This function determines the size of the header for the opened file. It sends MMIOM_QUERYHEADERLENGTH to the I/O procedure. The file was opened using mmioOpen.

#define INCL_MMIOOS2
#include <os2.h>

HMMIO    hmmio;           /*  Open file handle. */
PLONG    plHeaderLength;  /*  Size of the header. */
ULONG    ulReserved;      /*  Reserved. */
ULONG    ulFlags;         /*  Reserved. */
ULONG    rc;              /*  Return codes. */

rc = mmioQueryHeaderLength(hmmio, plHeaderLength,
       ulReserved, ulFlags);