GetLastError is a number. What does it mean?
A customer asked
I'm getting an error 12 back from a GetLastError call, and I've seen a number of sites that tell me I can figure out what that error is by sending it to SysErrorMessage. But nothing I've seen shows how to declare SysErrorMessage. It doesn't appear to be in Kernal32 because I get an error if I try to DECLARE it there. Where does this API live?
Understanding an error number from GetLastError() is probably useful. If you have Visual Studio installed, these errors are defined in
C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\PlatformSDK\Include\WinError.h
For error 12, that files says:
//
// MessageId: ERROR_INVALID_ACCESS
//
// MessageText:
//
// The access code is invalid.
//
#define ERROR_INVALID_ACCESS 12L
You can also start VS and choose Tools->Error Lookup
I haven’t heard of the “SysErrorMessage” function and a search of MSDN turns up nothing. There are a few mentions of it from internet searches. Perhaps it is outdated.
To turn an error number into English text, you can use the FormatMessage function. A parameter specifies what language the string should be. For that, we call GetSystemDefaultLangID
#define FORMAT_MESSAGE_ALLOCATE_BUFFER 0x00000100
#define FORMAT_MESSAGE_IGNORE_INSERTS 0x00000200
#define FORMAT_MESSAGE_FROM_STRING 0x00000400
#define FORMAT_MESSAGE_FROM_HMODULE 0x00000800
#define FORMAT_MESSAGE_FROM_SYSTEM 0x00001000
#define FORMAT_MESSAGE_ARGUMENT_ARRAY 0x00002000
#define FORMAT_MESSAGE_MAX_WIDTH_MASK 0x000000FF
DECLARE integer GetSystemDefaultLangID IN win32api
DECLARE integer FormatMessage IN WIN32API integer dwFlags,;
integer lpSource,;
integer dwMessageId,;
integer dwLanguageId,;
string @ lpBuffer,;
integer nSize
langid=BITAND(0xffff,GetSystemDefaultLangID())
?TRANSFORM(langid,"@0x")
nErr=122
cstr=SPACE(1024)
nlen=FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, 0,nErr,langid, @cstr, LEN(cstr))
IF nlen>0
cErr=LEFT(cstr,nlen)
?"Message=",cErr
ENDIF
