The diagnostic message is printed in wide characters. Thus, it will work as expected even if there are Unicode characters in the expression.

The destination of the diagnostic message depends on the type of application that called the routine. Console applications receive the message through **stderr**. In a Windows-based application, `assert` calls the Windows [MessageBox](/windows/win32/api/winuser/nf-winuser-messagebox) function to create a message box to display the message with three buttons: **Abort**, **Retry**, and **Ignore**. If the user clicks **Abort**, the program aborts immediately. If the user clicks **Retry**, the debugger is called and the user can debug the program if just-in-time (JIT) debugging is enabled. If the user clicks **Ignore**, `assert` continues with normal execution. Note that clicking **Ignore** when an error condition exists can result in undefined behavior.

To override the default behavior, the [`_set_error_mode`](set-error-mode.md) function can be used to select between the output-to-stderr and display-dialog-box behavior regardless of application type.

Since `assert` calls [`abort`](abort.md) immediately after displaying the message, the debug behavior for [`abort`](abort.md) will also occur. [`abort`](abort.md) will display a dialog box with the Abort, Retry, and Ignore buttons. This is not the same as the `assert` dialog box described above. In particular, [`abort`](abort.md) always exits the program during its execution, so neither the Retry nor Ignore button will resume execution following the `assert` call. The [`abort`](abort.md) dialog box is skipped if a dialog box was already displayed during `assert`, so this is only seen when output-to-stderr `assert` behavior is used.