Compiler warning for cast in Ticker code

[Niek]

Sample code:

#include <Ticker.h>

void testFn(unsigned char i) {}

void setup() {
  Ticker t;
  unsigned char i = 1;
  t.once_ms(100, testFn, i);
}

I get this warning when compiling the latest git version:

libraries/Ticker/Ticker.h: In instantiation of 'void Ticker::once_ms(uint32_t, void (*)(TArg), TArg) [with TArg = unsigned char; uint32_t = unsigned int]':

libraries/Ticker/Ticker.h:110:94: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
   _attach_ms(milliseconds, false, reinterpret_cast<callback_with_arg_t>(callback), (void*)arg);

It originates from this line of code (changed in commit 7910121):

Arduino/libraries/Ticker/Ticker.h

Line 110 in 48ace77

_attach_ms(milliseconds, false, reinterpret_cast<callback_with_arg_t>(callback), (void*)arg);

It seems that it's caused by the (void*) cast in the last parameter.

[earlephilhower]

You have a problem in your code.

The function signature for a callback is void (cb)(void *data), not void (cb)(unsigned char). Change the callback to the proper signature and then, inside the function, convert from void* to the unsigned char with something like below.

void testFn(void *cbData) {
    unsigned char i = static_cast<unsigned char>(cbData);
   ....
}

[Niek]

Are you saying the callback function can't take other types as argument, as explained in the sample? https://github.com/esp8266/Arduino/blob/master/libraries/Ticker/examples/TickerParameter/TickerParameter.ino
Or is it the unsigned part that makes it problematic?
By the way the code works fine in core 2.5.2.

[earlephilhower]

Actually, I'm mistaken and you're right. The template is supposed to handle that from how I read it:

        template<typename TArg>
        void once_ms(uint32_t milliseconds, void (*callback)(TArg), TArg arg)

The (void*) in the template body looks to be incorrect and should be able to do promotion to a pointer silently, w/o error. We need a fix and a test case that hits this.

[Niek]

Thanks! I can confirm it's fixed in 8c37601 - closing this issue