netconn_recv的recv_buf字段接收字节大小哪里定义

netconn_recv函数的recv_buf字段接收字节大小是在调用netconn_new函数创建一个新的netconn结构体时指定的。具体来说，可以通过设置netconn结构体的recv_bufsize字段来指定recv_buf的大小，或者使用netconn_set_recvbufsize函数动态设置。默认情况下，recv_bufsize为2048个字节。

相关问题

netconn_recv(conn, &buf);得到的buf怎么得到这些数据struct udp_pcb *upcb, struct pbuf *p, const ip_addr_t *addr, u16_t port

在调用`netconn_recv(conn, &buf)`之后，会将接收到的数据放入`buf`中。如果您使用的是`UDP`协议，您可以通过以下方式获取相关信息：

1. 获取`udp_pcb`结构体指针：

struct udp_pcb *upcb = conn->pcb.udp;

2. 获取`pbuf`结构体指针：

struct pbuf *p;
netbuf_data(buf, (void **)&p, &len);

3. 获取发送方的IP地址和端口：

const ip_addr_t *addr = netbuf_fromaddr(buf);
u16_t port = netbuf_fromport(buf);

其中，`addr`和`port`分别表示发送方的IP地址和端口，`len`表示接收到的数据的长度。

需要注意的是，`netbuf_fromaddr()`返回的是一个指向IP地址的指针，需要使用`ipaddr_ntoa()`函数进行转换成字符串形式。

netconn_recv(udpconn, &recvbuf)接收不到数据

buf, len)

The netconn_recv() function is used to receive incoming data on a UDP connection. It takes three arguments:

1. udpconn: This is the UDP connection on which the data is to be received.

2. buf: This is the buffer where the received data will be stored.

3. len: This is the maximum length of data that can be received in a single call.

The function returns the number of bytes received, or a negative error code if an error occurred. If the return value is zero, it means that the connection was closed by the remote endpoint.

Note that the netconn_recv() function is a blocking call, which means that it will wait until data is available before returning. To avoid blocking indefinitely, it is recommended to use a timeout or a non-blocking mode.