krahets/hello-algo · error · IndexOutOfRangeException
索引越界
Error message
索引越界
What it means
Thrown by my_list.Get(int index) (zh-hant/codes/csharp/chapter_array_and_linkedlist/my_list.cs:35) as System.IndexOutOfRangeException with message "索引越界" ("index out of range") when index is outside [0, arrSize). This is the correct, specific exception type for a bounds violation in a list-like container. Get reads 'arr[index]', so the guard protects the backing array.
Source
Thrown at zh-hant/codes/csharp/chapter_array_and_linkedlist/my_list.cs:35
public MyList() {
arr = new int[arrCapacity];
}
/* 獲取串列長度（當前元素數量）*/
public int Size() {
return arrSize;
}
/* 獲取串列容量 */
public int Capacity() {
return arrCapacity;
}
/* 訪問元素 */
public int Get(int index) {
// 索引如果越界，則丟擲異常，下同
if (index < 0 || index >= arrSize)
throw new IndexOutOfRangeException("索引越界");
return arr[index];
}
/* 更新元素 */
public void Set(int index, int num) {
if (index < 0 || index >= arrSize)
throw new IndexOutOfRangeException("索引越界");
arr[index] = num;
}
/* 在尾部新增元素 */
public void Add(int num) {
// 元素數量超出容量時，觸發擴容機制
if (arrSize == arrCapacity)
ExtendCapacity();
arr[arrSize] = num;
// 更新元素數量
arrSize++;View on GitHub (pinned to 69932aed18)
Solutions
- Validate '0 <= index < list.Size()' before calling Get.
- Fix loop bounds to '< list.Size()' rather than '<='.
- Use the list's own Size()/Capacity() rather than the backing array length when computing indices.
- Add a TryGet(int, out int) helper or clamp the index if out-of-range should not be fatal.
Example fix
// before int v = list.Get(i); // i may be == Size() // after if (i < 0 || i >= list.Size()) return; int v = list.Get(i);
Defensive patterns
Strategy: validation
Validate before calling
// Before calling Get on my_list
if (index >= 0 && index < list.Size()) {
int v = list.Get(index);
} Try / catch
try { int v = list.Get(index); }
catch (IndexOutOfRangeException) { /* index out of range: clamp or report */ } Prevention
- Validate 0 <= index < Size() before Get.
- Use '< Size()' not '<= Size()' in loop bounds.
- Do not confuse Size() with Capacity().
- Prefer the list's Size() over the backing array length for bounds.
When it happens
Trigger: Calling Get(index) where index < 0 or index >= arrSize — e.g. Get(arrSize), Get(-1), or Get on an index computed from an off-by-one loop bound.
Common situations: Looping 'for (i=0; i<=arrSize; i++)' (<= instead of <); reading the slot at the logical end (arrSize) instead of arrSize-1; passing an externally computed index without clamping; forgetting that arrCapacity != arrSize.
Related errors
AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13).
Data as JSON: /api/errors/68a1f1d665726584.
Report an issue: GitHub.