如何从GetLastError()返回的错误代码中获取错误消息?

After a Windows API call, how can I get the last error message in a textual form?

在Windows API调用之后，如何以文本形式获取最后一条错误消息?

GetLastError() returns an integer value, not a text message.

GetLastError()返回一个整数值，而不是一条文本消息。

Thanks.

谢谢。

10 个解决方案

#1

//Returns the last Win32 error, in string format. Returns an empty string if there is no error.
std::string GetLastErrorAsString()
{
    //Get the error message, if any.
    DWORD errorMessageID = ::GetLastError();
    if(errorMessageID == 0)
        return std::string(); //No error message has been recorded

    LPSTR messageBuffer = nullptr;
    size_t size = FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
                                 NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&messageBuffer, 0, NULL);

    std::string message(messageBuffer, size);

    //Free the buffer.
    LocalFree(messageBuffer);

    return message;
}

#2

Updated (11/2017) to take into consideration some comments.

修订(2017年11月)以考虑一些评论。

Easy example:

简单的例子:

wchar_t buf[256];
FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
               NULL, GetLastError(), MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), 
               buf, (sizeof(buf) / sizeof(wchar_t)), NULL);

#3

MSDN has some sample code that demonstrates how to use FormatMessage() and GetLastError() together: Retrieving the Last-Error Code

MSDN有一些示例代码，演示了如何将FormatMessage()和GetLastError()结合使用:检索Last-Error代码

#4

FormatMessage will turn GetLastError's integer return into a text message.

FormatMessage将把GetLastError的整数返回到文本消息中。

#5

In general, you need to use FormatMessage to convert from a Win32 error code to text.

通常，您需要使用FormatMessage从Win32错误代码转换为文本。

From the MSDN documentation:

从MSDN文档:

Formats a message string. The function requires a message definition as input. The message definition can come from a buffer passed into the function. It can come from a message table resource in an already-loaded module. Or the caller can ask the function to search the system's message table resource(s) for the message definition. The function finds the message definition in a message table resource based on a message identifier and a language identifier. The function copies the formatted message text to an output buffer, processing any embedded insert sequences if requested.

消息格式字符串。函数需要消息定义作为输入。消息定义可以来自传入函数的缓冲区。它可以来自已加载模块中的消息表资源。或者，调用者可以要求函数搜索系统的消息表资源以获取消息定义。函数根据消息标识符和语言标识符在消息表资源中查找消息定义。该函数将格式化的消息文本复制到输出缓冲区，如果需要，将处理任何嵌入的插入序列。

The declaration of FormatMessage:

FormatMessage宣言:

DWORD WINAPI FormatMessage(
  __in      DWORD dwFlags,
  __in_opt  LPCVOID lpSource,
  __in      DWORD dwMessageId, // your error code
  __in      DWORD dwLanguageId,
  __out     LPTSTR lpBuffer,
  __in      DWORD nSize,
  __in_opt  va_list *Arguments
);

#6

If you're using c# you can use this code:

如果您使用c#，您可以使用以下代码:

using System.Runtime.InteropServices;

public static class WinErrors
{
    #region definitions
    [DllImport("kernel32.dll", SetLastError = true)]
    static extern IntPtr LocalFree(IntPtr hMem);

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern int FormatMessage(FormatMessageFlags dwFlags, IntPtr lpSource, uint dwMessageId, uint dwLanguageId, ref IntPtr lpBuffer, uint nSize, IntPtr Arguments);

    [Flags]
    private enum FormatMessageFlags : uint
    {
        FORMAT_MESSAGE_ALLOCATE_BUFFER = 0x00000100,
        FORMAT_MESSAGE_IGNORE_INSERTS = 0x00000200,
        FORMAT_MESSAGE_FROM_SYSTEM = 0x00001000,
        FORMAT_MESSAGE_ARGUMENT_ARRAY = 0x00002000,
        FORMAT_MESSAGE_FROM_HMODULE = 0x00000800,
        FORMAT_MESSAGE_FROM_STRING = 0x00000400,
    }
    #endregion

    /// <summary>
    /// Gets a user friendly string message for a system error code
    /// </summary>
    /// <param name="errorCode">System error code</param>
    /// <returns>Error string</returns>
    public static string GetSystemMessage(int errorCode)
    {
        try
        {
            IntPtr lpMsgBuf = IntPtr.Zero;

            int dwChars = FormatMessage(
                FormatMessageFlags.FORMAT_MESSAGE_ALLOCATE_BUFFER | FormatMessageFlags.FORMAT_MESSAGE_FROM_SYSTEM | FormatMessageFlags.FORMAT_MESSAGE_IGNORE_INSERTS,
                IntPtr.Zero,
                (uint) errorCode,
                0, // Default language
                ref lpMsgBuf,
                0,
                IntPtr.Zero);
            if (dwChars == 0)
            {
                // Handle the error.
                int le = Marshal.GetLastWin32Error();
                return "Unable to get error code string from System - Error " + le.ToString();
            }

            string sRet = Marshal.PtrToStringAnsi(lpMsgBuf);

            // Free the buffer.
            lpMsgBuf = LocalFree(lpMsgBuf);
            return sRet;
        }
        catch (Exception e)
        {
            return "Unable to get error code string from System -> " + e.ToString();
        }
    }
}

#7

GetLastError returns a numerical error code. To obtain a descriptive error message (e.g., to display to a user), you can call FormatMessage:

GetLastError返回一个数值错误代码。要获取描述性错误消息(例如，显示给用户)，可以调用FormatMessage:

// This functions fills a caller-defined character buffer (pBuffer)
// of max length (cchBufferLength) with the human-readable error message
// for a Win32 error code (dwErrorCode).
// 
// Returns TRUE if successful, or FALSE otherwise.
// If successful, pBuffer is guaranteed to be NUL-terminated.
// On failure, the contents of pBuffer are undefined.
BOOL GetErrorMessage(DWORD dwErrorCode, LPTSTR pBuffer, DWORD cchBufferLength)
{
    if (cchBufferLength == 0)
    {
        return FALSE;
    }

    DWORD cchMsg = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
                                 NULL,  /* (not used with FORMAT_MESSAGE_FROM_SYSTEM) */
                                 dwErrorCode,
                                 MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                                 pBuffer,
                                 cchBufferLength,
                                 NULL);
    return (cchMsg > 0);
}

In C++, you can simplify the interface considerably by using the std::string class:

在c++中，可以使用std::string类:

#include <Windows.h>
#include <system_error>
#include <memory>
#include <string>
typedef std::basic_string<TCHAR> String;

String GetErrorMessage(DWORD dwErrorCode)
{
    LPTSTR psz{ nullptr };
    const DWORD cchMsg = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM
                                         | FORMAT_MESSAGE_IGNORE_INSERTS
                                         | FORMAT_MESSAGE_ALLOCATE_BUFFER,
                                       NULL, // (not used with FORMAT_MESSAGE_FROM_SYSTEM)
                                       dwErrorCode,
                                       MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                                       reinterpret_cast<LPTSTR>(&psz),
                                       0,
                                       NULL);
    if (cchMsg > 0)
    {
        // Assign buffer to smart pointer with custom deleter so that memory gets released
        // in case String's c'tor throws an exception.
        auto deleter = [](void* p) { ::HeapFree(::GetProcessHeap(), 0, p); };
        std::unique_ptr<TCHAR, decltype(deleter)> ptrBuffer(psz, deleter);
        return String(ptrBuffer.get(), cchMsg);
    }
    else
    {
        auto error_code{ ::GetLastError() };
        throw std::system_error( error_code, std::system_category(),
                                 "Failed to retrieve error message string.");
    }
}

NOTE: These functions also work for HRESULT values. Just change the first parameter from DWORD dwErrorCode to HRESULT hResult. The rest of the code can remain unchanged.

注意:这些函数也适用于HRESULT值。只需将第一个参数从DWORD dwErrorCode更改为HRESULT HRESULT。其余的代码可以保持不变。

---

These implementations provide the following improvements over the existing answers:

• Complete sample code, not just a reference to the API to call.
• 完整的示例代码，而不仅仅是要调用的API的引用。
• Provides both C and C++ implementations.
• 提供C和c++实现。
• Works for both Unicode and MBCS project settings.
• 适用于Unicode和MBCS项目设置。
• Takes the error code as an input parameter. This is important, as a thread's last error code is only valid at well defined points. An input parameter allows the caller to follow the documented contract.
• 将错误代码作为输入参数。这很重要，因为线程的最后一个错误代码只在定义良好的点上有效。输入参数允许调用者遵循文档化的契约。
• Implements proper exception safety. Unlike all of the other solutions that implicitly use exceptions, this implementation will not leak memory in case an exception is thrown while constructing the return value.
• 实现适当的异常安全的。与所有隐式使用异常的其他解决方案不同，此实现在构造返回值时抛出异常时不会泄漏内存。
• Proper use of the FORMAT_MESSAGE_IGNORE_INSERTS flag. See The importance of the FORMAT_MESSAGE_IGNORE_INSERTS flag for more information.
• 正确使用format_message_ignore_insert标志。有关更多信息，请参见format_message_ignore_insert标志的重要性。
• Proper error handling/error reporting, unlike some of the other answers, that silently ignore errors.
• 正确的错误处理/错误报告，与其他一些答案不同，它会默默地忽略错误。

---

This answer has been incorporated from Stack Overflow Documentation. The following users have contributed to the example: stackptr, Ajay, Cody Gray♦, IInspectable.

#8

If you need to support MBCS as well as Unicode, Mr.C64's answer is not quite enough. The buffer must be declared TCHAR, and cast to LPTSTR. Note that this code doesn't deal with the annoying newline that Microsoft appends to the error message.

如果您需要支持MBCS和Unicode，那么c64先生的答案是不够的。缓冲区必须声明为TCHAR，并强制转换为LPTSTR。注意，这段代码没有处理Microsoft附加到错误消息的恼人的换行。

CString FormatErrorMessage(DWORD ErrorCode)
{
    TCHAR   *pMsgBuf = NULL;
    DWORD   nMsgLen = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL, ErrorCode, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        reinterpret_cast<LPTSTR>(&pMsgBuf), 0, NULL);
    if (!nMsgLen)
        return _T("FormatMessage fail");
    CString sMsg(pMsgBuf, nMsgLen);
    LocalFree(pMsgBuf);
    return sMsg;
}

Also, for brevity I find the following method useful:

此外，为了简洁，我发现下面的方法很有用:

CString GetLastErrorString()
{
    return FormatErrorMessage(GetLastError());
}

#9

void WinErrorCodeToString(DWORD ErrorCode, string& Message)
{
char* locbuffer = NULL;
DWORD count = FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER, NULL, ErrorCode,
    0, (LPSTR)&locbuffer, 0, nullptr);
if (locbuffer)
{
    if (count)
    {
        int c;
        int back = 0;
        //
        // strip any trailing "\r\n"s and replace by a single "\n"
        //
        while (((c = *CharPrevA(locbuffer, locbuffer + count)) == '\r') ||
            (c == '\n')) {
            count--;
            back++;
        }

        if (back) {
            locbuffer[count++] = '\n';
            locbuffer[count] = '\0';
        }

        Message = "Error: ";
        Message += locbuffer;
    }
    LocalFree(locbuffer);
}
else
{
    Message = "Unknown error code: " + to_string(ErrorCode);
}
}

#10

i'll leave this here since i will need to use it later. It's a source for a small binary compatible tool that will work equally well in assembly, C and C++.

我把它留在这里，因为我以后需要用到它。它是一个小型二进制兼容工具的源代码，在汇编语言C和c++中同样适用。

GetErrorMessageLib.c (compiled to GetErrorMessageLib.dll)

GetErrorMessageLib。GetErrorMessageLib.dll c(编译)

#include <Windows.h>

/***
 * returns 0 if there was enough space, size of buffer in bytes needed
 * to fit the result, if there wasn't enough space. -1 on error.
 */
__declspec(dllexport)
int GetErrorMessageA(DWORD dwErrorCode, LPSTR lpResult, DWORD dwBytes)
{    
    LPSTR tmp;
    DWORD result_len;

    result_len = FormatMessageA (
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_ALLOCATE_BUFFER,
        NULL,
        dwErrorCode,
        LANG_SYSTEM_DEFAULT,
        (LPSTR)&tmp,
        0,
        NULL
    );        

    if (result_len == 0) {
        return -1;
    }

    // FormatMessage's return is 1 character too short.
    ++result_len;

    strncpy(lpResult, tmp, dwBytes);

    lpResult[dwBytes - 1] = 0;
    LocalFree((HLOCAL)tmp);

    if (result_len <= dwBytes) {
        return 0;
    } else {
        return result_len;
    }
}

/***
 * returns 0 if there was enough space, size of buffer in bytes needed
 * to fit the result, if there wasn't enough space. -1 on error.
 */
__declspec(dllexport)
int GetErrorMessageW(DWORD dwErrorCode, LPWSTR lpResult, DWORD dwBytes)
{   
    LPWSTR tmp;
    DWORD nchars;
    DWORD result_bytes;

    nchars = dwBytes >> 1;

    result_bytes = 2 * FormatMessageW (
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_ALLOCATE_BUFFER,
        NULL,
        dwErrorCode,
        LANG_SYSTEM_DEFAULT,
        (LPWSTR)&tmp,
        0,
        NULL
    );    

    if (result_bytes == 0) {
        return -1;
    } 

    // FormatMessage's return is 1 character too short.
    result_bytes += 2;

    wcsncpy(lpResult, tmp, nchars);
    lpResult[nchars - 1] = 0;
    LocalFree((HLOCAL)tmp);

    if (result_bytes <= dwBytes) {
        return 0;
    } else {
        return result_bytes * 2;
    }
}

inline version(GetErrorMessage.h):

内联版本(GetErrorMessage.h):

#ifndef GetErrorMessage_H 
#define GetErrorMessage_H 
#include <Windows.h>    

/***
 * returns 0 if there was enough space, size of buffer in bytes needed
 * to fit the result, if there wasn't enough space. -1 on error.
 */
static inline int GetErrorMessageA(DWORD dwErrorCode, LPSTR lpResult, DWORD dwBytes)
{    
    LPSTR tmp;
    DWORD result_len;

    result_len = FormatMessageA (
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_ALLOCATE_BUFFER,
        NULL,
        dwErrorCode,
        LANG_SYSTEM_DEFAULT,
        (LPSTR)&tmp,
        0,
        NULL
    );        

    if (result_len == 0) {
        return -1;
    }

    // FormatMessage's return is 1 character too short.
    ++result_len;

    strncpy(lpResult, tmp, dwBytes);

    lpResult[dwBytes - 1] = 0;
    LocalFree((HLOCAL)tmp);

    if (result_len <= dwBytes) {
        return 0;
    } else {
        return result_len;
    }
}

/***
 * returns 0 if there was enough space, size of buffer in bytes needed
 * to fit the result, if there wasn't enough space. -1 on error.
 */
static inline int GetErrorMessageW(DWORD dwErrorCode, LPWSTR lpResult, DWORD dwBytes)
{   
    LPWSTR tmp;
    DWORD nchars;
    DWORD result_bytes;

    nchars = dwBytes >> 1;

    result_bytes = 2 * FormatMessageW (
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_ALLOCATE_BUFFER,
        NULL,
        dwErrorCode,
        LANG_SYSTEM_DEFAULT,
        (LPWSTR)&tmp,
        0,
        NULL
    );    

    if (result_bytes == 0) {
        return -1;
    } 

    // FormatMessage's return is 1 character too short.
    result_bytes += 2;

    wcsncpy(lpResult, tmp, nchars);
    lpResult[nchars - 1] = 0;
    LocalFree((HLOCAL)tmp);

    if (result_bytes <= dwBytes) {
        return 0;
    } else {
        return result_bytes * 2;
    }
}

#endif /* GetErrorMessage_H */

dynamic usecase(assumed that error code is valid, otherwise a -1 check is needed):

动态usecase(假设错误代码有效，否则需要-1检查):

#include <Windows.h>
#include <Winbase.h>
#include <assert.h>
#include <stdio.h>

int main(int argc, char **argv)
{   
    int (*GetErrorMessageA)(DWORD, LPSTR, DWORD);
    int (*GetErrorMessageW)(DWORD, LPWSTR, DWORD);
    char result1[260];
    wchar_t result2[260];

    assert(LoadLibraryA("GetErrorMessageLib.dll"));

    GetErrorMessageA = (int (*)(DWORD, LPSTR, DWORD))GetProcAddress (
        GetModuleHandle("GetErrorMessageLib.dll"),
        "GetErrorMessageA"
    );        
    GetErrorMessageW = (int (*)(DWORD, LPWSTR, DWORD))GetProcAddress (
        GetModuleHandle("GetErrorMessageLib.dll"),
        "GetErrorMessageW"
    );        

    GetErrorMessageA(33, result1, sizeof(result1));
    GetErrorMessageW(33, result2, sizeof(result2));

    puts(result1);
    _putws(result2);

    return 0;
}

regular use case(assumes error code is valid, otherwise -1 return check is needed):

常规用例(假定错误代码有效，否则需要-1返回检查):

#include <stdio.h>
#include "GetErrorMessage.h"
#include <stdio.h>

int main(int argc, char **argv)
{
    char result1[260];
    wchar_t result2[260];

    GetErrorMessageA(33, result1, sizeof(result1));
    puts(result1);

    GetErrorMessageW(33, result2, sizeof(result2));
    _putws(result2);

    return 0;
}

example using with assembly gnu as in MinGW32(again, assumed that error code is valid, otherwise -1 check is needed).

例如，在MinGW32中使用汇编gnu(同样，假设错误代码是有效的，否则需要-1检查)。

    .global _WinMain@16

    .section .text
_WinMain@16:
    // eax = LoadLibraryA("GetErrorMessageLib.dll")
    push $sz0
    call _LoadLibraryA@4 // stdcall, no cleanup needed

    // eax = GetProcAddress(eax, "GetErrorMessageW")
    push $sz1
    push %eax
    call _GetProcAddress@8 // stdcall, no cleanup needed

    // (*eax)(errorCode, szErrorMessage)
    push $200
    push $szErrorMessage
    push errorCode       
    call *%eax // cdecl, cleanup needed
    add $12, %esp

    push $szErrorMessage
    call __putws // cdecl, cleanup needed
    add $4, %esp

    ret $16

    .section .rodata
sz0: .asciz "GetErrorMessageLib.dll"    
sz1: .asciz "GetErrorMessageW"
errorCode: .long 33

    .section .data
szErrorMessage: .space 200

result: The process cannot access the file because another process has locked a portion of the file.

结果:进程无法访问文件，因为另一个进程锁定了文件的一部分。