(os_param) {}
void print(std::string s) { os << s; }
private:
std:stream os;
};

int main()
{
X x(std::cerr);
x.print("hello, world\n");

return 0;
}
---%<------%<------%<------%<--Cut-Here-%<------%<------%<------%<------

I get the following error msg (slightly reformatted to fit the line width):

foo.cc: In copy constructor `std::basic_ios<char,
std::char_traits<char> >::basic_ios(const std::basic_ios<char,
std::char_traits<char> >&)':
/usr/include/gcc/darwin/4.0/c++/bits/ios_base.h:736: error:
'std::ios_base::ios_base(const std::ios_base&)' is private
foo.cc:6: error: within this context

(Line 6 of foo.cc is the definition of the X constructor.)

Suggestions? Thanks.

streams are not copyable. You must pass a reference or a pointer to a
stream, for instance

class X {
public:
X(std:stream& os_param=std::cout): os(&os_param) {}
void print(std::string s) { (*os) << s; }
private:
std:stream* os;
};

john

 

[Doug]

Hi.

I would like one of the constructors for a given class to take an
ostream as a parameter.

The following example (foo.cc) doesn't work:

---%<------%<------%<------%<--Cut-Here-%<------%<------%<------%<------
#include <iostream>
#include <string>

class X {
public:
X(std:stream os_param=std::cout): os(os_param) {}
void print(std::string s) { os << s; }
private:
std:stream os;
};

int main()
{
X x(std::cerr);
x.print("hello, world\n");

return 0;
}
---%<------%<------%<------%<--Cut-Here-%<------%<------%<------%<------

I get the following error msg (slightly reformatted to fit the line width):

foo.cc: In copy constructor `std::basic_ios<char,
std::char_traits<char> >::basic_ios(const std::basic_ios<char,
std::char_traits<char> >&)':
/usr/include/gcc/darwin/4.0/c++/bits/ios_base.h:736: error:
'std::ios_base::ios_base(const std::ios_base&)' is private
foo.cc:6: error: within this context

(Line 6 of foo.cc is the definition of the X constructor.)

Suggestions? Thanks.

Hiya,

This is a guess, but I doubt you can pass a std:stream by value.
Passing by value will invoke the copy ctor, and a copy ctor for
std:stream doesn't make much sense to me.

Try passing the ostream by pointer?

I'm probably wrong, but don't have a compiler or any source to check.
Good luck.

Doug

 

[Art Werschulz]

Hi.

Thanks for your suggestions.