chapter9.md

第9章 字符串

• C++字符串是基于basic_string模板类的。

    typedef basic_string<char, char_traits<char>, allocator<char> > string;
    typedef basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> > wstring;
    typedef basic_string<char16_t, char_traits<char16_t>, allocator<char16_t> > u16string;
    typedef basic_string<char32_t, char_traits<char32_t>, allocator<char32_t> > u32string;
  

• 字符串应用

    #include <iostream>
    #include <fstream>
    #include <string>
    #include <vector>
    
    using namespace std;
    
    class header_body
    {
    	string body;
    public:
    	header_body() = default;
    	header_body(const string& b) : body(b) {}
    	string get_body() const { return body; }
    	vector<pair<string, string>> subitems() {
    		vector<pair<string, string>> subitems;
    		if (body.find(";") == body.npos) return subitems;
    		size_t start = 0;
    		size_t end = start;
    		while (end != body.npos) {
    			while (start != body.length() && isspace(body[start])) {
    				start++;
    			}
    			if (start == body.length()) break;
    
    			string name = "";
    			string value = "";
    			size_t eq = body.find('=', start);
    			end = body.find(';', start);
    
    			if (eq == body.npos) {
    				if (end == body.npos)
    					name = body.substr(start);
    				else
    					name = body.substr(start, end - start);
    			}
    			else {
    				if (end == body.npos) {
    					name = body.substr(start, eq - start);
    					value = body.substr(eq + 1);
    				}
    				else {
    					if (eq < end) {
    						name = body.substr(start, eq - start);
    						value = body.substr(eq + 1, end - eq -1);
    					}
    					else {
    						name = body.substr(start, end - start);
    					}
    				}
    			}
    			subitems.push_back(make_pair(name, value));
    			start = end + 1;
    		}
    		return subitems;
    	}
    };
    
    class email
    {
    	using iter = vector<pair<string, header_body>>::iterator;
    	vector<pair<string, header_body>> headers;
    	string body;
    public:
    	email() : body("") {}
    
    	//访问器
    	string get_body() const { return body; }
    	string get_headers() const {
    		string all = "";
    		for (auto a : headers) {
    			all += a.first + ": " + a.second.get_body();
    			all += "\n";
    		}
    		return all;
    	};
    	iter begin() { return headers.begin(); }
    	iter end() { return headers.end(); }
    
    	//第二阶段构造
    	void parse(istream& fin);
    private:
    	void process_headers(const vector<string>& lines);
    
    };
    
    void email::parse(istream& fin) {
    	string line;
    	vector<string> headerLines;
    	while (getline(fin, line)) {
    		if (line.empty()) {
    			break;
    		}
    		headerLines.push_back(line);
    	}
    
    	process_headers(headerLines);
    	while (getline(fin, line)) {
    		if (line.empty()) 
    			body.append("\n");
    		else
    			body.append(line);
    	}
    }
    
    void email::process_headers(const vector<string>& lines) {
    	string header = "";
    	string body = "";
    	for (string line : lines) {
    		if (isspace(line[0])) {
    			body.append(line);
    		}
    		else {
    			if (!header.empty()) {
    				headers.push_back(make_pair(header, body));
    				header.clear();
    				body.clear();
    			}
    
    			size_t pos = line.find(":");
    			header = line.substr(0, pos);
    			pos++;
    			while (isspace(line[pos])) pos++;
    			body = line.substr(pos);
    		}
    	}
    
    	if (!header.empty()) {
    		headers.push_back(make_pair(header, body));
    	}
    }
    
    void usage()
    {
    	cout << "usage: emlai_paser file" << endl;
    }
    
    int main(int argc, char* argv[])
    {
    	if (argc <= 1) {
    		usage();
    		return 1;
    	}
    
    	ifstream stm;
    	stm.open(argv[1], ios_base::in);
    	if (!stm.is_open()) {
    		usage();
    		cout << "cannot open " << argv[1] << "\n";
    		return 1;
    	}
    
    	email eml;
    	eml.parse(stm);
    	//cout << "get_headers"<< "\n" << eml.get_headers() << "\n";
    	for (auto header : eml) {
    		cout << header.first << " : ";
    		vector<pair<string, string>> subItems = header.second.subitems();
    		if (subItems.size() == 0) {
    			cout << header.second.get_body() << "\n";
    		}
    		else {
    			cout << "\n";
    			for (auto sub : subItems) {
    				cout << " " << sub.first;
    				if (!sub.second.empty())
    					cout << " = " << sub.second;
    				cout << "\n";
    			}
    		}
    	}
    	cout << "get_body" << "\n" << eml.get_body() << "\n";
    	return 0;
    }