How do C++ functions handle network events in network programming?

The method of using the select() function to handle network events in C is as follows: Use fd_set to declare a set of file descriptors, and initialize them to set the timeout. Use the select() function to monitor the event of the file descriptor. Check the return value of select(): -1 represents an error, 0 represents a timeout, and a positive value represents an event. Process events (such as receiving data) based on the contents of the file descriptor collection.

C function Handling network events

In network programming, event handling is crucial, allowing the program to respond to network activities, such as receiving data, establishing connections, or handling errors.

There are many ways to handle network events in C, the most common of which is to use the select() function. The select() function allows a program to monitor multiple file descriptors (including sockets) and wait for an event to occur on any one of them.

The syntax of the select() function is as follows:

int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
            struct timeval *timeout);

Among them:

• ##nfds: The maximum number to be monitored Number of file descriptors.
• readfds: The set of file descriptors to be monitored for readability.
• writefds: The set of file descriptors to be monitored for writeability.
• exceptfds: A collection of file descriptors to monitor for exception events.
• timeout: Pointer to the timeval structure, specifying the timeout.

Practical case: Use the select() function to process network events

The following is an example of a C function that handles network events:

#include <sys/select.h>
#include <cstdio>

void handle_network_events(int sockfd) {
  fd_set readfds;
  FD_ZERO(&readfds);
  FD_SET(sockfd, &readfds);

  struct timeval timeout;
  timeout.tv_sec = 5;
  timeout.tv_usec = 0;

  int nfds = select(sockfd + 1, &readfds, NULL, NULL, &timeout);

  if (nfds == -1) {
    perror("select");
  } else if (nfds == 0) {
    printf("Timeout!\n");
  } else {
    if (FD_ISSET(sockfd, &readfds)) {
      // 处理来自 sockfd 的数据
      char buffer[1024];
      int nbytes = recv(sockfd, buffer, sizeof(buffer), 0);
      if (nbytes > 0) {
        printf("Received data: %s\n", buffer);
      }
    }
  }
}

In the above example, the handle_network_events() function monitors readable events from sockfd using the select() function. If data is received within 5 seconds, the function prints the received data. Otherwise, the function times out and prints a message.

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