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docs/api/memory/linear-allocator/get-used-size.md

@@ -0,0 +1,39 @@
+# LinearAllocator::GetUsedSize
+
+```cpp
+size_t GetUsedSize() const;
+```
+
+返回当前已使用的字节数，即内部偏移量的值。此值在 `Allocate` 后增加，在 `Clear` 或 `SetMarker` 后可能减少（取决于设置的目标位置）。
+
+**参数：** 无
+
+**返回：** 已使用的字节数
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+#include <XCEngine/Memory/LinearAllocator.h>
+
+LinearAllocator allocator(1024);
+
+size_t before = allocator.GetUsedSize(); // 0
+
+allocator.Allocate(128);
+allocator.Allocate(256);
+
+size_t after = allocator.GetUsedSize(); // 384
+
+void* marker = allocator.GetMarker();
+allocator.Allocate(64);
+size_t with_temp = allocator.GetUsedSize(); // 448
+
+allocator.SetMarker(marker);
+size_t after_rollback = allocator.GetUsedSize(); // 384
+```
+
+## 相关文档
+
+- [LinearAllocator 总览](linear-allocator.md) - 返回类总览