Learn Editor: Update c26839.md

Author: Rastaban

docs/code-quality/c26839.md

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-Warning C26839
+# Warning C26839
+
+
+> Array new allocation size is the result of a signed to unsigned narrowing conversion that could result in overflow if the signed value is negative
+
+## Remarks
+
+This warning reports that the size specified for a array new allocation may be the result of the conversion of a possibly negative signed value to an unsigned value. For example:
+
+```cpp
+int* CreateIntArray(int size)
+{
+    int* intArray = new int[size];
+    return intArray;
+}
+```
+
+In the expression `new int[size]`, `size` is signed. The compiler will convert the signed value to an unsigned value when calculating how many bytes need to be allocated for the array.
+When `size` is negative, the result of that calculation may overflow or have unexpected results.
+
+This check is the same as [`C26838`](c26838.md), but applies only to array new `new T[]`.
+
+This check sometimes fails to recognize that certain checks can prevent overflows because the check is conservative.
+
+This warning is available in Visual Studio 2022 version 17.12 and later versions.
+
+## Example
+
+To fix the previous code example in which the size calculation might overflow due to a negative signed value, introduce a check to make sure it won't. For example:
+
+```cpp
+int* CreateIntArray(int size)
+{
+    if (size < 0)
+        return nullptr;
+
+    int* intArray = new int[size];
+    return intArray;
+}
+```
+
+## See also
+
+[`C26831`](c26831.md)\
+[`C26832`](c26832.md)\
+[`C26838`](c26833.md)\
+[`C26838`](c26838.md)