Microsoft KB Archive/111877

= BUG: SIZE and SIZEOF May Give Incorrect Values for Locals =

Article ID: 111877

Article Last Modified on 10/14/2003

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APPLIES TO


 * Microsoft Macro Assembler 6.0 Standard Edition
 * Microsoft Macro Assembler 6.0a
 * Microsoft Macro Assembler 6.0b
 * Microsoft Macro Assembler 6.1 Standard Edition
 * Microsoft Macro Assembler 6.1a
 * Microsoft Macro Assembler 6.11 Standard Edition

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This article was previously published under Q111877



SYMPTOMS
SIZEOF and SIZE drop the high byte of the size for LOCAL variables larger than 255 bytes. The SIZE and SIZEOF for global variables and data types is correct. The TYPE operator works correctly for all variables.



RESOLUTION
You can use the TYPE and LENGTHOF operators to obtain the correct size of local variables.



STATUS
Microsoft has confirmed this to be a problem in MASM versions 6.x. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.



MORE INFORMATION
In the following example, structure junk1 is 255 bytes and junk2 is 256 bytes. If local variables are used, SIZE and SIZEOF return 0 (zero) for the size of the local variable j2L. This can be seen in the listing file or in CodeView if the program is run in the debugger. Note that the TYPE operator works correctly for single-element variables. To find the size of array types, use TYPE * LENGTHOF as shown for j3L below.

Sample Code
; assembly options needed: /Zi /Fl /Sa .model large,c .386 junktest PROTO junk1 struct a BYTE 255 DUP (?) junk1 ends

junk2 struct a BYTE 256 DUP (?) junk2 ends

.stack 10000 .data j1 junk1 <> j2 junk2 <>

.CODE .STARTUP mov ax, sizeof junk1 ; correct sizes here mov ax, sizeof j1       mov ax, size j1        mov ax, sizeof junk2 mov ax, sizeof j2       mov ax, size j2        invoke junktest .EXIT

junktest PROC LOCAL j1L:junk1    ; correct amount allocated 255 bytes LOCAL j2L:junk2    ; correct amount allocated 256 bytes LOCAL j3L[256]:BYTE ; correct amount allocated 256 bytes

mov ax,0 mov ax, sizeof junk1 ; correct -- 0FFh mov ax, sizeof j1L  ; correct -- 0FFh mov ax, size j1L    ; correct -- 0FFh mov ax, type j1L    ; correct -- 0FFh mov ax, sizeof junk2 ; correct -- 0100h mov ax, sizeof j2L  ; high byte lost -- returns 00h mov ax, size j2L    ; high byte lost -- returns 00h mov ax, type j2L    ; OK -- returns 0100h mov ax, sizeof j3L  ; high byte lost -- returns 00h mov ax, size j3L    ; high byte lost -- returns 00h mov ax, type j3L * lengthof j3L ; OK - returns 0100h ret junktest ENDP

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Additional query words: 6.00 6.00a 6.00b 6.10 6.10a 6.10b 6.11 ml buglist6.11

Keywords: KB111877

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