โดยย่อ "ฉันจะลบออกจากแผนที่ขณะทำซ้ำได้อย่างไร"
- ด้วย impl map แบบเก่า: คุณทำไม่ได้
- ด้วย impl map ใหม่: เกือบจะเป็น @KerrekSB ที่แนะนำ แต่มีปัญหาทางไวยากรณ์บางอย่างในสิ่งที่เขาโพสต์
จากแผนที่ GCC impl (หมายเหตุGXX_EXPERIMENTAL_CXX0X ):
#ifdef __GXX_EXPERIMENTAL_CXX0X__
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// DR 130. Associative erase should return an iterator.
/**
* @brief Erases an element from a %map.
* @param position An iterator pointing to the element to be erased.
* @return An iterator pointing to the element immediately following
* @a position prior to the element being erased. If no such
* element exists, end() is returned.
*
* This function erases an element, pointed to by the given
* iterator, from a %map. Note that this function only erases
* the element, and that if the element is itself a pointer,
* the pointed-to memory is not touched in any way. Managing
* the pointer is the user's responsibility.
*/
iterator
erase(iterator __position)
{ return _M_t.erase(__position); }
#else
/**
* @brief Erases an element from a %map.
* @param position An iterator pointing to the element to be erased.
*
* This function erases an element, pointed to by the given
* iterator, from a %map. Note that this function only erases
* the element, and that if the element is itself a pointer,
* the pointed-to memory is not touched in any way. Managing
* the pointer is the user's responsibility.
*/
void
erase(iterator __position)
{ _M_t.erase(__position); }
#endif
ตัวอย่างที่มีสไตล์เก่าและใหม่:
#include <iostream>
#include <map>
#include <vector>
#include <algorithm>
using namespace std;
typedef map<int, int> t_myMap;
typedef vector<t_myMap::key_type> t_myVec;
int main() {
cout << "main() ENTRY" << endl;
t_myMap mi;
mi.insert(t_myMap::value_type(1,1));
mi.insert(t_myMap::value_type(2,1));
mi.insert(t_myMap::value_type(3,1));
mi.insert(t_myMap::value_type(4,1));
mi.insert(t_myMap::value_type(5,1));
mi.insert(t_myMap::value_type(6,1));
cout << "Init" << endl;
for(t_myMap::const_iterator i = mi.begin(); i != mi.end(); i++)
cout << '\t' << i->first << '-' << i->second << endl;
t_myVec markedForDeath;
for (t_myMap::const_iterator it = mi.begin(); it != mi.end() ; it++)
if (it->first > 2 && it->first < 5)
markedForDeath.push_back(it->first);
for(size_t i = 0; i < markedForDeath.size(); i++)
// old erase, returns void...
mi.erase(markedForDeath[i]);
cout << "after old style erase of 3 & 4.." << endl;
for(t_myMap::const_iterator i = mi.begin(); i != mi.end(); i++)
cout << '\t' << i->first << '-' << i->second << endl;
for (auto it = mi.begin(); it != mi.end(); ) {
if (it->first == 5)
// new erase() that returns iter..
it = mi.erase(it);
else
++it;
}
cout << "after new style erase of 5" << endl;
// new cend/cbegin and lambda..
for_each(mi.cbegin(), mi.cend(), [](t_myMap::const_reference it){cout << '\t' << it.first << '-' << it.second << endl;});
return 0;
}
พิมพ์:
main() ENTRY
Init
1-1
2-1
3-1
4-1
5-1
6-1
after old style erase of 3 & 4..
1-1
2-1
5-1
6-1
after new style erase of 5
1-1
2-1
6-1
Process returned 0 (0x0) execution time : 0.021 s
Press any key to continue.