I've had to comment out the line //*it = 8; but the rest works under VC8 and increments the value in the vector:
struct f : public std::unary_function {
int operator()(int x) const { return ++x; } };
typedef std::vector<int> vec_type;
typedef boost::transform_iterator trans_iter_type;
int _tmain(int argc, _TCHAR* argv[]) {
vec_type V;
V.push_back(4);
trans_iter_type it(boost::make_transform_iterator(V.begin(),f()));
std::cout << *it << std::endl;
//*it = 8;
std::cout << *it << std::endl;
return 0;
}
-----Original Message-----
From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Nicola
Sent: 11 April 2008 10:11
To: boost-users@lists.boost.org
Subject: [Boost-users] [iterator] Writable transform_iterator: how to?
Hello,
I cannot figure out why the following code is wrong:
#include <iostream>
#include <vector>
#include <functional>
#include
struct f : public std::unary_function {
int& operator()(int& x) { return x; }
};
typedef std::vector<int> vec_type;
typedef boost::transform_iterator trans_iter_type;
int main() {
vec_type V;
V.push_back(4);
trans_iter_type it(boost::make_transform_iterator(V.begin(), f()));
std::cout << *it << std::endl;
*it = 8;
std::cout << *it << std::endl;
return 0;
}
The compiler (g++ 4.0.1) complains about dereferencing and the error
message says:
error: passing ‘const f’ as ‘this’ argument of ‘int&
f::operator()(int&)’ discards qualifiers
Nicola
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