如何正确配置C++开发环境以使用memset_s函数

Got it, let's work through this memset_s undefined error you're facing with your setup: Windows SDK 10.0, v142 toolset, and C++14 standard. You've already followed the guidance around the __STDC_WANT_LIB_EXT1__ macro and conditional check, so let's cover the extra steps specific to MSVC:

1. Ensure your macro definition is the absolute first line #

The #define __STDC_WANT_LIB_EXT1__ 1 line must come before any #include statements—even before custom headers that might indirectly pull in system headers like <string.h>. If you define it after any include, the compiler will load the non-extended version of the standard library headers first, and memset_s won't be exposed. For example:

// Correct order
#define __STDC_WANT_LIB_EXT1__ 1
#include <string.h>
#include <iostream> // Other headers come later

2. Enable conformance mode in project settings #

MSVC's default C++ mode doesn't fully enable C11's bounds-checking functions like memset_s out of the box. To fix this:

• Right-click your project → Properties
• Navigate to Configuration Properties > C/C++ > Language
• Set "Conformance mode" to Yes (/permissive-)
• Also, set "C Language Standard" to C17 or higher (this affects how the C standard library is loaded, even in C++ projects)

3. Verify header includes (try for C++) #

While <string.h> should work, in C++ projects, replacing it with <cstring> can sometimes resolve header-related inconsistencies. Keep the macro definition first:

#define __STDC_WANT_LIB_EXT1__ 1
#include <cstring>

Also, double-check your project's preprocessor definitions to make sure there's no macro like _CRT_DISABLE_PERFCRIT_LOCKS accidentally disabling security functions (note: _CRT_SECURE_NO_WARNINGS only suppresses warnings, not function definitions).

4. Fall back to MSVC's native memset_s (if needed) #

If the C11 standard version still won't link, you can use MSVC's own extension version of memset_s—it has the exact same signature as the C11 standard, so your code won't need changes. You don't need the __STDC_WANT_LIB_EXT1__ macro for this; just call it directly, since MSVC enables secure CRT functions by default:

memset_s(dest, sizeof(dest), 0, count);

内容的提问来源于stack exchange，提问作者user2896152