DOS Interface

These routines are implemented as functions and declared in DOS.H.

The _dosexterr function obtains and stores the error information returned by DOS system call 0x59 (extended error handling). This function is provided for use with DOS versions 3.0 and later.

The _bdos routine is useful for invoking DOS calls that use either or both of the DX (DH/DL) and AL registers for arguments. However, _bdos should not be used to invoke system calls that return an error code in AX if the carry flag is set; since your program cannot detect whether the carry flag is set, it cannot determine whether the value in AX is a legitimate value or an error value. In this case, the _intdos routine should be used instead, since it allows the program to detect whether the carry flag is set. The _intdos routine can also be used to invoke DOS calls that use registers other than DX and AL.

The _intdosx routine is similar to the _intdos routine, but is used when ES is required by the system call, when DS must contain a value other than the default data segment (for instance, when a far pointer is used), or when making the system call in a large-model program. When calling _intdosx, give an argument that specifies the segment values to be used in the call.

The _int86 routine can be used to invoke any interrupt. The _int86x routine is similar; however, like the _intdosx routine, it is designed to work with large-model programs and far items, as described in the preceding paragraph.

The _FP_OFF and _FP_SEG routines allow easy access to the segment and offset portions of a far pointer value. _FP_OFF and _FP_SEG are implemented as macros and defined in DOS.H.

The _segread routine returns the current values of the segment registers. This routine is typically used with the _intdosx and _int86x routines to obtain the correct segment values.

The _chain_intr routine is useful for chaining interrupt handlers together. The _enable routine enables interrupts, while the _disable routine disables interrupts.

The routines prefixed with _dos_ are all direct system interfaces that use the system calls noted above. More detailed information on these system calls can be found in the MS-DOS Encyclopedia (Duncan, ed.; Redmond, WA: Microsoft Press, 1988) or the Programmer's PC Sourcebook 2nd ed. (Hogan; Redmond, WA: Microsoft Press, 1991).

Note:

The DOS interface I/O routines are generally incompatible with console, low-level, and stream I/O routines. Do not mix different types of I/O routines in the same source file.