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使用 errdefer 清理失败状态

仅在发生失败时撤销已执行的操作。

使用 errdefer 清理失败状态 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。

Cleanup Only on Failure

Sometimes you must undo work when an operation fails, but keep it when it succeeds. That precise case is what errdefer is for.

Meet errdefer

An errdefer schedules code to run as the scope exits, but only when the function returns an error from that point onward.

errdefer allocator.free(buffer);

defer Always, errdefer on Error

A defer runs no matter how the scope ends. An errdefer runs only on the error path, so success skips it entirely.

Free a Half-Built Result

Allocate, then errdefer the free. If a later step fails the buffer is released; if all steps pass you keep and return it.

const buf = try allocator.alloc(u8, n);
errdefer allocator.free(buf);
try fill(buf);

Order Mirrors Allocation

Place each errdefer right after the matching acquire. On failure they run in reverse, unwinding resources in a safe order.

const a = try open();
errdefer a.close();
const b = try open();
errdefer b.close();

Success Keeps Your Work

When the function returns a value instead of an error, every errdefer is skipped. The caller receives the fully built result.

return buf;

Trigger Point Matters

An errdefer only guards errors that happen after it is registered. Errors before that line cannot run it, so place it early.

Capture the Error

You can capture the error in an errdefer to inspect it during cleanup, for example to log which failure triggered the rollback.

errdefer |e| std.debug.print("failed: {}\n", .{e});

Builds Leak-Free Constructors

Functions that allocate then might fail use errdefer to stay leak-free. Partial work is undone automatically on any error.

Combine with try

Each try may exit early on error. With an errdefer registered, that early exit still triggers your cleanup before unwinding.

const x = try step();
errdefer rollback(x);
_ = try next(x);

The Right Tool for Rollback

Use errdefer when cleanup should happen only if things go wrong. It turns error-path resource management into a single clear line.

Quick Check

You allocate a buffer, then a later step may fail. You want it freed only on failure. What do you use?

Recap

You used errdefer to undo partial work on the error path, placed it right after each acquire, and kept successful results intact. ✅

常见问题解答

「使用 errdefer 清理失败状态」课时是免费的吗？

是的 — 「使用 errdefer 清理失败状态」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。

「使用 errdefer 清理失败状态」这节课中我会学到什么？

仅在发生失败时撤销已执行的操作。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。

「使用 errdefer 清理失败状态」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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