krahets/hello-algo · error

スタックが空です

Error message

スタックが空です

What it means

This panic is raised by peek() in a singly-linked-list stack (Japanese localization). It fires when reading the top element while stk_size == 0. The guard prevents a null stack_top dereference. @panic is uncatchable in Zig.

Source

Thrown at ja/codes/zig/chapter_stack_and_queue/linkedlist_stack.zig:46

        // デストラクタ（メモリを解放する）
        pub fn deinit(self: *Self) void {
            if (self.mem_arena == null) return;
            self.mem_arena.?.deinit();
        }

        // スタックの長さを取得
        pub fn size(self: *Self) usize {
            return self.stk_size;
        }

        // スタックが空かどうかを判定
        pub fn isEmpty(self: *Self) bool {
            return self.size() == 0;
        }

        // スタックトップの要素にアクセス
        pub fn peek(self: *Self) T {
            if (self.size() == 0) @panic("スタックが空です");
            return self.stack_top.?.val;
        }  

        // プッシュ
        pub fn push(self: *Self, num: T) !void {
            var node = try self.mem_allocator.create(inc.ListNode(T));
            node.init(num);
            node.next = self.stack_top;
            self.stack_top = node;
            self.stk_size += 1;
        } 

        // ポップ
        pub fn pop(self: *Self) T {
            var num = self.peek();
            self.stack_top = self.stack_top.?.next;
            self.stk_size -= 1;
            return num;

View on GitHub (pinned to 69932aed18)

Solutions

1. Guard with stack.isEmpty() before peek().
2. Loop with while (!stack.isEmpty()) and peek inside.
3. Verify size() > 0 before any top access.
4. Use a wrapper returning ?T if recoverable semantics are needed.

Example fix

// before
var top = stack.peek(); // @panics when empty

// after
if (stack.isEmpty()) return;
var top = stack.peek();

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

When it happens

Trigger: Calling stack.peek() before any push, or after pop() has removed the last element.

Common situations: Monotone-stack algorithms reading the top when empty; DFS stack checked at the wrong loop point; porting catchable EmptyStackException code.

Related errors

• スタックが空です
• 栈为空
• キューが空です
• 両端キューが空です
• キューが空です

AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13). Data as JSON: /api/errors/397772e7a7f7915e. Report an issue: GitHub.