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可选指针与 ?*T

将指针与可选性结合起来。

可选指针与 ?*T 是 CoddyKit 上的免费 Zig Academy 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Zig Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Zig Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Pointers Can Be Optional Too

A pointer normally must always aim at a valid value. Make it optional and it gains a legitimate way to mean nothing yet.

The ?*T Shape

The type ?*T reads as: an optional pointer to a T. It either points at a real value or holds null.

var node: ?*Node = null;

A Safe Null Pointer

This is Zig answer to C null pointers. The pointer can be absent, but the optional forces you to check before dereferencing.

Unwrap Before You Follow

You cannot dereference a ?*T directly. First unwrap it with if or orelse to get the plain pointer underneath.

if (node) |p| {
    use(p.*);
}

Capture Gives a Real Pointer

Inside the if capture the name is a plain *Node, ready to dereference with .* like any non-optional pointer.

if (head) |p| {
    const value = p.*;
}

Great for Linked Structures

Optional pointers shine in linked lists and trees, where a next or child field is null at the end of the chain.

const Node = struct { next: ?*Node };

Null Marks the End

When you walk a list, a next field of null cleanly signals that you have reached the final node and should stop.

Zig Packs the Tag Away

For pointers, Zig stores the null state in the pointer value itself, so a ?*T takes no extra space over a plain pointer.

Const Optional Pointers

You can combine read-only and optional: ?*const T is an optional pointer through which you may read but never write.

var view: ?*const u8 = null;

Still No Surprise Crashes

Because the type says it might be null, the compiler will not let you forget the check, unlike a raw C pointer dereference.

Walking a Chain

A while loop that captures each optional next pointer is the idiomatic way to traverse a list until null appears.

while (cur) |n| {
    cur = n.next;
}

Quick Check

What does the type ?*Node describe?

Recap

You learned ?*T: a safe, optional pointer. Unwrap it before dereferencing, and let null mark the end of linked structures. 🔗

常见问题解答

「可选指针与 ?*T」课时是免费的吗？

是的 — 「可选指针与 ?*T」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Zig Academy 课程的其余内容，请升级到 CoddyKit PRO。 Zig Academy 课程共包含 4 节课。

「可选指针与 ?*T」这节课中我会学到什么？

将指针与可选性结合起来。你通过在浏览器中直接运行的动手代码来练习 Zig Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Zig Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Zig Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 3 节课，共 4 节。

「可选指针与 ?*T」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Zig Academy 课中编写并运行代码吗？

能。每节 Zig Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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