3 ms·

It’s not a warning, it’s a compile time error and I am not even using -Wall -Werror I also believe there are platforms where a function pointer and a data poin

It’s not a warning, it’s a compile time error and I am not even using -Wall -Werror I also believe there are platforms where a function pointer and a data pointer are not the same but idk about such esoteric platforms first hand (seems Itanium had that: https://stackoverflow.com/questions/36645660/why-cant-i-cast-a-function-pointer-to-void https://stackoverflow.com/questions/36645660/why-cant-i-cast...) Though my point was only that this code will not compile as is with whatever clang Apple ships* I am not really sure how to get it to compile tbqh Some further research ( https://www.kdab.com/how-to-cast-a-function-pointer-to-a-void/ https://www.kdab.com/how-to-cast-a-function-pointer-to-a-voi...) suggest it should be done like so: > auto fptr = &f; void a = reinterpret_cast<void &>(fptr); edit: I tried with GCC 15 and that compiled successfully

comex 1y ago
It should just be res.fn = (void *)fn; `res.fn` is of type `void *`, so that's what the code should be casting to. Casting to `func0Ptr` there seems to just be a mistake. Some compilers may allow the resulting function pointer to then implicitly convert to `void *`, but it's not valid in standard C++, hence the error. Separately from that, if you enable -Wpedantic, you can get a warning for conversions between function and data pointers even if they do use an explicit cast, but that's not the default.
gpderetta 1y ago
FWIW, POSIX practically requires void otr and function otr inter-convertibility hence the support from GCC.
- wahern 1y ago
  Not practically, but literally: Note that conversion from a void * pointer to a function pointer as in: fptr = (int (*)(int))dlsym(handle, "my_function"); is not defined by the ISO C standard. This standard requires this conversion to work correctly on conforming implementations.
  - gpderetta 1y ago
    I remembered the dlsym requirement, I wasn't sure it was de-jure.

comex 1y ago

It should just be res.fn = (void *)fn; `res.fn` is of type `void *`, so that's what the code should be casting to. Casting to `func0Ptr` there seems to just be a mistake. Some compilers may allow the resulting function pointer to then implicitly convert to `void *`, but it's not valid in standard C++, hence the error. Separately from that, if you enable -Wpedantic, you can get a warning for conversions between function and data pointers even if they do use an explicit cast, but that's not the default.

gpderetta 1y ago

FWIW, POSIX practically requires void otr and function otr inter-convertibility hence the support from GCC.

wahern 1y ago
Not practically, but literally: Note that conversion from a void * pointer to a function pointer as in: fptr = (int (*)(int))dlsym(handle, "my_function"); is not defined by the ISO C standard. This standard requires this conversion to work correctly on conforming implementations.
- gpderetta 1y ago
  I remembered the dlsym requirement, I wasn't sure it was de-jure.