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- Subject: Re: [ANN] Lua 5.3.0 (rc3) now available
- From: Daurnimator <quae@...>
- Date: Fri, 2 Jan 2015 12:51:32 -0500
On 2 January 2015 at 12:35, Roberto Ierusalimschy
> This code has been like this for more than 10 years. Why did you wait for
> 'rc3' to complain? :-)
I only just tried adding -pedantic to MYCFLAGS
>> To get around this, you need to use this hack: (as seem in dlsym manpage/POSIX):
>> double (*cosine)(double);
>> /* Writing: cosine = (double (*)(double)) dlsym(handle, "cos");
>> would seem more natural, but the C99 standard leaves
>> casting from "void *" to a function pointer undefined.
>> The assignment used below is the POSIX.1-2003 (Technical
>> Corrigendum 1) workaround; see the Rationale for the
>> POSIX specification of dlsym(). */
>> *(void **) (&cosine) = dlsym(handle, "cos");
> This hack is as undefined in C99 as ours,
The rationale from POSIX
> The ISO C standard does not require that pointers to functions can be cast back and forth to pointers to data. Indeed, the ISO C standard does not require that an object of type void * can hold a pointer to a function. Implementations supporting the XSI extension, however, do require that an object of type void * can hold a pointer to a function. The result of converting a pointer to a function into a pointer to another data type (except void *) is still undefined, however. Note that compilers conforming to the ISO C standard are required to generate a warning if a conversion from a void * pointer to a function pointer is attempted as in
> fptr = (int (*)(int))dlsym(handle, "my_function");
> but we can change that if
> it removes the warning.
It does on my PC.