c++ - Performance tuning -

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i have following code segment . vector of size 176000 loop takes upto 8 minutes execute . not sure taking time 

    xepcombstr bstrsetwithidsasstring; //wrapper class bstr     std::vector<__int64>::const_iterator it;     for(it = vecids.begin();         != vecids.end();         it++)     {                     __int64 i64id = (*it);                   __int64 i64oid = xptfunctions::getoid(i64id);                      // set ',' between 2 set members                   if (it != vecids.begin())                         bstrsetwithidsasstring.append(xepcombstr(l","));                       wchar_t buf[20];         _i64tow_s(i64oid, buf, 20, 10);         bstrsetwithidsasstring.append(buf);     }   __int64 getoid( const __int64 &i64id) {     __int64 numid = i64id;     numid <<= 16;     numid >>= 16;     return numid; }

i think bottleneck append function. see, string has allocated memory inside, , when try append won't fit, reallocates more memory, takes lot of time. try allocating necessary memory once in beginning. hth


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