在 2019/12/18 上午12:30, Vincent Lefevre 写道: > On 2019-12-17 16:27:28 +0100, Manfred wrote: >> On 12/17/2019 2:22 PM, Segher Boessenkool wrote: >>> Is there *any* portable way to print function pointers? Other than >>> accessing it as bytes :-) >> >> n1570 section 6.3.2.3 p6 says "Any pointer type may be converted to an >> integer type. Except as previously specified, the result is >> implementation-defined. ..." >> >> It says implementation-defined, not undefined, > There's an enormous number of implementation-defined things, which people kind of rely on to write 'portable code': 0. Conversion a value from `unsigned int` to `signed char` which doesn't fit in it yields an implementation-defined result. [C++14 now requires 2's complement, which is required by GCC.] 1. Shifting a negative integer to the right yields an impl-def result. Shifting a negative integer to the left is undefined behavior. [Ditto.] 2. Calling `fflush()` on an input stream results in undefined behavior. [The behavior is defined by POSIX 2008.] 3. Comparing two pointers that do not point to elements or past-the-end position of the same array, using one of <, >, <= or >= operators, results in undefined behavior. [C++ says the result is unspecified.] So how can you write 'portable code' without regard to these facts? In addition, even if it could be 'portable' to have standard casts between `void*` and function pointers, the `%p` specifier of `printf()` is still impl-def. So how can you make such combination more 'portable'? -- Best regards, LH_Mouse