p.a 和 p->a 有什么区别，其中 p 是指针? [英] what's the difference about p.a and p->a where p is pointer?

问题描述

p.a 和 p->a 有什么区别，其中 p 是指针吗?或者他们只是一回事.

Is there any difference about p.a and p->a where p is pointer? or they are just same thing.

推荐答案

. 运算符实际上是结构成员访问的运算符.

The . operator is actually the operator for structure member access.

struct Foo
{
    int bar;
    int baz;
} aFoo;

aFoo.bar = 3;

如果您有一个指向结构的指针，(非常常见)您可以使用指针解引用和 . 运算符访问其成员.

If you have a pointer to a struct, (very common) you can access its members using pointer dereferencing and the . operator.

struct Foo *p;
p = &aFoo;

(*p).baz = 4;

需要括号是因为 . 比 * 具有更高的优先级.上面取消引用某个结构的成员是非常常见的，因此 -> 被引入作为速记.

The parentheses are needed because . has higher precendence than *. The above dereferencing a member of a structure pointed to by something is extremely common, so -> was introduced as a shorthand.

p->baz = 4; // identical to (*p).baz = 4

如果 p 是一个指针，你永远不会在普通 C 中看到 p.anything ，至少在任何编译器中都不会看到.然而，它在 Objective-C 中用于表示属性访问，这是 IMO 的错误.

If p is a pointer, you never see p.anything in plain C, at least not in anything that compiles. However, it is used to denote property access in Objective-C which was a mistake IMO.

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