c# - How does String.Contains work? -

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possible duplicate:
what algorithm .net use searching pattern in string?

i have loop in program gets line file. there check whether line contains string

if(line.contains("string")) {     //do other stuff }

there on 2 million rows in file if can quicken speed 1/10th millisecond save me on 3 minutes on each run.

so... line 1000 chars long, quicker short or long string, or not make difference?

line.contains("abcdefghijklmnopqrstuvwxyz");

or

line.contains("abcdefg")

thank in advance.

string.contains() follows torturous route through system.globalization.compareinfo clr , nls support sub-system thoroughly got lost. contains highly optimized code impressive perf. way faster through pinvoking standard crt function wcsstr, available in msvcrt.dll

    [dllimport("msvcrt.dll", charset = charset.unicode)]     private static extern intptr wcsstr(string tosearch, string tofind);

it returns intptr.zero if string wasn't found. made measurements, using string.indexof() instead of contains() test various string comparison options. times in nanoseconds, searching string of 7 characters in string of 60 characters. string not present worst case measured. lowest time out of sample of 20 used:

stringcomparison.ordinal (same contains) : 245 nanoseconds stringcomparison.ordinalignorecase : 327 stringcomparison.invariantculture : 251 stringcomparison.invariantcultureignorecase : 327 stringcomparison.currentculture : 275 stringcomparison.currentcultureignorecase : 340 wcsstr : 213

very impressive numbers , on par you'd expect these functions require. wcsstr() function same kind of ordinal comparison string.compare(). 13% faster, statistically insignificant improvement given real perf not approach these measurements due effects of cpu cache locality. can conclude you're going fast can expect. whether slight improvement wcsstr worth you.


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