SetErrorMode function (errhandlingapi.h)

Article
10/21/2021

Controls whether the system will handle the specified types of serious errors or whether the process will handle them.

Syntax

UINT SetErrorMode(
  [in] UINT uMode
);

Parameters

[in] uMode

The process error mode. This parameter can be one or more of the following values.

Value	Meaning
0	Use the system default, which is to display all error dialog boxes.
SEM_FAILCRITICALERRORS 0x0001	The system does not display the critical-error-handler message box. Instead, the system sends the error to the calling process. Best practice is that all applications call the process-wide SetErrorMode function with a parameter of SEM_FAILCRITICALERRORS at startup. This is to prevent error mode dialogs from hanging the application.
SEM_NOALIGNMENTFAULTEXCEPT 0x0004	The system automatically fixes memory alignment faults and makes them invisible to the application. It does this for the calling process and any descendant processes. This feature is only supported by certain processor architectures. For more information, see the Remarks section. After this value is set for a process, subsequent attempts to clear the value are ignored.
SEM_NOGPFAULTERRORBOX 0x0002	The system does not display the Windows Error Reporting dialog.
SEM_NOOPENFILEERRORBOX 0x8000	The OpenFile function does not display a message box when it fails to find a file. Instead, the error is returned to the caller. This error mode overrides the OF_PROMPT flag.

Return value

The return value is the previous state of the error-mode bit flags.

Remarks

Each process has an associated error mode that indicates to the system how the application is going to respond to serious errors. A child process inherits the error mode of its parent process. To retrieve the process error mode, use the GetErrorMode function.

Because the error mode is set for the entire process, you must ensure that multi-threaded applications do not set different error-mode flags. Doing so can lead to inconsistent error handling.

The system does not make alignment faults visible to an application on all processor architectures. Therefore, specifying SEM_NOALIGNMENTFAULTEXCEPT is not an error on such architectures, but the system is free to silently ignore the request. This means that code sequences such as the following are not always valid on x86 computers:

C++
SetErrorMode(SEM_NOALIGNMENTFAULTEXCEPT); fuOldErrorMode = SetErrorMode(0); ASSERT(fuOldErrorMode == SEM_NOALIGNMENTFAULTEXCEPT);

Itanium: An application must explicitly call SetErrorMode with SEM_NOALIGNMENTFAULTEXCEPT to have the system automatically fix alignment faults. The default setting is for the system to make alignment faults visible to an application.

Visual Studio 2005: When declaring a pointer to a structure that may not have aligned data, you can use the __unaligned keyword to indicate that the type must be read one byte at a time. For more information, see Windows Data Alignment.

Windows 7: Callers should favor SetThreadErrorMode over SetErrorMode since it is less disruptive to the normal behavior of the system.

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2003 [desktop apps \| UWP apps]
Target Platform	Windows
Header	errhandlingapi.h (include Windows.h)
Library	Kernel32.lib
DLL	Kernel32.dll