Except as noted, the information in this section applies to both Explorer-style and old-style Open and Save As dialog boxes.
The dialog box automatically validates filenames typed by the user to ensure that the names contain only valid characters. To override the filename character validation, set the OFN_NOVALIDATE flag.
To force the dialog box to verify that the user specified the name of an existing file, set the OFN_FILEMUSTEXIST flag. To force verification that the specified path exists, set the OFN_PATHMUSTEXIST flag. If you set the OFN_CREATEPROMPT flag, the dialog box prompts the user for permission to create a nonexistent file. If this flag is set and the user chooses to create a new file, the dialog box closes, and the function returns the specified name. Otherwise, the dialog box remains open.
When using the Save As dialog box, you can direct the dialog box to prompt the user for permission to overwrite an existing file by setting the OFN_OVERWRITEPROMPT flag.
By default, the dialog box creates a zero-length test file to determine whether a new file can be created in the selected directory. To prevent the creation of this test file, set the OFN_NOTESTFILECREATE flag.
If you enable a hook procedure, the dialog box notifies your hook procedure when a network sharing violation occurs for the filename specified by the user. If you set the OFN_EXPLORER flag, the dialog box sends the CDN_SHAREVIOLATION message to the hook procedure. If you do not set OFN_EXPLORER, the dialog box sends the SHAREVISTRING registered message to the hook procedure. To prevent the dialog box from sending any notifications for sharing violations, set the OFN_SHAREAWARE flag.
If the user selects the read-only check box, the dialog box sets the OFN_READONLY flag on return. To hide the Open As Read Only check box, set the OFN_HIDEREADONLY flag. To prevent the dialog box from returning names of existing files that have the read-only attribute, set the OFN_NOREADONLYRETURN flag.
To prevent the dialog box from dereferencing link files, set the OFN_NODEREFERENCELINKS value. In this case, the dialog box returns the name of the link file rather than the name of the file referenced by the link file.