Question

Simple question; what’s better and why?

      out.resize( in.size() );     T1::iterator outit = out.begin();     for( inIt = in.begin() to end, ++inIt, ++outIt )        *outit = *inIt OR      out.erase();     for( inIt = in.begin() to end, ++inIt )         out.push_back( inIt );   

I’m assuming the memory assignment implicit in push_back is worth avoiding but want to make sure.

Thanks

EDIT: Thanks for the out = in suggestions guys ;). The actual code I’m playing with is:

 template//can't stop the browser ignoring th class T1, class T2 in angle brackets bool asciihex( T1& out, const T2& in ) {     //out.erase();     out.resize( in.size() / 2 );     if( std::distance( in.begin(), in.end() ) % 2 )//use distance rather than size to minimise the requirements on T2?         return false;     for( T2::const_iterator it = in.begin(); it != in.end(); it += 2 )     {         out.push_back(((( (*it > '9' ? *it - 0x07 : *it)  - 0x30)  '9' ? *(it+1) - 0x07 : *(it+1)) - 0x30) & 0x000f));     }     return true; }  template bool asciihex( T1& out, const T2& in ) {     size_t size = in.size();     if( size % 2 )//use distance rather than size to minimise the requirements on T2?         return false;     out.resize( size / 2 );     T1::iterator outit = out.begin();     for( T2::const_iterator it = in.begin(); it != in.end(); it += 2, ++outit )     {         *outit = ((( (*it > '9' ? *it - 0x07 : *it)  - 0x30)  '9' ? *(it+1) - 0x07 : *(it+1)) - 0x30) & 0x000f);     }     return true; } 

Edit: I’ve marked push_back as the answer as it seems to be the consensus and, therefore, more useful to anyone else with the same problem. However I have ended up using the iterator method as one of the container classes I’m interested in doesn’t support push_back… mileage varies.

Answer 1

The second, and if you’re concerned about multiple extensions use out.reserve(). The right answer to adding to a vector is almost always push_back or back_inserter, which avoid some possible problems (exception guarantees, constructors, writing past the end, for example) that you’d have to pay attention to with other methods.