c# - Foreach loop - performance with long string -


i'm facing problem performance in c# application. problem quite long string - base64 coded, not ordinary. characters has moved 5 characters , odd ones 5 characters down, create readable base64 string. heres code:

string b64stock; // <- long 1 int b = 0; string b64readable = ""; foreach (char c in b64stock)         {             if ((b % 2) == 0)             {                 int asciichar = (int)c;                 asciichar += 5;                 b64readable += (char)asciichar;             }             else             {                 int asciichar = (int)c;                 asciichar -= 5;                 b64readable += (char)asciichar;             }             b++;         }

i checked code stopwatch. takes 17 seconds, execute loop. steps should take, make more efficient ?

use stringbuilder rather string:

string b64stock; // <- long 1 int b = 0; stringbuilder sb = new stringbuilder(b64stock.length); foreach (char c in b64stock) {     int asciichar = (int)c;     if ((b % 2) == 0)     {         asciichar += 5;     }     else     {         asciichar -= 5;     }     sb.append((char)asciichar);     b++; } string b64readable = sb.tostring();

the performance problem you're experiencing because strings immutable. when write mystring += 'x', doesn't modify mystring. rather, creates new string of required length , copies old mystring it. kills performance relatively short strings.

the stringbuilder works expected string to. calling append adds character buffer, , buffer expanded automatically needed. although in case it's not expanded @ because pre-allocated required length.


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