Accelerated C++：通过示例进行编程实践——练习解答（第6章）

说明：从本章开始除了思路分析或者不需要代码的题目，其他涉及代码的题目就不再这里帖出代码了（重复和费时间），源代码全部放在了GitHub里我的Github地址：https://github.com/lanbeilyj/Accerlerated-C-plus-plus。

6-0.    Compile, execute, and test the programs in this chapter.

见github。

6-1.    Reimplement the

frame

and

hcat

operations from §5.8.1/93 and §5.8.3/94 to use iterators.

见github。

6-2.    Write a program to test the

find_urls

function.

见github。

6-3.    What does this program fragment do?

vector<int> u(10, 100);
vector<int> v;
copy(u.begin(), u.end(), v.begin());

Write a program that contains this fragment, and compile and execute it.

Ans：本题作者的目的是初始化一个含有10个值为100的容器，然后将该容器的每个值copy给另一个新的空容器；但是作者的copy算法调用是错误的，因为v为空所以v.begin()是一个并不存在的元素，对其复制的结果是未定义，提示segment error！如本书所介绍，copy算法这么设计是区分复制和扩展容易的概念。当v含有k个元素时则只是复制k个u中的值到v中，而u中多余的值并不能复制；当第三个参数为迭代器适配器时，则copy会将u中所有元素全部复制给v，若v的容量不足则会扩展以容纳u中的元素。

所以应该修改为：copy(u.begin(),u.end(),back_inserter(v));

6-4.   Correct the program you wrote in the previous exercise to copy from

u

into

v

. There are at least two possible ways to correct the program. Implement both, and describe the relative advantages and disadvantages
of each approach.

Ans：1、vector<int> v(u.begin(),u.end());

          2、vector<int> v; v=u;

第二种等价于首先将v容器清空即v.erase(v.begin(),v.end())，然后再插入v.insert(u.begin(),u.end(),v.begin())；而第一种实质也是insert故相比较第一种优于第二种，但是对这个例子并不明显。

6-5.   Write an analysis function to call

optimistic_median

.

见github。

6-6.   Note that the function from the previous exercise and the functions from §6.2.2/113 and §6.2.3/115 do the same task. Merge these three analysis functions into a single function.

见github。

6-7.   The portion of the grading analysis program from §6.2.1/110 that read and classified student records depending on whether they did (or did not) do all the homework is similar to the problem we solved in

extract_fails

.
Write a function to handle this subproblem.

见github。

6-8.   Write a single function that can be used to classify students based on criteria of your choice. Test this function by using it in place of the

extract_fails

program, and use it in the program to analyze student grades.

Ans：感觉这题意义不大，只是根据条件分类来push_back，然后就是分别调用，为了让读者更熟悉这种算法吧。见github。

6-9.   Use a library algorithm to concatenate all the elements of a

vector<string>

.

Ans：需要连接字符串故想到用库算法accumulate(begin,end,string)，第三个参数表示一字符串我们将其表示为：string s=accumulate(v.begin(),v.end(),string(""));具体代码见github。