From: bop@gmb.dk   
      
   Peter Liedermann skrev 2012-04-29 22:09:   
   > Hello,   
   >   
   > The following resulted from a performance hotspot analysis in a   
   > larger context.  Small vector  variables are built up   
   > (typical size 6) and they are cleared by v.clear(). This happens   
   > millions of times.   
   >   
   > My free profiler "Very Sleepy", which has been of great use to me,   
   > points me to the following, which is not my code and therefore   
   > presumed to be STL-implementation. (VC++ 11, presumably Dinkum)   
   >   
   > void clear()   
   > 0.16s { // erase all   
   > 0.08s erase(begin(), end());   
   > 0.00s }   
   >   
   > Question: Why does it perform this erase as part of clear(), can I   
   > keep it from doing so and how? I see no point in erasing for a   
   > vector . As far as I remember what I have read, there   
   > should not be any erasing in this case. The (logical) length of the   
   > vector should be adjusted (constant complexity) and the old contents   
   > are left as garbage. Could I be better off using old C arrays?   
   >   
   > Any hint greatly appreciated, this is really a hotspot in my   
   > program.   
   >   
      
   If you can live with a C style array, where the size is never reset,   
   you can just avoid calling clear() on the vector. If you need it, you   
   need it.   
      
      
   Bo Persson   
      
      
      
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