Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
499 views
in Technique[技术] by (71.8m points)

c++ - How does void* work as a universal reference type?

From Programming Language Pragmatics, by Scott

For systems programming, or to facilitate the writing of general-purpose con- tainer (collection) objects (lists, stacks, queues, sets, etc.) that hold references to other objects, several languages provide a universal reference type. In C and C++, this type is called void *. In Clu it is called any; in Modula-2, address; in Modula-3, refany; in Java, Object; in C#, object.

In C and C++, how does void * work as a universal reference type?

void * is always only a pointer type, while a universal reference type contains all values, both pointers and nonpointers. So I can't see how void * is a universal reference type.

Thanks.

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Answer

0 votes
by (71.8m points)

A void* pointer will generally hold any pointer that is not a C++ pointer-to-member. It's rather inconvenient in practice, since you need to cast it to another pointer type before you can use it. You also need to convert it to the same pointer type that it was converted from to make the void*, otherwise you risk undefined behavior.

A good example would be the qsort function. It takes a void* pointer as a parameter, meaning it can point to an array of anything. The comparison function you pass to qsort must know how to cast two void* pointers back to the types of the array elements in order to compare them.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

2.1m questions

2.1m answers

60 comments

57.0k users

...