MID$ (function): Difference between revisions

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(Created page with "The MID$ function returns a portion of a string. {{PageSyntax}} : {{Parameter|portion$}} = MID$({{Parameter|stringValue$}}, {{Parameter|startPosition%}}[, {{Parameter|bytes%}}]) {{PageParameters}} * {{Parameter|stringValue$}} can be any literal or variable non-empty STRING value. Use LEN to check the length of a string. * {{Parameter|startPosition%}} designates the non-zero position of the first character to be returned by the function. * {...")
 
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The [[MID$]] function returns a portion of a [[STRING|string]].
The '''MID$''' function returns a portion of a [[STRING]].




{{PageSyntax}}
{{PageSyntax}}
: {{Parameter|portion$}} = [[MID$]]({{Parameter|stringValue$}}, {{Parameter|startPosition%}}[, {{Parameter|bytes%}}])
: {{Parameter|portion$}} = [[MID$ (function)|MID$]]({{Parameter|stringValue$}}, {{Parameter|startPosition%}}[, {{Parameter|bytes%}}])




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{{PageDescription}}
{{PageDescription}}
* When the {{Parameter|bytes%}} value is not passed, the function returns the remainder of the string from the starting character position.
* When the {{Parameter|bytes%}} value is not passed, the function returns the remainder of the string from the starting character position.
* 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.
* Number of character {{Parameter|bytes%}} should be within the string's length from the start position, but will only return the string's remainder when exceeded.
* 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).
* If the {{Parameter|bytes%}} value is 0 or the {{Parameter|startPosition%}} is 0 or greater than the length of the string, an empty string is returned (no error is triggered).
* In '''QB64''', [[ASC]] string byte position reads are about '''5 times faster''' than MID$ when parsing strings. See ''Example 2'' below.
* In '''QB64''', the [[ASC (function)]] reads string byte positions about 5 times faster than '''MID$''' when parsing strings character wise. See ''Example 2'' below.


=== QBasic/QuickBASIC ===
=== QBasic/QuickBASIC ===
Line 23: Line 23:


{{PageExamples}}
{{PageExamples}}
''Example 1:'' Getting the hour and minutes from [[TIME$]]
;Example 1:Getting the hour and minutes from [[TIME$]].
{{CodeStart}}
{{CodeStart}}
{{Cl|PRINT}} {{Cl|TIME$}}
{{Cl|PRINT}} {{Cl|TIME$}}


hour$ = {{Cl|LEFT$}}({{Cl|TIME$}}, 2)
hour$ = {{Cl|LEFT$}}({{Cl|TIME$}}, 2)
minutes$ = {{Cl|MID$}}({{Cl|TIME$}}, 4, 2) ' skip hours and the colon (first 3 characters)
minutes$ = {{Cl|MID$ (function)|MID$}}({{Cl|TIME$}}, 4, 2) ' skip hours and the colon (first 3 characters)


{{Cl|PRINT}} "hour = "; hour$; ": minutes = "; minutes$
{{Cl|PRINT}} "hour = "; hour$; ": minutes = "; minutes$
{{CodeEnd}}
{{CodeEnd}}
{{OutputStart}}11:23:30
{{OutputStart}}
11:23:30
hour = 11: minutes = 23
hour = 11: minutes = 23
{{OutputEnd}}
{{OutputEnd}}


----


''Example 2:'' Comparing MID$, the '''QB64''' byte position version of [[ASC]] and [[_MEMGET]] speeds parsing string characters:
Example 2:Comparing '''MID$''', the '''QB64''' byte position version of the [[ASC (function)]] and [[_MEMGET]] speeds parsing string characters.
{{CodeStart}}
{{CodeStart}}
{{Cl|_TITLE}} "String Speed Test"
{{Cl|_TITLE}} "String Speed Test"
Line 55: Line 57:
{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
   {{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
   {{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
     m$ = {{Cl|MID$}}(t$, i, 1)
     m$ = {{Cl|MID$ (function)|MID$}}(t$, i, 1)
   {{Cl|NEXT}}
   {{Cl|NEXT}}
{{Cl|NEXT}}
{{Cl|NEXT}}
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{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
{{Cl|FOR...NEXT|FOR}} j = 1 {{Cl|TO}} LoopCount
   {{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
   {{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} Limit
     m = {{Cl|ASC}}(t$, i)
     m = {{Cl|ASC (function)|ASC}}(t$, i)
   {{Cl|NEXT}}
   {{Cl|NEXT}}
{{Cl|NEXT}}
{{Cl|NEXT}}
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0.494141 seconds for _MEMGET Byte
0.494141 seconds for _MEMGET Byte
{{OutputEnd}}
{{OutputEnd}}
: ''Note:'' [[_MEMGET]] can be used with [[$CHECKING]]:OFF to cut the parsing speed even more. [[STRING]] * 1 or [[_BYTE]] are similar speeds.
;Note:[[_MEMGET]] can be used with [[$CHECKING]]:OFF to cut the parsing speed even more. [[STRING]] * 1 or [[_BYTE]] are similar speeds.




{{PageSeeAlso}}
{{PageSeeAlso}}
* [[MID$ (statement)]], [[ASC]]
* [[MID$]]
* [[ASC]], [[ASC (function)]]
* [[LEFT$]], [[RIGHT$]]
* [[LEFT$]], [[RIGHT$]]
* [[LTRIM$]], [[RTRIM$]]
* [[LTRIM$]], [[RTRIM$]]

Revision as of 00:40, 26 February 2023

The MID$ function returns a portion of a STRING.


Syntax

portion$ = MID$(stringValue$, startPosition%[, bytes%])


Parameters

  • stringValue$ can be any literal or variable non-empty STRING value. Use LEN to check the length of a string.
  • startPosition% designates the non-zero position of the first character to be returned by the function.
  • bytes% (optional) tells the function how many characters to return including the first character at startPosition%.


Description

  • When the bytes% value is not passed, the function returns the remainder of the string from the starting character position.
  • Number of character bytes% should be within the string's length from the start position, but will only return the string's remainder when exceeded.
  • If the bytes% value is 0 or the startPosition% is 0 or greater than the length of the string, an empty string is returned (no error is triggered).
  • In QB64, the ASC (function) reads string byte positions about 5 times faster than MID$ when parsing strings character wise. See Example 2 below.

QBasic/QuickBASIC


Examples

Example 1
Getting the hour and minutes from TIME$.
PRINT TIME$

hour$ = LEFT$(TIME$, 2)
minutes$ = MID$(TIME$, 4, 2) ' skip hours and the colon (first 3 characters)

PRINT "hour = "; hour$; ": minutes = "; minutes$

11:23:30
hour = 11: minutes = 23

Example 2:Comparing MID$, the QB64 byte position version of the ASC (function) and _MEMGET speeds parsing string characters. 

_TITLE "String Speed Test"
DEFLNG A-Z

'First let's build a string for testing.
Limit = 100000 'the size of the string
LoopCount = 1000 'the number of times we want to deconstruct it

FOR i = 1 TO Limit
  t$ = t$ + CHR$(RND * 255)
NEXT

'now for some times

t1# = TIMER
FOR j = 1 TO LoopCount
  FOR i = 1 TO Limit
    m$ = MID$(t$, i, 1)
  NEXT
NEXT
t2# = TIMER
FOR j = 1 TO LoopCount
  FOR i = 1 TO Limit
    m = ASC(t$, i)
  NEXT
NEXT

t3# = TIMER
$CHECKING:OFF
DIM m AS _MEM, m1 AS STRING * 1, m2 AS _UNSIGNED _BYTE
m = _MEMNEW(Limit) 'create new memory space for string
_MEMPUT m, m.OFFSET, t$ 'put string t$ into memory space
FOR j = 1 TO LoopCount
  FOR i = 1 TO Limit
    _MEMGET m, m.OFFSET + i - 1, m1
  NEXT
NEXT
t4# = TIMER
FOR j = 1 TO LoopCount
  FOR i = 1 TO Limit
    _MEMGET m, m.OFFSET + i - 1, m2
  NEXT
NEXT
t5# = TIMER

'results

PRINT USING "##.###### seconds for MID$"; t2# - t1#
PRINT USING "##.###### seconds for ASC"; t3# - t2#
PRINT USING "##.###### seconds for _MEMGET String"; t4# - t3#
PRINT USING "##.###### seconds for _MEMGET Byte"; t5# - t4#
Code by Steve McNeill
6.593750 seconds for MID$
1.044922 seconds for ASC
0.494141 seconds for _MEMGET String
0.494141 seconds for _MEMGET Byte
Note
_MEMGET can be used with $CHECKING:OFF to cut the parsing speed even more. STRING * 1 or _BYTE are similar speeds.


See also


Navigation:
Main Page with Articles and Tutorials
Keyword Reference - Alphabetical
Keyword Reference - By usage
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