Modifies __error_mode to determine a non-default location where the C run time writes an error message for an error that will possibly end the program.

int _set_error_mode(
   int modeval 


  • modeval
    Destination of error messages.

Return Value

Returns the old setting or -1 if an error occurs.


Controls the error output sink by setting the value of __error_mode. For example, you can direct output to standard error or use the MessageBox API.

The modeval parameter can be set to one of the following.




Error sink is determined by __app_type.


Error sink is a standard error.


Error sink is a message box.


Report the current __error_mode value.

If a value other than those listed above is passed in, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, _set_error_mode sets errno to EINVAL and returns -1.

When used with an assert, _set_error_mode displays the failed statement in the dialog box and give you the option of clicking Ignore, which allows you to continue executing the program.



Required header




// crt_set_error_mode.c
// compile with: /c
#include <stdlib.h>
#include <assert.h>

int main()
Assertion failed: 2+2==5, file crt_set_error_mode.c, line 8

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

See Also


assert (CRT)