将文件描述符设置为非阻塞，可以采用fcntl接口

 #include <unistd.h>
 #include <fcntl.h>

 int fcntl(int fd, int cmd, ... /* arg */ );

一下采用F_GETFD，先获取文件描述符的标记，然后再添加非阻塞选项

#include<iostream>
#include<unistd.h>
#include<fcntl.h>
#include<cstdio>
#include<cstring>
#include<cerrno>

using namespace std;

void SetNOBlock(int fd)
{
    int fl = fcntl(fd, F_GETFD);	//获取文件描述符标记
    if(fl < 0)  //获取失败
    {
        perror("fcntl");
        return;
    }
    fcntl(fd, F_SETFL, fl | O_NONBLOCK);	//添加非阻塞选项
    cout << "set " << fd << " non block success" << endl;
}

int main()
{
    char buffer[1024];
    SetNOBlock(0);
    sleep(1);

    while(true)
    {
        // printf("Please Enter: ");
        // fflush(stdout);

        ssize_t n = read(0, buffer, sizeof(buffer)-1);
        if(n > 0)
        {
            buffer[n-1] = 0;
            cout << "echo: " << buffer << endl;
        }
        else if(n == 0)
        {
            cout << "read done" << endl;
            break;
        }
        else
        {
            if(errno == EWOULDBLOCK)
            {
                cout << "0 fd data not ready, please try again" << endl;
                sleep(1);
            }
            else
            {
                cerr << "read error, fd = " << n << ", erron code: " << errno << " error str:" << strerror(errno) << endl;
                break;
            }
        }
    }
    return 0;
}

当read的错误码为11(EWOULDBLOCK)时，表示当前文件描述符数据没有就绪