LW549
The nth position of the specified sub-string in the string is obtained, the efficiency is not high, and it is barely available. I feel interest, so I try to try it. The program is attached to the end, here is some explanations: 1, for quick write, no use of console methods should be used, but use the GUI mode; 2, the sample sample is to find a string containing four substrings , Check four locations separately. This is done in the Button1Click method. It calls Tests to perform specific tests to measure functions, the second appearance, the number of cycles is parameters; 3. Tests repeats each specific function in one cycle, at the same time for fair (Perhaps the previous function is a latted road-memory, high-speed buffer), this test is test_count, and finally outputs the average time each time; 4, after the early test, the LW549 code is not high, So give it a small number of cycles (one thousand times), so as not to cause the programs to be killed; other three thousand; The POSEX function added in Delphi 7; POSN_STRPOS: Use the StrPos function. Program output:
Search "Function Getnstringpos (N: Integer; Substring, Astring: String): Integer;" for "string"
1:
Substr Index: 1; Loop Count = 1000
Getnstringpos: Return 17; TIMING: 37.60 MS
Substr Index: 1; Loop Count = 100000
POSN_POS: RETURN 17; TIMING: 40.40 ms
POSN_POSEX: RETURN 17; TIMING: 15.60 MS
POSN_STRPOS: RETURN 22; TIMING: 37.80 MS
2:
Substr Index: 2; Loop Count = 1000
Getnstringpos: Return 42; TIMING: 96.80 MS
Substr Index: 2; Loop Count = 100000
POSN_POS: RETURN 42; TIMING: 81.20 MS
POSN_POSEX: RETURN 42; TIMING: 47.00 MS
POSN_STRPOS: RETURN 47; TIMING: 53.00 MS
3:
Substr Index: 3; Loop Count = 1000
Getnstringpos: Return 50; TIMING: 109.40 MS
Substr Index: 3; Loop Count = 100000
POSN_POS: Return 50; TIMING: 118.80 MS
POSN_POSEX: RETURN 50; TIMING: 53.00 MS
POSN_STRPOS: RETURN 55; TIMING: 62.60 MS
4:
Substr Index: 4; Loop Count = 1000
Getnstringpos: Return 58; TIMING: 128.20 MS
Substr Index: 4; Loop Count = 100000
POSN_POS: RETURN 58; TIMING: 162.60 MS
POSN_POSEX: RETURN 58; TIMING: 59.40 MS
POSN_STRPOS: RETURN 63; TIMING: 74.80 MS It can be seen that the results of the test (efficiency) are: POSN_POSEX> POSN_STRPOS> POSN_POS >> GetnsUbstringPOS. I have expected that POSN_STRPOS is most powerful, but the result is not. It is estimated that POSEX optimization is relatively powerful. Access code:
Unit1.pas:
Unit unit1;
Interface
Uses
Windows, Messages, Sysutils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, Stdctrls, DB, DBTABLES;
Type
Tposnfunc = function (n: integer; const Substring, Astring: String): Integer;
Type
TFORM1 = Class (TFORM)
Memo1: TMEMO;
Button1: tbutton;
Procedure Button1Click (Sender: TOBJECT);
Procedure formcreate (Sender: TOBJECT);
Private
Procedure Tests (Const Funcs: array of tposnfunc
Const funcnames: array of string; istr: integer; loopcount: integer;
public
END;
VAR
FORM1: TFORM1;
IMPLEMentation
Uses
Strustils;
{$ R * .dfm}
Function GetnstringPOS (N: Integer; Substring, Astring: String): Integer;
/ / Return the location of the nth subString appears in Astring
// If you didn't find it, return -1
VAR
FINDCOUNT: Integer;
POS: integer;
Begin
RESULT: = -1;
POS: = 0;
For FINDCOUNT: = 1 to n Do Begin
INC (POS);
While Midstr (Astring, Pos, Length (Substring) <> Substring Do Begin
If Length (Astring) Exit; // Not found INC (POS); END; END; Result: = POS; END; Function POSN_POS (N: Integer; Substring, Astring: String): Integer; VAR p: integer; NSUB: Integer; NSRC: Integer; Begin NSUB: = Length (Substring); NSRC: = Length (astring); Result: = -nsub; While n> 0 do Begin P: = POS (Substring, Astring); IF P = 0 THEN Break; DEC (n); INC (Result, P NSUB); Astring: = COPY (Astring, P NSUB 1, NSRC-NSUB-P-1); DEC (NSRC, NSUB P); END; IF n> 0 THEN RESULT: = -1; END; Function POSN_POSEX (N: Integer; Substring, Astring: String): Integer; Var p: integer; NSUB: Integer; Begin NSUB: = Length (Substring); Result: = 0; P: = 0; While n> 0 do Begin P: = posex (Substring, Astring, P 1); IF P = 0 THEN Break; DEC (n); Result: = P; INC (P, NSUB); END; IF n> 0 THEN RESULT: = -1; END; Function POSN_STRPOS (N: Integer; Substring, Astring: String): Integer; VAR PSUB, PSRC, P: PCHAR; NSUB: Integer; Begin NSUB: = Length (Substring); PSUB: = PCHAR (SUBSTRING); PSRC: = PCHAR (Astring); p: = psrc; While (n> 0) DO Begin P: = Strpos (P, PSUB); IF (p = nil) THEN Break; INC (P, NSUB); DEC (n); END; IF (n = 0) AND (P <> nil) THEN Result: = P - PSRC Else Result: = 0; END; Const Str = 'Function GetnstringPOS (N: Integer; Substring, Astring: String): Integer;'; Substr = 'String'; TEST_COUNT = 5; Procedure TFORM1.TESTS (Const Funcs: array of tposnfunc; Const funcnames: array of string; Istr: integer; LoopCount: integer; VAR I, J, K: Integer; TM: longword; Func: tposnfunc; Count: integer; RETV: ARRAY OF INTEGER; Results: array of longword; Begin Count: = Length (FUNCS); Assert (count = length (funcnames)); Memo1.Lines.Add (Format ('Substr Index:% D; Loop Count =% D', [istr, loopcount]); SETLENGTH (RETV, COUNT); SetLENGTH (RESUNT); For j: = 0 to count-1 do RESULTS [J]: = 0; Fork: = 1 to test_count do Begin For j: = 0 to count-1 do Begin Func: = funcs [j]; TM: = GettickCount; For i: = 1 to loopcount do RETV [J]: = FUNC (ISTR, SUBSTR, STR); INC (Results [J], GettickCount - TM); END; END; For j: = 0 to count-1 dobegin Memo1.Lines.Add (Format ('% s: return% D; TIMING:% N MS', [FuncNames [J], RETV [J], Results [J] * 1.0 / Test_count])) END; END; Procedure TFORM1.BUTTON1CLICK (Sender: TOBJECT); VAR i: integer; Begin For i: = 1 to 4 do Begin Memo1.Lines.Add (Format ('% d:', [i])); Tests ([@getnstringpos], ['getnstringpos'], i, 1000); Tests ([@POSN_POS, @POSN_POSEX, @POSN_STRPOS], ['POSN_POS', 'POSN_POSEX', 'POSN_STRPOS'], I, 100000); END; END; Procedure TFORM1.FormCreate (Sender: TOBJECT); Begin Memo1.clear; Memo1.Lines.Add (Format ('Search "% S" for "% s", [str, substr]); END; End. Unit1.dfm: Object Form1: TFORM1 LEFT = 243 TOP = 164 Width = 578 HEIGHT = 516 Alphablendvalue = 192 CAPTION = 'FORM1' Color = CLBTNFACE Font.charset = default_charset Font.color = CLWINDOWTEXT Font.height = -11 Font.name = 'MS SANS Serif' Font.style = [] OldcreateOrder = FALSE Position = Podefaultposonly Oncreate = formcreate DesignSize = 570 489) Pixelsperinch = 96 TEXTHEIGHT = 13 Object Memo1: TMEMO LEFT = 3 TOP = 32 Width = 565 HEIGHT = 457 Anchors = [Akleft, Aktop, Akright, Akbottom] Lines.strings = 'MEMO1') Scrollbars = SSVertical Taborder = 0 end Object Button1: TButton LEFT = 3 TOP = 6 Width = 75 HEIGHT = 25 CAPTION = 'Button1' Taborder = 1 Onclick = button1click end end
