DosGetCp

#define INCL_DOSNLS

USHORT  rc = DosGetCp(Length, CodePageList, DataLength);

USHORT           Length;        /* Length of list */
PUSHORT          CodePageList;  /* List (returned) */
PUSHORT          DataLength;    /* Length of list (returned) */

USHORT           rc;            /* return code */

Example 

This example gets the current code page and then up to 3 other prepared 
codepages. 

#define INCL_DOSNLS

USHORT CpList[8];
USHORT CpSize;
USHORT rc;

   rc = DosGetCp(sizeof(CpList),       /* Length of list */
                 CpList,               /* List */
                 &CpSize);             /* Length of returned list */