[英]Meaning of adding 1 on socket file descriptor in select function when using linux socket
What is the meaning of adding 1 on socket file descriptor when using in select function?在select函数中使用时socket文件描述符加1是什么意思?
I create socket file descriptor like below,我创建了如下的套接字文件描述符,
int sock_file_descriptor;
sock_file_descriptor = socket(AF_INET, SOCK_DGRAM, 0);
and use it in select function like below,并在如下所示的选择功能中使用它,
result = select(sock_file_descriptor+1, &readfd, NULL, NULL, 0);
What is the meaning of +1 in select function? select函数中+1是什么意思? It even does not work when I remove the calculation adding the value.
当我删除添加值的计算时,它甚至不起作用。
Thanks in advance.提前致谢。
RTFM! RTFM! The first parameter of
select
is the number of file descriptors to considere: select
的第一个参数是要考虑的文件描述符的数量:
The nfds argument specifies the range of descriptors to be tested.
nfds 参数指定要测试的描述符的范围。 The first nfds descriptors shall be checked in each set;
应在每个集合中检查第一个 nfds 描述符; that is, the descriptors from zero through nfds-1 in the descriptor sets shall be examined.
即,应检查描述符集中从 0 到 nfds-1 的描述符。
Here is an example of use:下面是一个使用示例:
// create socket
int sock_file_descriptor;
sock_file_descriptor = socket(AF_INET, SOCK_DGRAM, 0);
// initialize the read fd_set
fd_set read;
FD_ZERO(&read);
FD_SET(sock_file_descriptor, &read);
// ok we can select
result = select(sock_file_descriptor+1, &readfd, NULL, NULL, 0);
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