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72 lines
2.7 KiB
Text
72 lines
2.7 KiB
Text
[[DEF SEG]] is used to define the area in memory to access QB64's emulated conventional memory.
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==Legacy support==
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* '''QB64 implements memory access using [[_MEM]] and related functions. For that reason, [[DEF SEG]] isn't recommended practice anymore and is supported to maintain compatibility with legacy code.'''
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{{PageSyntax}}
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: [[DEF SEG]] [=][{segment|VARSEG(variable}]
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{{PageDescription}}
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* Used to set the pointer to a memory area of a variable/array or register.
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* [[PEEK]] and [[POKE]] require a segment memory address (often just 0) without using VARSEG.
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* Important segments using [[PEEK]] and [[POKE]] include &HB800 (text segment) and &HA000 (graphics segment).
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* [[BSAVE]] and [[BLOAD]] require a VARSEG reference to the grahic array(0 index) used.
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* Always use DEF SEG when the procedure is completed, in order to reset the segment to QBasic's default value.
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* [[DEF SEG]], [[VARSEG]], [[VARPTR]], [[PEEK]] and [[POKE]] access QB64's emulated 16 bit conventional memory block. '''It is highly recommended to use QB64's [[_MEM]] memory system to avoid running out of memory.'''
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<!--
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{{PageExamples}}
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''Example:'' In a Qbasic(ONLY) file delete, '''SEG''' forces the parameter to be passed as a far pointer.
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{{CodeStart}} '' ''
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{{Cl|CONST}} file = "trashme.tmp" 'example temporary file name to delete
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{{Cl|DEFINT}} A-Z
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{{Cl|DIM}} filename {{Cl|AS}} {{Cl|STRING}}
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{{Cl|DIM}} result {{Cl|AS}} {{Cl|LONG}}
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{{Cl|DIM}} t {{Cl|AS}} {{Cl|STRING}}
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{{Cl|DIM}} i {{Cl|AS}} {{Cl|INTEGER}}
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{{Cl|CONST}} codelen = 48
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{{Cl|DIM}} code {{Cl|AS}} {{Cl|STRING}} * codelen
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{{Cl|CLS}}
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t = "5589E51E8B560C8EDA8B5E0A8B5702B441CD218B56088EDA8B5E06720B6631C0"
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t = t + "6689071F5DCA0800660D0000FFFFEBF0"
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{{Cl|FOR...NEXT|FOR}} i = 0 {{Cl|TO}} codelen - 1
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{{Cl|MID$}}(code, i + 1, 1) = {{Cl|CHR$}}({{Cl|VAL}}("&h" + {{Cl|MID$}}(t, i + i + 1, 2)))
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{{Cl|NEXT}}
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{{Cl|OPEN}} file {{Cl|FOR...NEXT|FOR}} {{Cl|APPEND}} {{Cl|AS}} 1 'create temporary file
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{{Cl|PRINT (file statement)|PRINT}} #1, "I am doomed! :-("
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{{Cl|CLOSE}}
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{{Cl|PRINT}} "now you see it:"
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{{Cl|SHELL}} "dir " + file
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K$ = {{Cl|INPUT$}}(1)
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filename = file + {{Cl|CHR$}}(0) 'create zero string name for DOS
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{{Cl|DEF SEG}} = {{Cl|VARSEG}}(code)
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{{Cl|CALL}} absolute('''SEG''' filename, '''SEG''' result, {{Cl|VARPTR}}(code))
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{{Cl|IF...THEN|IF}} result {{Cl|THEN}} 'check results
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{{Cl|PRINT}} "oops. error: 0x"; {{Cl|HEX$}}(result {{Cl|AND (boolean)|AND}} {{Cl|&H}}FFFF&)
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{{Cl|ELSE}}
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{{Cl|PRINT}} "now you don't:"
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{{Cl|END IF}}
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{{Cl|SHELL}} "dir " + file
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{{Cl|END}} '' ''
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{{CodeEnd}}
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{{small|Code by Michael Calkins as Public Domain(2011)}}
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-->
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''See also:''
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* [[DEF SEG = 0]]
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* [[VARPTR]], [[VARSEG]]
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* [[PEEK]], [[POKE]]
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* [[BSAVE]], [[BLOAD]]
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{{PageNavigation}}
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