- Using Lambda functions for C callbacks
- Simplifies static C++ functions to allowing C to call a C++ functions.
- using GCC init to invoke C functions from C++ initialization.
- One issue in creating projects is how to control or startup threads, init code etc in the proper order without #include every function.
Lambda Functions for C callbacks
lwIP has an asynchronous interface allowing the programmer not to create a thread to wait on socket events, all of the events occur within lwIP worker thread. Using the same thread alleviates locking
err_t tcp_connect (struct tcp_pcb *pcb, const ip_addr_t *ipaddr,
u16_t port, tcp_connected_fn connected);
The above function starts the TCP connection with the IP address in the function. So, function requires a C callback function.
err = tcp_connect(m_conn, &ipaddr, PORT, (void *arg, struct tcp_pcb *tpcb, err_t err) -> err_t
class *pToClass = reinterpret_cast<class *>(args));
return pToClass->connect(tpcb, err);
From the code above, a lambda is used without any capture arguments, this allows the lambda to be callable from C. So, now the connect function can also be a protected function. So, no static function needs to be declared.
Using C++ constructor to invoke a C function before main
Here is a simple function:
static void _startUpUdpServices(void) __attribute__((constructor (102)));
regStartUpFunction(StartUpPriority::_6, "udpServices", (startUpFunctor_t)startUpUDPServices);
The __attribute__((constructor (102))); Puts the function in the .init section and orders it to be at 102. So _startUpUdpServices function will be called before main. This makes it easy to register a system without calling the function. nothing is worse then spegitti code to debug. Now, it is possible to order using higher numbers. I took a little more time and create anoterh class to register function and order them.
If you have any questions let me know...