stl的问题求教[c++]

dany

3. #include <iostream>
4. #include <set>
5. #include <algorithm>
6. #include <iterator>
7.        
8. using namespace std;
11. int main() {
12.         set<int> col1;
13.         for(int i=0;i<10;i++) {
14.                 col1.insert(i);
15.         }
16.        
17.        
18.         transform(col1.begin(),col1.end(),
19.                 col1.begin(),
20.                 bind2nd (multiplies<int>(), 2));
22.         copy(col1.begin(),col1.end(), ostream_iterator<int>(cout," "));
23.         cout<<endl;
24. }

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在visual c++ 2005下面compile通过
cl -nologo -EHsc -GR -Zc:forScope -Zc:wchar_t -Fetransform transform2.cpp

在cygwin下面出错
$ g++ -o transform transform2.cpp
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_algo.h: In function `_Out
putIterator std::transform(_InputIterator, _InputIterator, _OutputIterator, _Una
ryOperation) [with _InputIterator = std::_Rb_tree_const_iterator<int>, _OutputIt
erator = std::_Rb_tree_const_iterator<int>, _UnaryOperation = std::binder2nd<std
::multiplies<int> >]':
transform2.cpp:18:   instantiated from here
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_algo.h:789: error: assign
ment of read-only location

mingw下面同样的问题
D:\cpp>g++ -otransform2 transform2.cpp
d:/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_alg
o.h: In function `_OutputIterator std::transform(_InputIterator, _InputIterator,
_OutputIterator, _UnaryOperation) [with _InputIterator = std::_Rb_tree_const_it
erator<int>, _OutputIterator = std::_Rb_tree_const_iterator<int>, _UnaryOperatio
n = std::binder2nd<std::multiplies<int> >]':
transform2.cpp:18:   instantiated from here
d:/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/stl_alg
o.h:789: error: assignment of read-only location

请高人指点一二。不胜感激。

dany

问题已经解决,应该是属于编译器的问题(编译器对于set的读取权限不一致).将set改为vector就可以实现在vc和gcc下都编译通过

2. #include <iostream>
3. #include <vector>
4. #include <algorithm>
5. #include <iterator>
6. #include <functional>
8. using namespace std;
11. int main() {
12. vector<int> col1;
13. for(int i=0;i<10;i++) {
14. col1.push_back(i);
15. }
18. transform(col1.begin(),col1.end(),
19. col1.begin(),
20. bind2nd (multiplies<int>(), 2));
22. copy(col1.begin(),col1.end(), ostream_iterator<int>(cout," "));
23. cout<<endl;
24. }

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同时加上#include <functional> 在sunstudio10上面也编译通过ok!

x11

1、代码最好用code标签
2、这关编译器什么事，是stl实现不一样吧

manphiz

的确。 libstdc++ 里 std::set::begin() 返回的 std::set::iterator 是 _Rep_type::const_iterator ，而不是 _Rep_type::iterator 。
libstdc++ 的头文件里有这样的注解：

2.       // _GLIBCXX_RESOLVE_LIB_DEFECTS
3.       // DR 103. set::iterator is required to be modifiable,
4.       // but this allows modification of keys.

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也就是说，当前 libstdc++ 的实现是为了保证键值不能被修改而作出的牺牲。而标准中说明 std::set::iterator 要求是可以修改的，但这样就会允许修改 set 的键值。当前的提交审议的解决方案是：

2. Proposed resolution:
4. Add the following to 23.1.2 [associative.reqmts] at the indicated location:
6.     At the end of paragraph 3: "For any two keys k1 and k2 in the same container, calling comp(k1, k2) shall always return the same value."
8.     At the end of paragraph 5: "Keys in an associative container are immutable."
10.     At the end of paragraph 6: "For associative containers where the value type is the same as the key type, both iterator and const_iterator are constant iterators. It is unspecified whether or not iterator and const_iterator are the same type."

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最后一段说，当值类型与键类型相同时， set::iterator 和 set::const_iterator 都将是常量迭代器。也就是说，如果该议题通过，楼主第一个 set 的例子将是不成立的。当然这还没有最终定案。

dany

谢谢manphiz的耐心解释,受益非浅.Thank you very much!