krahets/hello-algo · error · IndexOutOfRangeException

インデックスが範囲外です

Error message

インデックスが範囲外です

What it means

IndexOutOfRangeException with message "インデックスが範囲外です" (Japanese for "index is out of range") is thrown by MyList.Get(int index) when index < 0 or index >= arrSize. This is the Japanese-localized equivalent of the English my_list.cs; the logic is identical.

Source

Thrown at ja/codes/csharp/chapter_array_and_linkedlist/my_list.cs:35

    public MyList() {
        arr = new int[arrCapacity];
    }

    /* リストの長さを取得（現在の要素数） */
    public int Size() {
        return arrSize;
    }

    /* リスト容量を取得する */
    public int Capacity() {
        return arrCapacity;
    }

    /* 要素にアクセス */
    public int Get(int index) {
        // インデックスが範囲外なら例外を送出する。以下同様
        if (index < 0 || index >= arrSize)
            throw new IndexOutOfRangeException("インデックスが範囲外です");
        return arr[index];
    }

    /* 要素を更新 */
    public void Set(int index, int num) {
        if (index < 0 || index >= arrSize)
            throw new IndexOutOfRangeException("インデックスが範囲外です");
        arr[index] = num;
    }

    /* 末尾に要素を追加 */
    public void Add(int num) {
        // 要素数が容量を超えると、拡張機構が発動する
        if (arrSize == arrCapacity)
            ExtendCapacity();
        arr[arrSize] = num;
        // 要素数を更新
        arrSize++;

View on GitHub (pinned to 69932aed18)

Solutions

1. Validate 0 <= index < list.Size() before calling Get().
2. Fix loop bounds to use < Size() rather than <= Size().
3. Clamp or reject out-of-range indices from external input.

Example fix

// before
MyList list = new();
list.Add(10);
int val = list.Get(1); // throws

// after
if (index >= 0 && index < list.Size())
    int val = list.Get(index);

if (index >= 0 && index < list.Size()) {
    int val = list.Get(index);
}

try {
    int val = list.Get(index);
} catch (IndexOutOfRangeException ex) when (ex.Message.Contains("範囲外")) {
    // index out of bounds — handle
}

When it happens

Trigger: Calling Get(index) where index < 0 or index >= list.Size(). On a newly constructed MyList (arrSize 0), any Get call throws.

Common situations: Off-by-one loop bounds, unvalidated external index input, or reading from a list before populating it. Japanese-speaking developers may search for the localized message string.

Related errors

• индекс выходит за границы
• Index out of bounds
• индекс выходит за границы
• 索引越界
• 索引越界

AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13). Data as JSON: /api/errors/8a960d23bd3e07ce. Report an issue: GitHub.