可以使用"shared_ptr p(new Derived_Class(para));"的形式, 动态绑定派生的类;
可以为动态基类添加一个接口(interface), 使用友元函数, 访问基类的私有成员变量; 并把具体操作写入接口中;
如果一个派生类, 没有实现抽象基类的纯虚函数, 则会继承此函数, 那么这个派生类也是抽象基类;
抽象基类不能创建具体的对象, 但是可以实现具体的方法, 为派生类提供继承;
面向对象
编程: 抽象(abstraction), 即数据抽象(data abstraction);继承(inheritance);多态(polynorphism), 即动态绑定(dynamic binding).
具体代码如下, 详见注释:
[cpp]
/*
* cppprimer.cpp
*
* Created on: 2013.11.7
* Author: Caroline
*/
/*eclipse cdt, gcc 4.8.1*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
using namespace std;
class QueryResult;
std::ostream& print(std::ostream& os, const QueryResult &qr);
class TextQuery {
public:
using line_no = std::vector::size_type;
TextQuery(std::ifstream& );
QueryResult query(const std::string& ) const;
private:
std::shared_ptr > file; //文件内容
std::map > > wm; //词和行号的集合
};
/*把每一行放入text, 存入file(vector), 组成word和行号(set)的映射*/
TextQuery::TextQuery(std::ifstream &is) : file(new std::vector)
{
std::string text;
while (std::getline(is, text)) {
file->push_back(text);
int n = file->size() - 1;
std::istringstream line(text);
std::string word;
while (line >> word) {
auto& lines = wm[word];
if (!lines)
lines.reset(new set);
lines->insert(n);
}
}
}
class QueryResult {
friend std::ostream& print (std::ostream&, const QueryResult& );
public:
using line_no = std::vector::size_type;
QueryResult (std::string s, //查询单词
std::shared_ptr> p, //匹配行号
std::shared_ptr> f) : //输入文件
sought(s), lines(p), file(f) {}
std::set::iterator begin() { return lines->begin(); }
std::set::iterator end() { return lines->end(); }
std::shared_ptr> get_file() { return file; }
private:
std::string sought; //查找字符串
std::shared_ptr> lines; //行号集合
std::shared_ptr> file; //文件集合
};
/*找到指定sought的集合, 返回迭代器, 传入string和set*/
QueryResult TextQuery::query(const std::string& sought) const {
static std::shared_ptr> nodata(new std::set);
auto loc = wm.find(sought);
if (loc == wm.end())
return QueryResult(sought, nodata, file); //没有找到, 不打印
else
return QueryResult(sought, loc->second, file); //按行号打印
};
std::string make_plural (std::size_t ctr, const std::string& word,
const std::string ending)
{
return (ctr > 1) word + ending : word;
}
std::ostream& print(std::ostream& os, const QueryResult &qr){
os << qr.sought << " occurs " << qr.lines->size() << " "
<< make_plural(qr.lines->size(), "time", "s") << std::endl;
for(auto num : *qr.lines)
os << "\t(line " << num+1 << ") " << *(qr.file->begin()+num) << std::endl;
return os;
}
void runQueries (std::ifstream &infile) {
TextQuery tq(infile);
while (true) {
std::cout << "enter word to look for, or q to quit: ";
std::string s;
if ( !(cin>>s) || s == "q" ) break;
print(std::cout, tq.query(s)) << std::endl;
}
}
/*抽象基类, 没有public成员*/
class Query_base {
friend class Query;
protected:
using line_no = TextQuery::line_no;
virtual ~Qu