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111 lines
3.9 KiB
Plaintext
111 lines
3.9 KiB
Plaintext
The [[MID$]] function returns a portion of a [[STRING|string]].
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{{PageSyntax}}
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: {{Parameter|portion$}} = [[MID$]]({{Parameter|stringValue$}}, {{Parameter|startPosition%}}[, {{Parameter|bytes%}}])
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{{Parameters}}
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* {{Parameter|stringValue$}} can be any literal or variable non-empty [[STRING]] value. Use [[LEN]] to check the length of a string.
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* {{Parameter|startPosition%}} designates the non-zero position of the first character to be returned by the function.
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* {{Parameter|bytes%}} (optional) tells the function how many characters to return including the first character at {{Parameter|startPosition%}}.
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{{PageDescription}}
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* When the {{Parameter|bytes%}} value is not passed, the function returns the remainder of the string from the starting character position.
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* Number of character {{Parameter|bytes%}} should be within the string's [[LEN|length]] from the start position, but will only return the string's remainder when exceeded.
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* If the {{Parameter|bytes%}} value is 0 or the {{Parameter|startPosition%}} is 0 or greater than the [[LEN|length]] of the string, an empty string is returned (no error is triggered).
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* In '''QB64''', [[ASC]] string byte position reads are about '''5 times faster''' than MID$ when parsing strings. See ''Example 2'' below.
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==QBasic/QuickBASIC==
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* In QBasic the {{Parameter|startPosition%}} could not be zero (0) or an [[ERROR Codes|Illegal function call error]] would occur.
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{{PageExamples}}
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''Example 1:'' Getting the hour and minutes from [[TIME$]]
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{{CodeStart}} '' ''
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{{Cl|PRINT}} {{Cl|TIME$}}
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hour$ = {{Cl|LEFT$}}({{Cl|TIME$}}, 2)
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minutes$ = {{Cl|MID$}}({{Cl|TIME$}}, 4, 2) ' skip hours and the colon (first 3 characters)
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{{Cl|PRINT}} "hour = "; hour$; ": minutes = "; minutes$ '' ''
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{{CodeEnd}}
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{{OutputStart}}11:23:30
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hour = 11: minutes = 23
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{{OutputEnd}}
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''Example 2:'' Comparing MID$, the '''QB64''' byte position version of [[ASC]] and [[_MEMGET]] speeds parsing string characters:
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{{CodeStart}} '' ''
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{{Cl|_TITLE}} "String Speed Test"
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{{Cl|DEFLNG}} A-Z
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'First let's build a string for testing.
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Limit = 100000 'the size of the string
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LoopCount = 1000 'the number of times we want to deconstruct it
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{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
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t$ = t$ + {{Cl|CHR$}}({{Cl|RND}} * 255)
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{{Cl|NEXT}}
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'now for some times
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t1# = {{Cl|TIMER}}
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{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
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{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
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m$ = {{Cl|MID$}}(t$, i, 1)
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{{Cl|NEXT}}
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{{Cl|NEXT}}
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t2# = {{Cl|TIMER}}
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{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
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{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
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m = {{Cl|ASC}}(t$, i)
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{{Cl|NEXT}}
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{{Cl|NEXT}}
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t3# = {{Cl|TIMER}}
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{{Cl|$CHECKING}}:OFF
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{{Cl|DIM}} m {{Cl|AS}} {{Cl|_MEM}}, m1 {{Cl|AS}} {{Cl|STRING}} * 1, m2 {{Cl|AS}} {{Cl|_UNSIGNED}} {{Cl|_BYTE}}
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m = {{Cl|_MEMNEW}}(Limit) 'create new memory space for string
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{{Cl|_MEMPUT}} m, m.OFFSET, t$ 'put string t$ into memory space
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{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
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{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
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{{Cl|_MEMGET}} m, m.OFFSET + i - 1, m1
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{{Cl|NEXT}}
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{{Cl|NEXT}}
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t4# = {{Cl|TIMER}}
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{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
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{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
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{{Cl|_MEMGET}} m, m.OFFSET + i - 1, m2
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{{Cl|NEXT}}
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{{Cl|NEXT}}
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t5# = {{Cl|TIMER}}
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'results
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{{Cl|PRINT USING}} "##.###### seconds for MID$"; t2# - t1#
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{{Cl|PRINT USING}} "##.###### seconds for ASC"; t3# - t2#
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{{Cl|PRINT USING}} "##.###### seconds for _MEMGET String"; t4# - t3#
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{{Cl|PRINT USING}} "##.###### seconds for _MEMGET Byte"; t5# - t4# '' ''
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{{CodeEnd}} {{small|Code by Steve McNeill}}
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{{OutputStart}}6.593750 seconds for MID$
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1.044922 seconds for ASC
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0.494141 seconds for _MEMGET String
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0.494141 seconds for _MEMGET Byte
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{{OutputEnd}}
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: ''Note:'' [[_MEMGET]] can be used with [[$CHECKING]]:OFF to cut the parsing speed even more. [[STRING]] * 1 or [[_BYTE]] are similar speeds.
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''See also:''
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* [[MID$ (statement)]], [[ASC]]
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* [[LEFT$]], [[RIGHT$]]
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* [[LTRIM$]], [[RTRIM$]]
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* [[INSTR]], [[LEN]]
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* [[_MEMPUT]], [[_MEMGET]]
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{{PageNavigation}}
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