c++ primer 学习笔记9--文件输入输出

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书285页，练习8.4

#include <iostream>  #include <fstream>#include <vector>#include <string>using namespace std;int main(){ifstream in("data.txt");if (!in){cerr << "无法打开输入文件" << endl;return -1;}string line;vector<string> words;while (getline(in, line)){words.push_back(line);}in.close();vector<string>::const_iterator it = words.begin();while (it != words.end()){cout << *it << " ";++it;}}

8.6+8.7将输入文件名作为第一个参数，传给main函数，将输出文件名作为第二个参数传给main函数。

#include <iostream>  #include <fstream>#include "Sales_data.h"using namespace std;int main(int argc,char *argv[]){if(argc != 3){cerr << "请给出输入，输出文件名" << endl;return -1;}ifstream in(argv[1]);if (!in){cerr << "无法打开输入文件" << endl;return -1;}ofstream out(argv[2]);if (!out){cerr << "无法打开输出文件" << endl;return -1;}Sales_data total;if (read(in, total)){Sales_data trans;while (read(out, trans)){if (total.isbn() == trans.isbn())total.combine(trans);else{print(out, total) << endl;total = trans;}}print(out, total) << endl;}elsecerr << "No data" << endl;}

练习8.10，将来自一个文件中的行保存在一个vector<string>中，然后使用一个istringstream从vector读取数据元素，每次读取一个单词

#include <iostream>  #include <fstream>#include <sstream>#include <vector>#include <string>using namespace std;int main(int argc,char *argv[]){ifstream in("data.txt");if (!in){cerr << "无法打开输入文件" << endl;return -1;}string line;vector<string> words;while (getline(in, line)){words.push_back(line);}in.close();vector<string>::const_iterator it = words.begin();while (it != words.end()){istringstream line_str(*it);string word;while (line_str >> word){cout << word << " ";++it;}}}

8.11

#include <iostream>  #include <fstream>#include <sstream>#include <vector>#include <string>using namespace std;struct PersonInfo{string name;vector<string> phones;};int main(int argc,char *argv[]){string line, word;vector<PersonInfo> people;istringstream record;while (getline(cin, line)){PersonInfo info;//创建一个保存此数据的对象record.clear();//重复使用字符串流的时候，每次调用clearrecord.str(line);//将记录绑定到刚刚读入的行record >> info.name;//读取名字while (record >> word)//保持{info.phones.push_back(word);}people.push_back(info);}}

8.13

#include <iostream>  #include <fstream>#include <sstream>#include <vector>#include <string>using namespace std;struct PersonInfo{string name;vector<string> phones;};string format(const string &s){ return s; }bool valid(const string &s){////return true;}int main(int argc,char *argv[]){string line, word;vector<PersonInfo> people;istringstream record;if (argc != 2){cerr << "请给出文件名" << endl;return -1;}ifstream in(argv[1]);if (!in){cerr << "无法打开输入文件" << endl;return -1;}while (getline(cin, line)){PersonInfo info;//创建一个保存此数据的对象record.clear();//重复使用字符串流的时候，每次调用clearrecord.str(line);//将记录绑定到刚刚读入的行record >> info.name;//读取名字while (record >> word)//保持{info.phones.push_back(word);}people.push_back(info);}ostringstream os;for (const auto &entry : people){ostringstream formatted, badNums;for (const auto &nums : entry.phones){if (!valid(nums)){badNums << " " << nums;}else{formatted << " " << format(nums);}if (badNums.str().empty()){os << entry.name << " " << formatted.str() << endl;}else{cerr << "input error:" << entry.name << "invalid number(s)" << badNums.str() << endl;}cout << os.str() << endl;}}}

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