[MaxBarraclough]

Thanks for your answers. A related question: this article [0] appears to single out memcpy and memmove as being special regarding effective type. Is it accurate? It seems to be at odds with your suggestion that there's nothing stopping me writing my own memcpy provided I'm careful to use the right types.

[0] https://en.cppreference.com/w/c/language/object#Effective_ty...

[AaronBallman]

I think that may be inaccurate -- IIRC, in C, you can do type punning via a union but not memcpy, and in C++ you can do type punning via memcpy but not a union and this incompatibility drives me nuts because it makes inline functions in a header file shared between C and C++ really messy. (Moral of the story: don't pun types.)

[pascal_cuoq]

The C standard also allows to use memcpy to do type punning:

    If a value is copied into an object having no declared type using memcpy or memmove,
    or is copied as an array of character type, then the effective type of the modified
    object for that access and for subsequent accesses that do not modify the value is
    the effective type of the object from which the value is copied, if it has one

Simply memcpy into a variable (as opposed to dynamically allocated memory).

https://port70.net/~nsz/c/c11/n1570.html#6.5p6

[AaronBallman]

I must be remembering incorrectly then, thank you!

[msebor]

memcpy and memmove aren't special. The part that discusses the copying of allocated objects is 6.5, p6, quoted below:

The effective type of an object for an access to its stored value is the declared type of the object, if any. If a value is stored into an object having no declared type through an lvalue having a type that is not a character type, then the type of the lvalue becomes the effective type of the object for that access and for subsequent accesses that do not modify the stored value. If a value is copied into an object having no declared type using memcpy or memmove, or is copied as an array of character type, then the effective type of the modified object for that access and for subsequent accesses that do not modify the value is the effective type of the object from which the value is opied, if it has one. For all other accesses to an object having no declared type, the effective type of the object is simply the type of the lvalue used for the access.

[MaxBarraclough]

I see, so in short the article is failing to reflect this excerpt: or is copied as an array of character type. Thanks again.

[flatfinger]

Has there ever been any consensus as to what that "...or is copied as an array of character type..." text is supposed to mean, or what sort of hoops must be jumped through for a strictly conforming program to generate an object whose bit pattern matches another without copying the effective type thereof?