linux select 阻塞

#include <stdio.h>
#include <stdlib.h>
#include <sys/select.h>
#include <sys/time.h>
#include <unistd.h>

int main() {
    fd_set read_fds;
    struct timeval timeout;

    FD_ZERO(&read_fds);
    FD_SET(STDIN_FILENO, &read_fds);  // 监听标准输入

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

    int ret = select(STDIN_FILENO + 1, &read_fds, NULL, NULL, &timeout);
    if (ret == -1) {
        perror("select error");
        return 1;
    } else if (ret == 0) {
        printf("select timeout\n");
    } else {
        if (FD_ISSET(STDIN_FILENO, &read_fds)) {
            char buffer[1024];
            fgets(buffer, sizeof(buffer), stdin);
            printf("Received input: %s", buffer);
        }
    }

    return 0;
}