Parameter List

The optional Parameter-List defines the parameters that the caller passes to the procedure on the run-time stack.

Syntax

[, [LineBreak]] Parm-List

Parm-List:


Parm-Spec [, [LineBreak] Parm-Spec ...]

Parm-Spec:

Parameter-Name [:Type]

The introductory comma in front of the Parm-List is only required if a LineBreak is used to put the first Parm-Spec on the line following the PROC directive.

The optional LineBreak entry allows you to end a Parm-Spec entry with a comma, enter an optional EndOfLine-Comment followed by a physical NewLine character, then continue the Parm-List on the next line.

Remarks

Each Parameter-Name is defined as a Numeric-EquateName that is visible only from within the body of the procedure. The value assigned to the parameter name is an expression that defines the parameter type and its location on the stack relative to the value of the frame pointer (the BP or EBP register). The assembler automatically calculates the correct offset value based upon the size of the parameter type.

The Type field is specified as a Type-Declaration and defines the data type associated with the Parameter-Name. If this field is omitted, the data type defaults to WORD if the procedure is defined within a USE16 segment, and DWORD if the procedure is defined within a USE32 segment.

The programmer can read from and store into the locations defined by the Parm-Spec entries as though they were regular named variables, but if the parameter names are to be combined in indexed expressions with other registers, the normal rules for specifying BP- and EBP-relative expressions must be followed.

Example

This example defines a ReadBuffer procedure to accept four arguments passed on the stack.

        .386                      ; Assemble for 32-bit processors
        .model flat,syscall       ; OS/2 programming model/calling convention

        EXTERN DosRead:PROC       ; OS/2 DosRead() API
        INCLUDELIB os2386.lib     ; This lets us link to the API

        .code                     ; Open the code segment

;------------------------------------------------------------------------------
; Call operating system to read input into a buffer
;------------------------------------------------------------------------------
ReadBuffer PROC,                  ; need comma to continue the PROC statement
              hFile:dword,        ; parm 1: Read handle
              pBuffer:ptr byte,   ; parm 2: Address of input buffer
              cbRead:dword,       ; parm 3: Size of input buffer
              pulActual:ptr dword ; parm 4: Address of byte count from read

        ; set up to call the OS/2 DosRead entry point

        PUSH  pulActual           ; arg 4
        PUSH  cbRead              ; arg 3
        PUSH  pBuffer             ; arg 2
        PUSH  hFile               ; arg 1
        CALL  DosRead             ; Invoke syscall (SYSTEM) function
        ADD   ESP,DWORD * 4       ; Remove the four parameters we pushed
                                  ;   onto the stack for the DosRead call
        RET
ReadBuffer    ENDP

---

[Back: Register List]
[Next: LOCAL (Define Local Procedure Variables)]