c26835.md

title	description	ms.date	f1_keywords	helpviewer_keywords
Warning C26835	Describes the Microsoft C/C++ code analysis warning C26835, its causes, and how to address it.	03/20/2023	C26835 RTL_COMPARE_MEMORY_MISUSE	C26835

Warning C26835

RtlCompareMemory returns the number of matching bytes. Consider replacing this call with RtlEqualMemory

Remarks

When RtlCompareMemory's return value is treated as a boolean, it evaluates to true when there is at least 1 equal byte before finding a difference. Moreover, comparing the result of RtlCompareMemory to 0 evaluates to false if there is at least 1 matching byte. This behavior may be unexpected because it's different from other comparison functions such as strcmp, making the code harder to understand. To check for equality, consider using RtlEqualMemory instead.

This warning is available in Visual Studio 2022 version 17.7 and later versions.

Example

int foo(const void* ptr)
{
    if (RtlCompareMemory("test", ptr, 5) == 0) // C26835
    {
        // ... 
    }
}

To fix the issue, verify if the original intention was to check for equality and replace the function call with RtlEqualMemory:

int foo(const void* ptr)
{
    if (RtlEqualMemory("test", ptr, 5)) // C26835
    {
        // ... 
    }
}

See also

RtlEqualMemory macro (wdm.h)
RtlCompareMemory function (wdm.h)