Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

◄Changes►                                             ◄Up► ◄Next► ◄Previous►
────────────────────────────────────────────────────────────────────────────
 
#define INCL_DOSMISC
 
USHORT DosSetVec(usVecNum, pfnFunction, ppfnPrev)
USHORT usVecNum;   /* type of exception                                   */
PFN pfnFunction;   /* pointer to function                                 */
PPFN ppfnPrev;     /* pointer to variable for previous function's address */
 
The DosSetVec function installs or removes an exception handler for a
specified exception. An exception is a program error, such as division by
zero, that causes the system to pass control to the exception handler. The
exception handler is an assembly-language routine that corrects errors or
cleans up programs before terminating. The system calls the exception
handler whenever the specified exception occurs. If a process does not
install its own exception handler, the default exception handler terminates
the process when an exception occurs.
 
The DosSetVec function is a family API function.
 
Parameter    Description
────────────────────────────────────────────────────────────────────────────
 
usVecNum     Specifies the number of the exception vector. This parameter
             can be one of the following values:
 
             Value                   Meaning
             ───────────────────────────────────────────────────────────────
             VECTOR_DIVIDE_BY_ZERO   Division by zero
 
             VECTOR_EXTENSION_ERROR  Processor extension error
 
             VECTOR_INVALIDOPCODE    Invalid operation code (opcode)
 
             VECTOR_NO_EXTENSION     Processor extension not available
 
             VECTOR_OUTOFBOUNDS      Out of bounds
 
             VECTOR_OVERFLOW         Overflow
 
pfnFunction  Points to the address of the exception handler that receives
             control when the specified exception occurs. If this parameter
             is zero, the DosSetVec function removes the current exception
             handler. For a full description, see the following "Comments"
             section.
 
ppfnPrev     Points to the variable that receives the address of the
             previous exception handler. The new exception handler can use
             this address to chain exception handling through all previous
             handlers or to restore the previous exception handler.
 
Return Value
 
The return value is zero if the function is successful. Otherwise, it is an
error value, which may be the following:
 
     ERROR_INVALID_FUNCTION
 
Comments
 
When the system calls the exception handler, it enables interrupts and
pushes the machine status word and far return address on the stack. If the
exception handler returns, it must use the iret (return-from-interrupt)
instruction.
 
If the DosSetVec function is used to install an exception handler for the
vector VECTOR_EXTENSION_ERROR, the function sets the machine status word to
indicate that no 80287 processor is available. The emulation bit is set and
the monitor-processor bit is cleared. (This is done without regard for the
true state of the hardware.) If the DosSetVec function is used to remove the
exception handler for VECTOR_EXTENSION_ERROR, the function sets the machine
status word to reflect the true state of the hardware.
 
If the routine being registered is in a segment that has the iopl
instruction indicated, the exception when it occurs, causes a general
protection fault and the process is terminated.
 
Restrictions
 
In real mode, the following restriction applies to the DosSetVec function:
 
♦  Because the 8086 and 8088 microprocessors do not raise this exception,
   usVecNum cannot be VECTOR_EXTENSION_ERROR.
 
See Also
 
DosDevConfig, DosError
 
                                      ♦