I have a problem using a third-party component in Delphi 2006 (also Delphi 7), in which I get an «Unspecified Error» when executing a function call to that component. Do you have example code that utilises GetLastError and FormatMessage in Delphi, that would allow me to access more information about the error ? TIA 
asked Mar 21, 2009 at 10:10
3
There is an integrated helper function in Delphi: SysErrorMessage. It’s essentially a wrapper to FormatMessage, but much simpler to use in your case. Just provide the error code you need a textual description for.
For example you can use this to display the last error:
ShowMessage(SysErrorMessage(GetLastError))
If you want to raise an exception with this message, it’s even simpler:
RaiseLastOSError;
Important: Make sure that there is no additional API call between the failing function and your call of GetLastError, otherwise the last error will be reset.
Grim
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answered Mar 21, 2009 at 10:31
Daniel RikowskiDaniel Rikowski
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1
While DR is correct, there is a problem with this approach: It does not allow you to specify the context in which the error occurred. Ever seen the error «An API function failed.» whithout being any wiser which function it was and where it happended?
That’s why I wrote the RaiseLastOsErrorEx and Win32CheckEx functions:
procedure RaiseLastOsErrorEx(const _Format: string);
begin
RaiseLastOsErrorEx(GetLastError, _Format);
end;
procedure RaiseLastOsErrorEx(_ErrorCode: integer; _Format: string); overload;
var
Error: EOSError;
begin
if _ErrorCode <> ERROR_SUCCESS then
Error := EOSError.CreateFmt(_Format, [_ErrorCode, SysErrorMessage(_ErrorCode)])
else
Error := EOsError.CreateFmt(_Format, [_ErrorCode, _('unknown OS error')]);
Error.ErrorCode := _ErrorCode;
raise Error;
end;
function GetLastOsError(out _Error: string; const _Format: string = ''): DWORD;
begin
Result := GetLastOsError(GetLastError, _Error, _Format);
end;
function GetLastOsError(_ErrCode: integer; out _Error: string; const _Format: string = ''): DWORD;
var
s: string;
begin
Result := _ErrCode;
if Result <> ERROR_SUCCESS then
s := SysErrorMessage(Result)
else
s := _('unknown OS error');
if _Format <> '' then
try
_Error := Format(_Format, [Result, s])
except
_Error := s;
end else
_Error := s;
end;
function Win32CheckEx(_RetVal: BOOL; out _ErrorCode: DWORD; out _Error: string;
const _Format: string = ''): BOOL;
begin
Result := _RetVal;
if not Result then
_ErrorCode := GetLastOsError(_Error, _Format);
end;
(They are part of unit u_dzMiscUtils of my dzLib library available here:
https://osdn.net/projects/dzlib-tools/svn/view/dzlib/trunk/src/u_dzMiscUtils.pas?view=markup&root=dzlib-tools#l313
answered Jul 13, 2009 at 7:30
dummzeuchdummzeuch
11k4 gold badges51 silver badges159 bronze badges
4
Функция GetLastError возвращает код последней возникшей в системе ошибки, которая устанавливается при вызове функций API Windows. Для того, чтобы получить текст ошибки, соответствующий коду, в Delphi можно воспользоваться функцией FormatMessage из модуля Windows.
Данная функция имеет следующий прототип:
function FormatMessage(dwFlags: DWORD; lpSource: Pointer; dwMessageId: DWORD; dwLanguageId: DWORD; lpBuffer: PChar; nSize: DWORD; Arguments: Pointer): DWORD; stdcall;
Если функции FormatMessage передать параметры GetLastError в качестве идентификатора ошибки и LPCTSTR, то она вернет текст ошибки в локализованном формате.
Ниже приведен пример кода, который получает последнюю ошибку в системе и выводит ее текст в диалоговое окно:
var LastError: DWORD; ErrorMessage: array[0..MAX_PATH] of Char;begin LastError := GetLastError; if LastError <> ERROR_SUCCESS then begin FormatMessage( FORMAT_MESSAGE_FROM_SYSTEM, nil, LastError, LANG_USER_DEFAULT, ErrorMessage, MAX_PATH, nil ); ShowMessage(ErrorMessage); end;end;
В данном примере мы используем функцию GetLastError, чтобы получить код последней ошибки, а затем передаем его в функцию FormatMessage, чтобы получить текст ошибки. Полученный текст выводится в диалоговое окно функцией ShowMessage.
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Use GetLastError function to get code of the last error and SysErrorMessage function to convert this code to string.
procedure TForm1.Button1Click(Sender: TObject);
begin
ShowMessage(SysErrorMessage(GetLastError));
end;
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VIB
(2002-10-01 13:32)
[0]
Подскажите как из Delphi получить сообщение об ошибке код которой
генерирует функция GetLastError().
Мы используем функцию FormatMessage() но что-то не получается.
Если можно фрагмент кода.
Заранее благодарен.
← →
MBo
(2002-10-01 14:16)
[1]
var ErrStr:Pchar;
FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER or FORMAT_MESSAGE_FROM_SYSTEM,
nil,GetLastError,LANG_USER_DEFAULT,@ErrStr,0,nil);
Caption:=ErrStr;
← →
VIB
(2002-10-01 14:49)
[2]
Большое спасибо MBo все получилось.
← →
SPeller
(2002-10-01 21:19)
[3]
2 MBo © (01.10.02 14:16)
А освобождать строку не надо?
← →
Юрий Зотов
(2002-10-01 22:24)
[4]
Посмотрите также RaiseLastWin32Error и Win32Check. Во многих случаях упрощают дело.
← →
Pat
(2002-10-01 22:35)
[5]
SysErrorMessage(GetLastError)
Author: Embarcadero USA
Technical Information Database
TI2459C.txt Displaying an error string from GetLastError.
Category :General
Platform :All
Product :Borland C++ All
Description:
Displaying an Error Message with GetLastError
GetLastError is a WIN32 API that returns an error code indicating
the most recent error. The most recent error will be set by the
failing function. For example, if a call to LoadLibrary fails,
LoadLibrary will call SetLastError. The error code returned by
GetLastError can be found in WINERROR.H but another WIN32 API,
FormatMessage, has built-in support for retrieving an appropriate
error message string.
FormatMessage is used to build up a message string given a number of
options such as language. The source for the message can be a buffer
or string resource found within a module. Additionally, FormatMessage
supports a flag that will read the string from an operating system
message table. The necessary flag is FORMAT_MESSAGE_FROM_SYSTEM.
The following sample demonstrates using FormatMessage to allocate
and fill a buffer with the most recent error ( returned by a call
to GetLastError ). This example was built as a console mode application
with the command line:
bcc32 test.cpp
Of course, in a WIN32 GUI application the buffer could be used in a
call to MessageBox.
#include
#include
int main()
{
LPVOID ptr = 0;
// try a sure-to-fail API call such as one of the following
LoadLibrary("sijvoaisjv"); // "library file...cannot be found"
// LoadLibrary((char*)1234); // "The parameter is incorrect"
FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM,
NULL,
GetLastError(),
MAKELANGID( LANG_ENGLISH, SUBLANG_ENGLISH_US ),
(LPTSTR)&ptr,
0, NULL);
cout <<
Article originally contributed by Borland Staff