C++中的常见I/O方式

目录
摘要
1. 标准输入输出（Standard I/O）
2. 文件输入输出（File I/O）
3. 字符串流（String Stream）
4. 低级文件I/O（Low-level File I/O）
5. 内存映射文件（Memory-Mapped File I/O）
6. 网络I/O（Network I/O）
服务器端
客户端

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摘要

C++中的输入输出操作（I/O）方式多种多样，从简单的标准I/O到复杂的内存映射文件和网络I/O。每一种的用法都有其特别之处，下面会分别用代码的方式来简单先容一些用法，可以根据自己项目所需来选择符合的I/O方式可以进步我们项目开发的服从。
1. 标准输入输出（Standard I/O）

标准输入输出用于与控制台举行交互。

1. #include <iostream>
2. #include <vector>
3. #include <string>
4. #include <sstream>
5. using namespace std;
7. struct Student {
8.     string name;
9.     int age;
10.     vector<int> grades;
12.     void display() const {
13.         cout << "Name: " << name << ", Age: " << age << ", Grades: ";
14.         for (int grade : grades) {
15.             cout << grade << " ";
16.         }
17.         cout << endl;
18.     }
19. };
21. int main() {
22.     vector<Student> students;
23.     string input;
24.     cout << "Enter student information (name age grades), type 'end' to stop:" << endl;
25.     while (true) {
26.         getline(cin, input);
27.         if (input == "end") break;
29.         istringstream iss(input);
30.         Student student;
31.         iss >> student.name >> student.age;
32.         int grade;
33.         while (iss >> grade) {
34.             student.grades.push_back(grade);
35.         }
36.         students.push_back(student);
37.     }
39.     cout << "Entered students:" << endl;
40.     for (const Student& student : students) {
41.         student.display();
42.     }
44.     return 0;
45. }

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2. 文件输入输出（File I/O）

文件I/O操作允许将数据存储到文件中或从文件中读取。

1. #include <fstream>
2. #include <iostream>
3. #include <vector>
4. #include <string>
5. using namespace std;
7. struct Employee {
8.     string name;
9.     int id;
10.     double salary;
12.     void display() const {
13.         cout << "Name: " << name << ", ID: " << id << ", Salary: " << salary << endl;
14.     }
15. };
17. int main() {
18.     vector<Employee> employees = {
19.         {"Aoteman", 1, 50000},
20.         {"AotemanDaddy", 2, 60000},
21.         {"AotemanMami", 3, 70000}
22.     };
24.     ofstream outFile("employees.dat", ios::binary);
25.     if (!outFile) {
26.         cerr << "Error opening file for writing" << endl;
27.         return 1;
28.     }
29.     for (const Employee& emp : employees) {
30.         outFile.write((char*)&emp, sizeof(Employee));
31.     }
32.     outFile.close();
34.     vector<Employee> readEmployees;
35.     ifstream inFile("employees.dat", ios::binary);
36.     if (!inFile) {
37.         cerr << "Error opening file for reading" << endl;
38.         return 1;
39.     }
40.     Employee emp;
41.     while (inFile.read((char*)&emp, sizeof(Employee))) {
42.         readEmployees.push_back(emp);
43.     }
44.     inFile.close();
46.     cout << "Read employees:" << endl;
47.     for (const Employee& emp : readEmployees) {
48.         emp.display();
49.     }
51.     return 0;
52. }

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3. 字符串流（String Stream）

字符串流用于处置惩罚内存中的字符串流。

1. #include <sstream>
2. #include <iostream>
3. #include <vector>
4. #include <string>
5. using namespace std;
7. struct Product {
8.     string name;
9.     double price;
10.     int quantity;
12.     void display() const {
13.         cout << "Name: " << name << ", Price: " << price << ", Quantity: " << quantity << endl;
14.     }
15. };
17. int main() {
18.     vector<Product> products = {
19.         {"Apple", 999.99, 5},
20.         {"HuaWei", 699.99, 10},
21.         {"SanXing", 299.99, 7}
22.     };
24.     ostringstream oss;
25.     for (const Product& prod : products) {
26.         oss << prod.name << " " << prod.price << " " << prod.quantity << "\n";
27.     }
28.     string productData = oss.str();
29.     cout << "Serialized products:\n" << productData;
31.     vector<Product> parsedProducts;
32.     istringstream iss(productData);
33.     string name;
34.     double price;
35.     int quantity;
36.     while (iss >> name >> price >> quantity) {
37.         parsedProducts.push_back({name, price, quantity});
38.     }
40.     cout << "Parsed products:" << endl;
41.     for (const Product& prod : parsedProducts) {
42.         prod.display();
43.     }
45.     return 0;
46. }

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4. 低级文件I/O（Low-level File I/O）

低级文件I/O使用系统调用来举行文件操作，提供了更高的灵活性和控制力。

1. #include <fcntl.h>
2. #include <unistd.h>
3. #include <iostream>
4. #include <vector>
5. #include <cstring>
6. using namespace std;
8. struct Record {
9.     char name[20];
10.     int value;
12.     void display() const {
13.         cout << "Name: " << name << ", Value: " << value << endl;
14.     }
15. };
17. int main() {
18.     vector<Record> records = {
19.         {"Record1", 100},
20.         {"Record2", 200},
21.         {"Record3", 300}
22.     };
24.     int fd = open("records.dat", O_WRONLY | O_CREAT, 0644);
25.     if (fd == -1) {
26.         cerr << "Error opening file for writing" << endl;
27.         return 1;
28.     }
29.     for (const Record& rec : records) {
30.         write(fd, &rec, sizeof(Record));
31.     }
32.     close(fd);
34.     vector<Record> readRecords;
35.     fd = open("records.dat", O_RDONLY);
36.     if (fd == -1) {
37.         cerr << "Error opening file for reading" << endl;
38.         return 1;
39.     }
40.     Record rec;
41.     while (read(fd, &rec, sizeof(Record)) > 0) {
42.         readRecords.push_back(rec);
43.     }
44.     close(fd);
46.     cout << "Read records:" << endl;
47.     for (const Record& rec : readRecords) {
48.         rec.display();
49.     }
51.     return 0;
52. }

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5. 内存映射文件（Memory-Mapped File I/O）

内存映射文件将文件内容映射到历程的地址空间。

1. #include <sys/mman.h>
2. #include <fcntl.h>
3. #include <unistd.h>
4. #include <iostream>
5. #include <cstring>
6. using namespace std;
8. struct Data {
9.     char text[50];
10.     int number;
12.     void display() const {
13.         cout << "Text: " << text << ", Number: " << number << endl;
14.     }
15. };
17. int main() {
18.     int fd = open("mmapdata.dat", O_RDWR | O_CREAT, 0644);
19.     if (fd == -1) {
20.         cerr << "Error opening file" << endl;
21.         return 1;
22.     }
24.     Data data = {"Memory-mapped file example", 42};
25.     write(fd, &data, sizeof(Data));
27.     size_t filesize = sizeof(Data);
28.     Data *map = static_cast<Data*>(mmap(0, filesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0));
29.     if (map == MAP_FAILED) {
30.         cerr << "Error mapping file" << endl;
31.         close(fd);
32.         return 1;
33.     }
35.     // 修改映射区域内容
36.     strcpy(map->text, "Updated text");
37.     map->number = 99;
39.     // 取消映射
40.     munmap(map, filesize);
41.     close(fd);
43.     // 读取文件内容
44.     fd = open("mmapdata.dat", O_RDONLY);
45.     if (fd == -1) {
46.         cerr << "Error opening file" << endl;
47.         return 1;
48.     }
49.     Data readData;
50.     read(fd, &readData, sizeof(Data));
51.     close(fd);
53.     cout << "Read data:" << endl;
54.     readData.display();
56.     return 0;
57. }

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6. 网络I/O（Network I/O）

网络I/O用于通过网络举行数据传输，涉及到套接字编程。
服务器端

1. #include <sys/socket.h>
2. #include <netinet/in.h>
3. #include <unistd.h>
4. #include <iostream>
5. #include <cstring>
6. using namespace std;
8. int main() {
9.     int server_fd = socket(AF_INET, SOCK_STREAM, 0);
10.     if (server_fd == -1) {
11.         cerr << "Error creating socket" << endl;
12.         return 1;
13.     }
15.     struct sockaddr_in server_addr;
16.     server_addr.sin_family = AF_INET;
17.     server_addr.sin_port = htons(9090);
18.     server_addr.sin_addr.s_addr = INADDR_ANY;
20.     if (bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
21.         cerr << "Error binding socket" << endl;
22.         close(server_fd);
23.         return 1;
24.     }
26.     if (listen(server_fd, 5) == -1) {
27.         cerr << "Error listening on socket" << endl;
28.         close(server_fd);
29.         return 1;
30.     }
32.     cout << "Server listening on port 9090..." << endl;
34.     int client_fd = accept(server_fd, nullptr, nullptr);
35.     if (client_fd == -1) {
36.         cerr << "Error accepting connection" << endl;
37.         close(server_fd);
38.         return 1;
39.     }
41.     char buffer[256];
42.     ssize_t bytesReceived = recv(client_fd, buffer, sizeof(buffer) - 1, 0);
43.     if (bytesReceived == -1) {
44.         cerr << "Error receiving data" << endl;
45.         close(client_fd);
46.         close(server_fd);
47.         return 1;
48.     }
49.     buffer[bytesReceived] = '\0';
50.     cout << "Received from client: " << buffer << endl;
52.     const char *response = "Message received";
53.     send(client_fd, response, strlen(response), 0);
55.     close(client_fd);
56.     close(server_fd);
58.     return 0;
59. }

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客户端

1. #include <sys/socket.h>
2. #include <netinet/in.h>
3. #include <arpa/inet.h>
4. #include <unistd.h>
5. #include <iostream>
6. #include <cstring>
7. using namespace std;
9. int main() {
10.     int sockfd = socket(AF_INET, SOCK_STREAM, 0);
11.     if (sockfd == -1) {
12.         cerr << "Error creating socket" << endl;
13.         return 1;
14.     }
16.     struct sockaddr_in server_addr;
17.     server_addr.sin_family = AF_INET;
18.     server_addr.sin_port = htons(9090);
19.     server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
21.     if (connect(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
22.         cerr << "Error connecting to server" << endl;
23.         close(sockfd);
24.         return 1;
25.     }
27.     const char *msg = "Hello, server!";
28.     send(sockfd, msg, strlen(msg), 0);
30.     char buffer[256];
31.     ssize_t bytesReceived = recv(sockfd, buffer, sizeof(buffer) - 1, 0);
32.     if (bytesReceived == -1) {
33.         cerr << "Error receiving data" << endl;
34.     } else {
35.         buffer[bytesReceived] = '\0';
36.         cout << "Received from server: " << buffer << endl;
37.     }
39.     close(sockfd);
40.     return 0;
41. }

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