David Smart

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8 years, 9 months ago.

callback to class - member function - can't quite make it work...

Hi C++ experts, I'm struggling. I found examples, none quite match my needs, so tried to derive a solution - but to no success.

The comments below reflect the compiler output.

#include "mbed.h"

class Callback {
    public:   
        template <typename T> Callback(T * tptr, int (T::*mptr)(char * p), size_t allocsize) {
            m_size = allocsize;
            m_fp.attach(tptr, mptr);  
            // No instance of overloaded function mbed::FunctionPointerArg1::attach[with R=void] 
            // matches the argument list m_fp.attach(tptr, mptr);
        }
        void doit(void) {
            int x = 3;
            printf("size is %d\r\n", m_size);
            x = m_fp.call("hello");
            // Too many arguments in function call x = m_fp.call("hello");
            // A value of type "void" cannot be assigned to an entity of type int x = m_fp.call("hello");
            printf("callback returned %d\r\n", x);
        }
    private:
        size_t m_size;
        FunctionPointer m_fp;
};

class Worker {
    public:
        Worker() { }
        int Process(char * p) {
            printf("Process(%s)\r\n", p);
            return 7;
        }
};


int main() {
    Worker wk;
    Callback cb(&wk, &Worker::Process, 75);
    cb.doit();    
}

Is it that "FunctionPointer" is restricted and it cannot match the signature of "int function(char *)"?

1 Answer

Andy A
8 years, 9 months ago.

FunctionPointer only takes functions of type void function (void) There is an FPointer class https://developer.mbed.org/cookbook/FPointer that takes functions of type uint32_t function (uint32_t) which should do what you need if you cast the char* to a uint32_t. Or you could just create your own callback, it's not that complicated to do.

Accepted Answer