Skip to content
Original file line number Diff line number Diff line change
@@ -1,70 +1,65 @@
---
description: "Learn more about: Compiler Warning (level 4) C4706"
title: "Compiler Warning (level 4) C4706"
ms.date: "11/04/2016"
ms.date: "3/5/2025"
f1_keywords: ["C4706"]
helpviewer_keywords: ["C4706"]
ms.assetid: 89cd3f4f-812c-4a4b-9426-65a5a6d1b99c
---
# Compiler Warning (level 4) C4706

assignment within conditional expression
> assignment used as a condition

The test value in a conditional expression was the result of an assignment.
The test value in a conditional expression is the result of an assignment.

An assignment has a value (the value on the left side of the assignment) that can be used legally in another expression, including a test expression.

The following sample generates C4706:

```cpp
// C4706a.cpp
// compile with: /W4
int main()
{
int a = 0, b = 0;
if ( a = b ) // C4706
if (a = b) // C4706
{
}
}
```

The warning will occur even if you double the parentheses around the test condition:
Suppress the warning with `((`*expression*`))`. For example:

```cpp
// C4706b.cpp
// compile with: /W4
int main()
{
int a = 0, b = 0;
if ( ( a = b ) ) // C4706
if ((a = b)) // No warning
{
}
}
```

If your intention is to test a relation and not to make an assignment, use the `==` operator. For example, the following line tests whether a and b are equal:
If your intention is to test a relation, not to make an assignment, use the `==` operator. For example, the following tests whether a and b are equal:

```cpp
// C4706c.cpp
// compile with: /W4
int main()
{
int a = 0, b = 0;
if ( a == b )
if (a == b)
{
}
}
```

If you intend to make your test value the result of an assignment, test to ensure that the assignment is non-zero or not null. For example, the following code will not generate this warning:
If you intend to make your test value the result of an assignment, test to ensure that the assignment is non-zero or non-null. For example, the following code doesn't generate this warning:

```cpp
// C4706d.cpp
// compile with: /W4
int main()
{
int a = 0, b = 0;
if ( ( a = b ) != 0 )
if ((a = b) != 0)
{
}
}
Expand Down
10 changes: 7 additions & 3 deletions docs/sanitizers/asan-known-issues.md
Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
---
title: "AddressSanitizer known issues"
description: "Technical description of the AddressSanitizer for Microsoft C/C++ known issues."
ms.date: 1/28/2025
ms.date: 3/5/2025
helpviewer_keywords: ["AddressSanitizer known issues"]
---

Expand All @@ -23,8 +23,6 @@ These options and functionality are incompatible with [`/fsanitize=address`](../
- [C++ AMP](../parallel/amp/cpp-amp-overview.md) is unsupported, and should be disabled.
- [Universal Windows Platform](../cppcx/universal-windows-apps-cpp.md) (UWP) applications are unsupported.
- [Special case list](https://clang.llvm.org/docs/SanitizerSpecialCaseList.html) files are unsupported.
- [MFC](../mfc/mfc-concepts.md) using the optional [`alloc_dealloc_mismatch`](error-alloc-dealloc-mismatch.md) runtime option is unsupported.
- [`_CrtDumpMemoryLeaks`](../c-runtime-library/reference/crtdumpmemoryleaks.md) is unsupported, and should be disabled.

## Standard library support

Expand Down Expand Up @@ -56,6 +54,12 @@ int main() {
}
```

## Overriding operator new and delete

AddressSanitizer (ASAN) has a custom version of `operator new` and `operator delete` that it uses to find more allocation errors like [`alloc_dealloc_mismatch`](error-alloc-dealloc-mismatch.md). Running the linker with [`/INFERASANLIBS`](../build/reference/inferasanlibs.md) ensures that ASAN's `new`/`delete` override has low precedence, so that the linker chooses any `operator new` or `operator delete` overrides in other libraries over ASAN's custom versions. When this happens, ASAN may not be able to catch some errors that rely on its custom `operator new` and `operator delete`.

[MFC](../mfc/mfc-concepts.md) includes custom overrides for `operator new` and `operator delete` and so might miss errors like [`alloc_dealloc_mismatch`](error-alloc-dealloc-mismatch.md).

## Windows versions

As there are dependencies with specific Windows versions, support is focused on Windows 10. MSVC AddressSanitizer was tested on 10.0.14393 (RS1), and 10.0.21323 (prerelease insider build). [Report a bug](https://aka.ms/feedback/report?space=62) if you run into issues.
Expand Down