When the fopen() function is used to open files , the default CCSID of the file is different depending on whether or not UTF support is used. If UTF support is not used (that is, if LOCALETYPE(*CLD), LOCALETYPE(*LOCALE), or LOCALETYPE(*LOCALEUCS2) are specified on the compilation command), the file CCSID defaults to the current job CCSID. Usually this works well because the job CCSID is set correctly and the current locale is set to match the job CCSID.
With UTF support, the job CCSID cannot be set to UTF-8 because of system limitations. When LOCALETYPE(*LOCALEUTF) is specified, the file CCSID defaults to the CCSID of the current locale. If the default locale is being used, the CCSID defaults to UTF-8 (CCSID 1208). If this default is not desired, the ccsid or o_ccsid keyword can be specified in the second parameter of the fopen() call. However, database files are an exception, because DB2® for i5/OS does not completely support UTF-8. When SYSIFCOPT(*NOIFSIO) is specified, and the CCSID of the current locale is 1208, the CCSID of the file defaults to CCSID 65535 (no conversion) rather than CCSID 1208. This allows CCSID 1208 to be used with database files. For more information about file CCSIDs, see fopen() — Open Files.