c++ - 检查标准输入是否为空

Question

我搜索了但没有得到这个问题的相关答案，我在 linux 机器上工作，我想检查标准输入流是否包含任何字符，而不从流中删除字符。

Answer 1

您可能想尝试 select()函数，并等待数据进入输入流。

描述:

select() and pselect() allow a program to monitor multiple file descriptors, waiting until one or more of the file descriptors become "ready" for some class of I/O operation (e.g., input possible). A file descriptor is considered ready if it is possible to perform the corresponding I/O operation (e.g., read(2)) without blocking.

在您的情况下，文件描述符将是 stdin

void yourFunction(){
    fd_set fds;
    struct timeval timeout;
    int selectRetVal;

    /* Set time limit you want to WAIT for the fdescriptor to have data, 
       or not( you can set it to ZERO if you want) */
    timeout.tv_sec = 0;
    timeout.tv_usec = 1;

    /* Create a descriptor set containing our remote socket
       (the one that connects with the remote troll at the client side).  */
    FD_ZERO(&fds);
    FD_SET(stdin, &fds);

    selectRetVal = select(sizeof(fds)*8, &fds, NULL, NULL, &timeout);

    if (selectRetVal == -1) {
        /* error occurred in select(),  */
        printf("select failed()\n");
    } else if (selectRetVal == 0) {
        printf("Timeout occurred!!! No data to fetch().\n");
        //do some other stuff
    } else {
        /* The descriptor has data, fetch it. */
        if (FD_ISSET(stdin, &fds)) {
            //do whatever you want with the data
        }
    }
}

希望对您有所帮助。