除了iterator 類型每個容器還定義了一個const iterator 類型,后者對于遍歷const 容器
是必需的const iterator 允許以只讀方式訪問容器的底層元素,例如
#include <vector >
void even_odd( const vector<int> *pvec,
vector<int> *pvec_even,
vector<int> *pvec_odd )
{
// 必須聲明一個const_iterator, 才能夠遍歷pvec
vector<int>::const_iterator c_iter = pvec->begin();
vector<int>::const_iterator c_iter_end = pvec->end();
for ( ; c_iter != c_iter_end; ++c_iter )
if ( *c_iter % 2 )
pvec_odd->push_back( *c_iter );
else pvec_even->push_back( *c_iter );
}
void print(const vector<int> *vec,vector<int>*vec_even,vector<int>*vec_odd)
{
?vector<int>::const_iterator ite_be=vec->begin();
?vector<int>::const_iterator ite_end=vec->end();
?for(;ite_be!=ite_end;ite_be++)
?{
??? if(*ite_be%2)
???? vec_even->push_back(*ite_be);
??? else
???? vec_odd->push_back(*ite_be);
?}
};
這個是錯誤的。
void print(const vector<int> vec,vector<int>vec_even,vector<int>vec_odd)
{
?vector<int>::const_iterator ite_be=vec.begin();
?vector<int>::const_iterator ite_end=vec.end();
?for(;ite_be!=ite_end;ite_be++)
?{
??? if(*ite_be%2)
???? vec_even.push_back(*ite_be);
??? else
???? vec_odd.push_back(*ite_be);
?}
};
調用
?? vector<int>vec_even;
?? vector<int>vec_odd;
? print(&vec,&vec_even,&vec_odd);
? vector<int>::iterator ite_be=vec_even.begin();
? for(;ite_be!=vec_even.end();++ite_be)
? {
???? cout<<*ite_be<<endl;
? }
? vector<int>vec_even2;
? vector<int>vec_odd2;
? print(vec,vec_even2,vec_odd2);
?? for(vector<int>::iterator ite_be=vec_even2.begin();ite_be!=vec_even2.end();++ite_be)
? {
???? cout<<*ite_be<<endl;
? }