C++ Primer(第五版) 9.3.4--9.3.6节练习_c++primer练习9.30

9.27 

#include <iostream>
#include <forward_list>
 
using namespace std;
 
int main()
{
	forward_list<int> flist = {1, 2, 3, 4, 5, 6, 7, 8};
	
	auto prev = flist.before_begin();
	auto curr = flist.begin();
 
	while (curr != flist.end()) {
		if ((*curr)%2)
			curr = flist.erase_after(prev);
		else {
			prev = curr;
			++curr;
		}
	}
 
	for (auto i : flist)
		cout << i << endl;
 
	return 0;
}

9.28

#include <iostream> 
#include <forward_list>
 
using namespace std;
 
void flist_insert(forward_list<string> &flist, const string s1, const string s2)
{
	auto prev = flist.before_begin();
	auto curr = flist.begin();
	bool insert = false;
	
	while (curr != flist.end()) {
		if (*curr == s1) {
			curr = flist.insert_after(curr, s2);
			prev = curr; 
			++curr;
			insert = true;
		} else {
			prev = curr;
			++curr;
		}
	}
 
	if (!insert) {
		flist.insert_after(prev, s2);
	}
}
 
int main()
{
	forward_list<string> flist = {"s1", "s2", "s3", "s4", "s2", "s6"};
 
	flist_insert(flist, "s2", "s5");
 
	for (auto s : flist)
		cout << s << endl;
 
	flist_insert(flist, "s6", "s8");
 
	for (auto s : flist)
		cout << s << endl;
	
/* 所有元素都相同的情况 */
	forward_list<string> flist2 = {"s1", "s1", "s1", "s1"};
	flist_insert(flist2, "s1", "s1");
 
	for (auto s : flist2)
		cout << s << endl;
 
	return 0;
}

9.29    vec.resize(100)会向末尾新增75个元素，这些元素进行值初始化；vec.resize(10)会删除末尾的90个元素。

9.30    接受单个参数，要求该元素类型有默认构造函数。

9.31    list和forward_list的元素在内存中不连续，不支持迭代器的加减运算。修改程序如下：

#include <iostream>
#include <list>
#include <forward_list>
 
using namespace std;
 
int main()
{
	list<int> ilist = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
	forward_list<int> flist = {0, 1, 2, 3, 4, 5, 6 ,7, 8, 9};
 
	auto iter = ilist.begin();
	while (iter != ilist.end()) {
		if (*iter % 2) {
			iter = ilist.insert(iter, *iter);
			++iter;
			++iter;
		} else {
			iter = ilist.erase(iter);
		}
	}
 
	for (auto i : ilist)
		cout << i << endl;
 
	auto prev = flist.before_begin();
	auto curr = flist.begin();
	while (curr != flist.end()) {
		if (*curr % 2) {
			curr = flist.insert_after(prev, *curr);
			prev = ++curr;
			++curr;
		} else {
			curr = flist.erase_after(prev);
			
		}
	}
 
	for (auto f : flist)
		cout << f << endl;
 
	return 0;
}

932.    不合法，编译时会先计算第二个参数 *iter++， iter指向当前奇数的下一个元素，导致第一个参数的值错误。

9.33    向vector添加元素后，指向容器的迭代器，指针和引用都可能失效，不将insert结果赋予begin，begin会失效，继续使用可能导致程序崩溃。

9.34    该代码的目的是复制奇数元素； 代码错误：++iter应该被包括在循环体内，且应该多执行一次++iter。修改如下：

#include <iostream>
#include <vector>
 
using namespace std;
 
int main()
{
	vector<int> vi = {1, 2, 3, 4, 5, 6, 7, 8, 9};
 
	auto iter = vi.begin();
	while (iter != vi.end()) {
		if (*iter % 2) {
			iter = vi.insert(iter, *iter);
			++iter;
		}
		++iter;
	}
 
	for (auto v : vi)
		cout << v << endl;
 
	return 0;
}