您想的fcntl（）来检查的FD读/写设置：

You want fcntl() to check for read/write settings on the fd:

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

int    r;

r = fcntl(fd, F_GETFL);
if (r == -1)
        /* Error */
if (r & O_RDONLY)
    /* Read Only */
else if (r & O_WRONLY)
    /* Write Only */
else if (r & O_RDWR)
    /* Read/Write */

但是，这是从当套接字不再连接一个单独的问题。如果你已经在使用选择（）或调查（）那么你几乎没有。 调查（）如果您指定将返回状态很好 POLLERR 在事件和的revents 检查它>。

But this is a separate issue from when the socket is no longer connected. If you are already using select() or poll() then you're almost there. poll() will return status nicely if you specify POLLERR in events and check for it in revents.

如果你正在做正常阻塞I / O然后只处理读/因为他们进来写入错误和正常恢复。

If you're doing normal blocking I/O then just handle the read/write errors as they come in and recover gracefully.