back_inserter() and string

This won't work in VC++6:

Code:

#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

int main()
{
	const int size = 3;
	char myArray[size] = {'y', 'e', 's'};
	
	string str;
	copy(myArray, myArray + size, back_inserter(str));
	cout<<str<<endl;

	return 0;
};

I get the error:

error C2039: 'push_back' : is not a member of 'basic_string<char,struct std::char_traits<char>,class std::allocator<char> >'
c:\program files\c++microsoft visual studio\vc98\include\iterator(82) : while compiling class-template member function 'class std::back_insert_iterator<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >
&__thiscall std::back_insert_iterator<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >::operator =(const char &)'
Error executing cl.exe.

back_inserter() calls push_back() for the container, and the string class has a push_back() member function, so is that a compiler bug, or am I doing something wrong?

Looks like a MSVC6 bug, or rather a pre-standard implementation of basic_string that lacks push_back(). A quick search seems to confirm that.

It works on MSVC8 and MinGW port of GCC 3.4.2

A quick search seems to confirm that.

I went to dinkumware and looked at their list of library fixes for VC5 and VC6, but they don't have anything listed for that.

Looks like a MSVC6 bug, or rather a pre-standard implementation of basic_string that lacks push_back()

When I click on the error in VC6, it takes me here:

Code:

// TEMPLATE CLASS back_insert_iterator
template<class _C>
	class back_insert_iterator
		: public iterator<output_iterator_tag, void, void> {
public:
	typedef _C container_type;
	typedef _C::value_type value_type;
	explicit back_insert_iterator(_C& _X)
		: container(_X) {}
	back_insert_iterator<_C>& operator=(
		const value_type& _V)
		{container.push_back(_V);
		return (*this); }
	back_insert_iterator<_C>& operator*()
		{return (*this); }
	back_insert_iterator<_C>& operator++()
		{return (*this); }
	back_insert_iterator<_C> operator++(int)
		{return (*this); }

So, it looks like push_back() is in there, but for some reason it doesn't work.

Thanks.

I went to dinkumware and looked at their list of fixes for VC5 and VC6, but that don't have anything listed for that.

I did that too after replying :P
Does seem very strange. Have you tried using string::push_back() directly, to confirm that it isnt a problem with back_inserter()'s implementation?

EDIT:
okay, so it gets stranger and stranger.

So, it looks like push_back() is in there, but for some reason it doesn't work.

hmm... isnt that just the use of push_back()? If the class type doesnt have a push_back(), then it should complain about it, just like what its doing.

Originally Posted by laserlight

I did that too after replying :P
Does seem very strange. Have you tried using string::push_back() directly, to confirm that it isnt a problem with back_inserter()'s implementation?

Nope. I wasn't smart enough to think of that. This doesn't work either:

Code:

#include <iostream>
#include <string>
using namespace std;

int main()
{
	string str = "hello";
	cout<<str<<endl;

	str.push_back('a');
	cout<<str<<endl;

	return 0;
};

error C2039: 'push_back' : is not a member of 'basic_string<char,struct std::char_traits<char>,class std::allocator<char> >'
Error executing cl.exe.

On second thought, that error in red I posted doesn't mean push_back() is present in the string class: the code is trying to call push_back() for the container, and apparently the compiler can't find it.

I found this small snippet on google:

VC6 has a pre-standard library in which std::string::push_back is not
present, which might be the source of the confusion.

Maybe that can be fixed. If MSVC6's implementation of of basic_string has insert() and end(), one might be able to implement push_back() with the equivalent of an insert(end(), char_value)

Yep. There are many different ways to accomplish the same thing, e.g. append(), insert(). I was exploring some of the alternatives when I discovered that back_inserter() wouldn't work.

+= is another option - the only one actually that can simply take a single character.
The problem is that std::string is precompiled in MSVC - you cannot simply change the source and expect it to work.

+= is another option

I don't really see how. The idea was to insert a range of values into a string.

Could be that CornedBee meant that operator+= could be used to implement push_back().

I was talking about its parallel to push_back(), as laserlight described, not its relation to the original question.

Of course, insert() or append() or even assign() are a better choice even than std::copy for the original problem.