krahets/hello-algo · error

队列为空

Error message

队列为空

What it means

This panic is raised by peek() in a singly-linked-list queue (Chinese localization). It fires when reading the front element of a queue whose size is zero. The guard is an explicit size()==0 check followed by @panic, because Zig has no null-return convention and silently returning a zero-value T would hide a caller bug. @panic aborts the program and cannot be caught with try/catch.

Source

Thrown at codes/zig/chapter_stack_and_queue/linkedlist_queue.zig:48

        // 析构函数（释放内存）
        pub fn deinit(self: *Self) void {
            if (self.mem_arena == null) return;
            self.mem_arena.?.deinit();
        }

        // 获取队列的长度
        pub fn size(self: *Self) usize {
            return self.que_size;
        }

        // 判断队列是否为空
        pub fn isEmpty(self: *Self) bool {
            return self.size() == 0;
        }

        // 访问队首元素
        pub fn peek(self: *Self) T {
            if (self.size() == 0) @panic("队列为空");
            return self.front.?.val;
        }  

        // 入队
        pub fn push(self: *Self, num: T) !void {
            // 在尾节点后添加 num
            var node = try self.mem_allocator.create(inc.ListNode(T));
            node.init(num);
            // 如果队列为空，则令头、尾节点都指向该节点
            if (self.front == null) {
                self.front = node;
                self.rear = node;
            // 如果队列不为空，则将该节点添加到尾节点后
            } else {
                self.rear.?.next = node;
                self.rear = node;
            }
            self.que_size += 1;

View on GitHub (pinned to 69932aed18)

Solutions

1. Guard with queue.isEmpty() before every peek() call.
2. In a consume loop, use while (!queue.isEmpty()) and call peek/pop only inside the loop body.
3. Cache queue.size() locally and branch on it before reading the front.
4. Replace peek() with a custom accessor that returns ?T if recoverable semantics are required.

Example fix

// before
var head = queue.peek(); // @panics when empty

// after
while (!queue.isEmpty()) {
    var head = queue.peek();
    _ = queue.pop();
}

// Validate non-empty before reading the front
if (!queue.isEmpty()) {
    var head = queue.peek();
}

When it happens

Trigger: Calling queue.peek() on a newly-constructed empty queue, or after pop() has drained all previously-pushed elements.

Common situations: BFS/level-order traversal reading the queue front after the last node is dequeued; porting Java/Python queue code that expects a catchable EmptyQueueException; forgetting that a single-element queue becomes empty after one pop.

Related errors

• 栈为空
• キューが空です
• キューが空です
• очередь пуста
• スタックが空です

AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13). Data as JSON: /api/errors/e4d5ad026004fb41. Report an issue: GitHub.