我应该如何在 C++ 中正确使用 FormatMessage()？

发布于 2024-07-12 05:26:24 字数 462 浏览 10 评论 0原文

没有：

如何使用 FormatMessage () 获取 HRESULT 的错误文本？

 HRESULT hresult = application.CreateInstance("Excel.Application");

 if (FAILED(hresult))
 {
     // what should i put here to obtain a human-readable
     // description of the error?
     exit (hresult);
 }

原文

Without:

How can I use FormatMessage() to get the error text for a HRESULT?

 HRESULT hresult = application.CreateInstance("Excel.Application");

 if (FAILED(hresult))
 {
     // what should i put here to obtain a human-readable
     // description of the error?
     exit (hresult);
 }

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末骤雨初歇 2024-07-19 05:26:25

以下是从系统返回 HRESULT 错误消息（在本例中名为 hresult，或者您可以将其替换为 GetLastError()）的正确方法

LPTSTR errorText = NULL;

FormatMessage(
   // use system message tables to retrieve error text
   FORMAT_MESSAGE_FROM_SYSTEM
   // allocate buffer on local heap for error text
   |FORMAT_MESSAGE_ALLOCATE_BUFFER
   // Important! will fail otherwise, since we're not 
   // (and CANNOT) pass insertion parameters
   |FORMAT_MESSAGE_IGNORE_INSERTS,  
   NULL,    // unused with FORMAT_MESSAGE_FROM_SYSTEM
   hresult,
   MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
   (LPTSTR)&errorText,  // output 
   0, // minimum size for output buffer
   NULL);   // arguments - see note 
   
if ( NULL != errorText )
{
   // ... do something with the string `errorText` - log it, display it to the user, etc.

   // release memory allocated by FormatMessage()
   LocalFree(errorText);
   errorText = NULL;
}

：这与 David Hanak 的答案之间的区别在于使用 FORMAT_MESSAGE_IGNORE_INSERTS 标志。 MSDN 对于如何使用插入有点不清楚，但是 Raymond Chen 指出，您在检索系统消息时永远不应该使用它们，因为您无法知道系统需要哪些插入。

FWIW，如果您使用的是 Visual C++，您可以使用 _com_error 类：

{
   _com_error error(hresult);
   LPCTSTR errorText = error.ErrorMessage();
   
   // do something with the error...

   //automatic cleanup when error goes out of scope
}

据我所知，不直接属于 MFC 或 ATL。

Here's the proper way to get an error message back from the system for an HRESULT (named hresult in this case, or you can replace it with GetLastError()):

LPTSTR errorText = NULL;

FormatMessage(
   // use system message tables to retrieve error text
   FORMAT_MESSAGE_FROM_SYSTEM
   // allocate buffer on local heap for error text
   |FORMAT_MESSAGE_ALLOCATE_BUFFER
   // Important! will fail otherwise, since we're not 
   // (and CANNOT) pass insertion parameters
   |FORMAT_MESSAGE_IGNORE_INSERTS,  
   NULL,    // unused with FORMAT_MESSAGE_FROM_SYSTEM
   hresult,
   MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
   (LPTSTR)&errorText,  // output 
   0, // minimum size for output buffer
   NULL);   // arguments - see note 
   
if ( NULL != errorText )
{
   // ... do something with the string `errorText` - log it, display it to the user, etc.

   // release memory allocated by FormatMessage()
   LocalFree(errorText);
   errorText = NULL;
}

The key difference between this and David Hanak's answer is the use of the FORMAT_MESSAGE_IGNORE_INSERTS flag. MSDN is a bit unclear on how insertions should be used, but Raymond Chen notes that you should never use them when retrieving a system message, as you've no way of knowing which insertions the system expects.

FWIW, if you're using Visual C++ you can make your life a bit easier by using the _com_error class:

{
   _com_error error(hresult);
   LPCTSTR errorText = error.ErrorMessage();
   
   // do something with the error...

   //automatic cleanup when error goes out of scope
}

Not part of MFC or ATL directly as far as I'm aware.

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故乡的云 2024-07-19 05:26:25

请记住，您不能执行以下操作：

{
   LPCTSTR errorText = _com_error(hresult).ErrorMessage();

   // do something with the error...

   //automatic cleanup when error goes out of scope
}

在堆栈上创建和销毁类时，使 errorText 指向无效位置。在大多数情况下，该位置仍将包含错误字符串，但在编写线程应用程序时，这种可能性很快就会消失。

因此，总是按照上面 Shog9 的回答进行操作：

{
   _com_error error(hresult);
   LPCTSTR errorText = error.ErrorMessage();

   // do something with the error...

   //automatic cleanup when error goes out of scope
}

Keep in mind that you cannot do the following:

{
   LPCTSTR errorText = _com_error(hresult).ErrorMessage();

   // do something with the error...

   //automatic cleanup when error goes out of scope
}

As the class is created and destroyed on the stack leaving errorText to point to an invalid location. In most cases this location will still contain the error string, but that likelihood falls away fast when writing threaded applications.

So always do it as follows as answered by Shog9 above:

{
   _com_error error(hresult);
   LPCTSTR errorText = error.ErrorMessage();

   // do something with the error...

   //automatic cleanup when error goes out of scope
}

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久伴你 2024-07-19 05:26:25

尝试这个：

void PrintLastError (const char *msg /* = "Error occurred" */) {
        DWORD errCode = GetLastError();
        char *err;
        if (!FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                           NULL,
                           errCode,
                           MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // default language
                           (LPTSTR) &err,
                           0,
                           NULL))
            return;

        static char buffer[1024];
        _snprintf(buffer, sizeof(buffer), "ERROR: %s: %s\n", msg, err);
        OutputDebugString(buffer); // or otherwise log it
        LocalFree(err);
}

Try this:

void PrintLastError (const char *msg /* = "Error occurred" */) {
        DWORD errCode = GetLastError();
        char *err;
        if (!FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                           NULL,
                           errCode,
                           MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // default language
                           (LPTSTR) &err,
                           0,
                           NULL))
            return;

        static char buffer[1024];
        _snprintf(buffer, sizeof(buffer), "ERROR: %s: %s\n", msg, err);
        OutputDebugString(buffer); // or otherwise log it
        LocalFree(err);
}

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沉睡月亮 2024-07-19 05:26:25

从 c++11 开始，您可以使用标准库代替 FormatMessage：

#include <system_error>

std::string message = std::system_category().message(hr)

Since c++11, you can use the standard library instead of FormatMessage:

#include <system_error>

std::string message = std::system_category().message(hr)

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你好，陌生人 2024-07-19 05:26:25

这更多的是对大多数答案的补充，但不使用 LocalFree(errorText)，而是使用 HeapFree 函数：

::HeapFree(::GetProcessHeap(), NULL, errorText);

来自 MSDN 站点：

Windows 10：
LocalFree 不在现代 SDK 中，因此不能用于释放结果缓冲区。相反，请使用 HeapFree（GetProcessHeap()、altedMessage）。在这种情况下，这与在内存上调用 LocalFree 相同。

更新
我发现 LocalFree 的 SDK 版本为 10.0.10240.0（WinBase.h 中的第 1108 行）。但是，上面的链接中仍然存在警告。

#pragma region Desktop Family or OneCore Family
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP | WINAPI_PARTITION_SYSTEM)

WINBASEAPI
_Success_(return==0)
_Ret_maybenull_
HLOCAL
WINAPI
LocalFree(
    _Frees_ptr_opt_ HLOCAL hMem
    );

#endif /* WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP | WINAPI_PARTITION_SYSTEM) */
#pragma endregion

更新2
我还建议使用 FORMAT_MESSAGE_MAX_WIDTH_MASK 标志来整理系统消息中的换行符。

来自 MSDN 站点：

FORMAT_MESSAGE_MAX_WIDTH_MASK
该函数忽略消息定义文本中的常规换行符。该函数将消息定义文本中的硬编码换行符存储到输出缓冲区中。该函数不会生成新的换行符。

更新3
似乎有 2 个特定的系统错误代码不会使用推荐的方法返回完整消息：

为什么 FormatMessage 只为 ERROR_SYSTEM_PROCESS_TERMINATED 和 ERROR_UNHANDLED_EXCEPTION 系统错误创建部分消息？

This is more an addition to the majority of the answers, but instead of using LocalFree(errorText) use the HeapFree function:

::HeapFree(::GetProcessHeap(), NULL, errorText);

From the MSDN site:

Windows 10:
LocalFree is not in the modern SDK, so it cannot be used to free the result buffer. Instead, use HeapFree (GetProcessHeap(), allocatedMessage). In this case, this is the same as calling LocalFree on memory.

Update
I found that LocalFree is in version 10.0.10240.0 of the SDK (line 1108 in WinBase.h). However, the warning still exists in the link above.

#pragma region Desktop Family or OneCore Family
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP | WINAPI_PARTITION_SYSTEM)

WINBASEAPI
_Success_(return==0)
_Ret_maybenull_
HLOCAL
WINAPI
LocalFree(
    _Frees_ptr_opt_ HLOCAL hMem
    );

#endif /* WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP | WINAPI_PARTITION_SYSTEM) */
#pragma endregion

Update 2
I would also suggest using the FORMAT_MESSAGE_MAX_WIDTH_MASK flag to tidy up line breaks in system messages.

From the MSDN site:

FORMAT_MESSAGE_MAX_WIDTH_MASK
The function ignores regular line breaks in the message definition text. The function stores hard-coded line breaks in the message definition text into the output buffer. The function generates no new line breaks.

Update 3
There appears to be 2 particular system error codes that do not return the full message using the recommended approach:

Why does FormatMessage only create partial messages for ERROR_SYSTEM_PROCESS_TERMINATED and ERROR_UNHANDLED_EXCEPTION system errors?

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对不⑦ 2024-07-19 05:26:25

这是处理 Unicode 的 David 函数的一个版本

void HandleLastError(const TCHAR *msg /* = "Error occured" */) {
    DWORD errCode = GetLastError();
    TCHAR *err;
    if (!FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                       NULL,
                       errCode,
                       MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // default language
                       (LPTSTR) &err,
                       0,
                       NULL))
        return;

    //TRACE("ERROR: %s: %s", msg, err);
    TCHAR buffer[1024];
    _sntprintf_s(buffer, sizeof(buffer) / sizeof(buffer[0]), _T("ERROR: %s: %s\n"), msg, err);
    OutputDebugString(buffer);
    LocalFree(err);
}

Here is a version of David's function that handles Unicode

void HandleLastError(const TCHAR *msg /* = "Error occured" */) {
    DWORD errCode = GetLastError();
    TCHAR *err;
    if (!FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                       NULL,
                       errCode,
                       MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // default language
                       (LPTSTR) &err,
                       0,
                       NULL))
        return;

    //TRACE("ERROR: %s: %s", msg, err);
    TCHAR buffer[1024];
    _sntprintf_s(buffer, sizeof(buffer) / sizeof(buffer[0]), _T("ERROR: %s: %s\n"), msg, err);
    OutputDebugString(buffer);
    LocalFree(err);
}

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天生の放荡 2024-07-19 05:26:25

正如其他答案中所指出的：

FormatMessage 采用 DWORD 结果而不是 HRESULT （通常是 GetLastError()）。
需要 LocalFree 来释放由 FormatMessage 分配的内存

我采纳了上述几点，并为我的答案添加了更多内容：

将 FormatMessage 包装在根据需要分配和释放内存的类
使用运算符重载（例如operator LPTSTR() const { return ...; } 以便您的类可以用作字符串

class CFormatMessage
{
public:
    CFormatMessage(DWORD dwMessageId,
                   DWORD dwLanguageId = MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT)) :
        m_text(NULL)
    {
        Assign(dwMessageId, dwLanguageId);
    }

    ~CFormatMessage()
    {
        Clear();
    }

    void Clear()
    {
        if (m_text)
        {
            LocalFree(m_text);
            m_text = NULL;
        }
    }

    void Assign(DWORD dwMessageId,
                DWORD dwLanguageId = MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT))
    {
        Clear();
        DWORD dwFlags = FORMAT_MESSAGE_FROM_SYSTEM
            | FORMAT_MESSAGE_ALLOCATE_BUFFER
            | FORMAT_MESSAGE_IGNORE_INSERTS,
        FormatMessage(
            dwFlags,
            NULL,
            dwMessageId,
            dwLanguageId,
            (LPTSTR) &m_text,
            0,
            NULL);
    }

    LPTSTR text() const { return m_text; }
    operator LPTSTR() const { return text(); }

protected:
    LPTSTR m_text;

};

查找更完整的版本上面的代码在这里： https://github.com/stephenquan/FormatMessage

使用上面的类，用法很简单：

    std::wcout << (LPTSTR) CFormatMessage(GetLastError()) << L"\n";

As pointed out in other answers:

FormatMessage takes a DWORD result not a HRESULT (typically GetLastError()).
LocalFree is needed to release memory that was allocated by FormatMessage

I took the above points and added a few more for my answer:

Wrap the FormatMessage in a class to allocate and release memory as needed
Use operator overload (e.g. operator LPTSTR() const { return ...; } so that your class can be used as a string

class CFormatMessage
{
public:
    CFormatMessage(DWORD dwMessageId,
                   DWORD dwLanguageId = MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT)) :
        m_text(NULL)
    {
        Assign(dwMessageId, dwLanguageId);
    }

    ~CFormatMessage()
    {
        Clear();
    }

    void Clear()
    {
        if (m_text)
        {
            LocalFree(m_text);
            m_text = NULL;
        }
    }

    void Assign(DWORD dwMessageId,
                DWORD dwLanguageId = MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT))
    {
        Clear();
        DWORD dwFlags = FORMAT_MESSAGE_FROM_SYSTEM
            | FORMAT_MESSAGE_ALLOCATE_BUFFER
            | FORMAT_MESSAGE_IGNORE_INSERTS,
        FormatMessage(
            dwFlags,
            NULL,
            dwMessageId,
            dwLanguageId,
            (LPTSTR) &m_text,
            0,
            NULL);
    }

    LPTSTR text() const { return m_text; }
    operator LPTSTR() const { return text(); }

protected:
    LPTSTR m_text;

};

Find a more complete version of the above code here: https://github.com/stephenquan/FormatMessage

With the above class, the usage is simply:

    std::wcout << (LPTSTR) CFormatMessage(GetLastError()) << L"\n";

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み格子的夏天 2024-07-19 05:26:25

下面的代码是我编写的 C++ 等效代码，与 Microsoft 的 ErrorExit() 但稍作修改以避免所有宏并使用 unicode。这里的想法是避免不必要的强制转换和 malloc。我无法逃脱所有的 C 演员阵容，但这是我能召集的最好的演员阵容。与 FormatMessageW() 相关，它需要由格式函数分配一个指针以及来自 GetLastError() 的错误 ID。 static_cast之后的指针可以像普通的wchar_t指针一样使用。

#include <string>
#include <windows.h>

void __declspec(noreturn) error_exit(const std::wstring FunctionName)
{
    // Retrieve the system error message for the last-error code
    const DWORD ERROR_ID = GetLastError();
    void* MsgBuffer = nullptr;
    LCID lcid;
    GetLocaleInfoEx(L"en-US", LOCALE_RETURN_NUMBER | LOCALE_ILANGUAGE, (wchar_t*)&lcid, sizeof(lcid));

    //get error message and attach it to Msgbuffer
    FormatMessageW(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL, ERROR_ID, lcid, (wchar_t*)&MsgBuffer, 0, NULL);
    //concatonate string to DisplayBuffer
    const std::wstring DisplayBuffer = FunctionName + L" failed with error " + std::to_wstring(ERROR_ID) + L": " + static_cast<wchar_t*>(MsgBuffer);

    // Display the error message and exit the process
    MessageBoxExW(NULL, DisplayBuffer.c_str(), L"Error", MB_ICONERROR | MB_OK, static_cast<WORD>(lcid));

    ExitProcess(ERROR_ID);
}

The code below is code is the C++ equivalent I've written out in contrast to Microsoft's ErrorExit() but slightly altered to avoid all macros and use unicode. The idea here is to avoid unnecessary casts and mallocs. I couldn't escape all of the C casts but this is the best I could muster. Pertaining to FormatMessageW(), which requires a pointer to be allocated by the format function and the Error Id from the GetLastError(). The pointer after static_cast can be used like a normal wchar_t pointer.

#include <string>
#include <windows.h>

void __declspec(noreturn) error_exit(const std::wstring FunctionName)
{
    // Retrieve the system error message for the last-error code
    const DWORD ERROR_ID = GetLastError();
    void* MsgBuffer = nullptr;
    LCID lcid;
    GetLocaleInfoEx(L"en-US", LOCALE_RETURN_NUMBER | LOCALE_ILANGUAGE, (wchar_t*)&lcid, sizeof(lcid));

    //get error message and attach it to Msgbuffer
    FormatMessageW(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL, ERROR_ID, lcid, (wchar_t*)&MsgBuffer, 0, NULL);
    //concatonate string to DisplayBuffer
    const std::wstring DisplayBuffer = FunctionName + L" failed with error " + std::to_wstring(ERROR_ID) + L": " + static_cast<wchar_t*>(MsgBuffer);

    // Display the error message and exit the process
    MessageBoxExW(NULL, DisplayBuffer.c_str(), L"Error", MB_ICONERROR | MB_OK, static_cast<WORD>(lcid));

    ExitProcess(ERROR_ID);
}

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~没有更多了~