第八章 IO库
2024-08-28 21:56:43
8.1&&8.2
#include <iostream>
#include <vector>
#include <string> using namespace std; istream &func(istream &is)
{
int val;
while (is >> val && !is.eof()) {
cout << val << endl;
}
is.clear(); //复位所有错误标志位
} int main()
{
func(cin);
return ;
}
8.3
读取类型不匹配；遇到文件结束符EOF；IO流错误
8.4
#include <iostream>
#include <fstream>
#include <vector>
#include <string> using namespace std; int main()
{
vector<string> vec;
string ifile = "data.txt", ss; //需在本文件夹下有data.txt这个文件
ifstream in(ifile);
while(getline(in, ss)) {
vec.push_back(ss);
}
in.close();
for (auto i : vec)
cout << i << endl;
return ;
}
8.5
#include <iostream>
#include <fstream>
#include <vector>
#include <string> using namespace std; int main()
{
vector<string> vec;
string ifile = "data.txt", ss; //需在本文件夹下有data.txt这个文件
ifstream in(ifile);
while(in >> ss) { //改动处
vec.push_back(ss);
}
in.close();
for (auto i : vec)
cout << i << endl;
return ;
}
8.6
#include <iostream>
#include <fstream>
#include <vector>
#include <string> using namespace std; struct Sales_data {
string bookNo; //书的ISBN
unsigned units_sold = ; //售出的本数
double revenue = 0.0; //销售额
Sales_data& combine(const Sales_data &);
string isbn() { return bookNo; }
}; Sales_data &Sales_data::combine(const Sales_data &rhs)
{
units_sold += rhs.units_sold;
revenue += rhs.revenue;
return *this;
} istream &read(istream &is, Sales_data &item)
{
is >> item.bookNo >> item.units_sold >> item.revenue;
return is;
} ostream &print(ostream &os, const Sales_data &item)
{
os << item.bookNo << " " << item.units_sold << " " << item.revenue;
return os;
} Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
{
Sales_data sum = lhs;
sum.combine(rhs);
return sum;
} int main(int argc, char *argv[])
{
if (argc != ) {
cerr<< "Please give the file name."<<endl;
return -;
}
ifstream in(argv[]);
if (!in) {
cerr<<"Can't open the file."<<endl;
return -;
}
Sales_data total;
if (read(in, total)) {
Sales_data trans;
while (read(in, trans)) {
if (total.isbn() == trans.isbn()) total = add(total, trans);
else {
print(cout, total);
cout << endl;
total = trans; //结构体赋值很方便
}
}
cout << total.bookNo << " " << total.units_sold << " " << total.revenue << endl;
}
else {
cerr << "No data?!" << endl;
return -;
}
return ;
}
文件名（book.txt）通过参数传给main函数：
8.7
#include <iostream>
#include <fstream>
#include <vector>
#include <string> using namespace std; struct Sales_data {
string bookNo; //书的ISBN
unsigned units_sold = ; //售出的本数
double revenue = 0.0; //销售额
Sales_data& combine(const Sales_data &);
string isbn() { return bookNo; }
}; Sales_data &Sales_data::combine(const Sales_data &rhs)
{
units_sold += rhs.units_sold;
revenue += rhs.revenue;
return *this;
} istream &read(istream &is, Sales_data &item)
{
is >> item.bookNo >> item.units_sold >> item.revenue;
return is;
} ostream &print(ostream &os, const Sales_data &item)
{
os << item.bookNo << " " << item.units_sold << " " << item.revenue;
return os;
} Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
{
Sales_data sum = lhs;
sum.combine(rhs);
return sum;
} int main(int argc, char *argv[])
{
if (argc != ) {
cerr<< "Please give the input file name and output file name."<<endl;
return -;
}
ifstream in(argv[]);
ofstream out(argv[]);
if (!in) {
cerr<<"Can't open the file."<<endl;
return -;
}
if (!out) {
cerr<<"can't open output file."<<endl;
return -;
}
Sales_data total;
if (read(in, total)) {
Sales_data trans;
while (read(in, trans)) {
if (total.isbn() == trans.isbn()) total = add(total, trans);
else {
print(out, total) << endl; //输出到指定文件中
total = trans;
}
}
print(out, total) << endl;
}
else {
cerr << "No data?!" << endl;
return -;
}
return ;
}
将上一题输出的内容输出到文件book1.txt中：
8.8
#include <iostream>
#include <fstream>
#include <vector>
#include <string> using namespace std; struct Sales_data {
string bookNo; //书的ISBN
unsigned units_sold = ; //售出的本数
double revenue = 0.0; //销售额
Sales_data& combine(const Sales_data &);
string isbn() { return bookNo; }
}; Sales_data &Sales_data::combine(const Sales_data &rhs)
{
units_sold += rhs.units_sold;
revenue += rhs.revenue;
return *this;
} istream &read(istream &is, Sales_data &item)
{
is >> item.bookNo >> item.units_sold >> item.revenue;
return is;
} ostream &print(ostream &os, const Sales_data &item)
{
os << item.bookNo << " " << item.units_sold << " " << item.revenue;
return os;
} Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
{
Sales_data sum = lhs;
sum.combine(rhs);
return sum;
} int main(int argc, char *argv[])
{
if (argc != ) {
cerr<< "Please give the input file name and output file name."<<endl;
return -;
}
ifstream in(argv[]);
ofstream out(argv[], ofstream::app); //唯一改变之处
if (!in) {
cerr<<"Can't open the file."<<endl;
return -;
}
if (!out) {
cerr<<"can't open output file."<<endl;
return -;
}
Sales_data total;
if (read(in, total)) {
Sales_data trans;
while (read(in, trans)) {
if (total.isbn() == trans.isbn()) total = add(total, trans);
else {
print(out, total) << endl;
total = trans;
}
}
print(out, total) << endl;
}
else {
cerr << "No data?!" << endl;
return -;
}
return ;
}
8.9
#include <iostream>
#include <vector>
#include <string>
#include <sstream> using namespace std; int main()
{
string line, word;
while(getline(cin, line)) {
istringstream in(line);
while (in >> word)
cout << word << endl;
}
return ;
}
8.10
#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <sstream> using namespace std; int main()
{
vector<string> vec;
string line, word;
ifstream input("data.txt");
while(getline(input, line)) {
vec.push_back(line);
}
for (auto i : vec) {
istringstream in(i);
while (in >> word) {
cout << word << endl;
}
}
return ;
}
8.11
#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <sstream> using namespace std; struct PersonInfo {
string name;
vector<string> phones;
}; int main()
{
string line, word;
vector<PersonInfo> people;
istringstream record; //定义在循环之外
while (getline(cin,line)) {
PersonInfo info;
record.clear(); //每次要解除上次绑定的string对象
record.str(line);
record >> info.name;
while (record >> word)
info.phones.push_back(word);
people.push_back(info);
}
return ;
}
8.12
因为此时我们需要其中的成员皆可被访问，所以 PersonInfo 是一个聚合类，不能在内部进行初始化
8.13
#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <sstream> using namespace std; struct PersonInfo {
string name;
vector<string> phones;
}; int main()
{
ifstream in("data.txt"); //从文件读取
string line, word;
vector<PersonInfo> people;
istringstream record;
while (getline(in,line)) { //in为文件输入流
PersonInfo info;
record.clear();
record.str(line);
record >> info.name;
while (record >> word)
info.phones.push_back(word);
people.push_back(info);
}
return ;
}
8.14
这两条语句分别适用范围for语句枚举people中所有项和每项的phones中的所有项。
使用const表明在循环中不会改变这些项的值；
使用auto是请求编译器依据vector元素类型来推断出entry和nums的类型，既简化代码又避免出错；
使用引用的原因是，people和phones的元素分别是结构对象和字符串对象，使用引用即可避免对象拷贝。
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