mb_substitute_character()
specifies substitution character when input character
encoding is invalid or character code is not exist in output
character encoding. Invalid characters may be substituted NULL(no output), string or
integer value (Unicode character code value).
This setting affects
mb_detect_encoding() and
mb_send_mail().
substchar : Specify
Unicode value as integer or specify as string as follows
"none" : no output
"long" : Output character code value (Example:
U+3000,JIS+7E7E)
Return Value: If
substchar is set, it returns
TRUE for success, otherwise returns FALSE. If
substchar is not set, it returns Unicode value or
"none"/"long".