SetEnvironmentVariable() 似乎没有设置可以通过 getenv() 检索的值 [英] SetEnvironmentVariable() does not seem to set values that can be retrieved by getenv()

问题描述

我有一个 EXE，它在启动时通过 Windows API SetEnvironmentVariable()环境变量(即:MAGICK_CODER_MODULE_PATH=xxx)>.

I have an EXE which, at startup, sets an environment variable (ie: MAGICK_CODER_MODULE_PATH=xxx) via the Windows API SetEnvironmentVariable().

当我在进程资源管理器(来自 SysInternals)中查看设置为我的 EXE 的环境变量列表时，我可以看到我之前设置的环境变量(MAGICK_CODER_MODULE_PATH)，所以一切看起来都很好点.

When I look in Process Explorer (from SysInternals) at the list of environment variables set to my EXE I can see the environment variable I just set before (MAGICK_CODER_MODULE_PATH), so everything looks good at this point.

然后我指示我的 EXE 通过 LoadLibrary() 加载一个 DLL.稍后，当此 DLL 尝试通过 getenv("MAGICK_CODER_MODULE_PATH") 获取我的环境变量的值时，问题出现了:它返回 NULL！这怎么可能?看起来 getenv() 忽略了我之前用 SetEnvironmentVariable() 设置的值.

Then I instruct my EXE to load a DLL via LoadLibrary(). The problem arises a little later when this DLL tries to get the value of my environment variable via getenv("MAGICK_CODER_MODULE_PATH"): it returns NULL! How could this be possible? It looks like getenv() ignores the value I just set before with SetEnvironmentVariable().

注意:

• 使用旧版本的 Visual Studio 编译 DLL 时似乎不会发生这种情况(可能与 vcruntime140.dll/msvcp140.dll 相关).
• 如果我打开命令提示符，请执行 @SET MAGICK_CODER_MODULE_PATH=xxx，然后从该命令提示符启动我的 EXE，然后一切正常:DLL 成功获取了 MAGICK_CODER_MODULE_PATH 的值 通过 getenv().

• This seems to not happen when the DLL is compiled with an old version of Visual Studio (maybe related to vcruntime140.dll / msvcp140.dll).
• If I open a command prompt, do @SET MAGICK_CODER_MODULE_PATH=xxx, and from this command prompt then launch my EXE, then everything works fine: the DLL successfully gets the value of MAGICK_CODER_MODULE_PATH via getenv().

推荐答案

您正在混合 API:Windows 的 SetEnvironmentVariable 绕过 C++ 运行时，因此存储在您的环境中的副本程序未更新.后面的 getenv 调用会查看此副本，但未找到您的更改.

You're mixing APIs: Windows' SetEnvironmentVariable bypasses the C++ runtime, so that the copy of the environment that is stored in your program is not updated. The later getenv call looks into this copy and doesn't find your change.

对两个调用使用相同的 API 级别.getenv 和 _putenv，或使用 Windows API GetEnvironmentVariable 和 SetEnvironmentVariable.

Use the same API level for both calls. Either getenv and _putenv, or use the Windows API GetEnvironmentVariable and SetEnvironmentVariable.

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