eCosPro® Reference Manual
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# tcp_listen()

## Name

tcp_listen() -- Make PCB listen for incoming connections

## Synopsis

`struct tcp_pcb *tcp_listen`(struct tcp_pcb *pcb);

## Description

Commands pcb to start listening for incoming connections. When an incoming connection is accepted, the function specified with the `tcp_accept()` function will be called. pcb must have been bound to a local port with the `tcp_bind()` function.

## Return value

The `tcp_listen()` function returns a new connection identifier, and the one passed as an argument to the function will be deallocated. The reason for this behavior is that less memory is needed for a connection that is listening, so `tcp_listen()` will reclaim the memory needed for the original connection and allocate a new smaller memory block for the listening connection.

`tcp_listen()` may return `NULL` if no memory was available for the listening connection. If so, the memory associated with pcb will not be deallocated.

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