Very poor boost::lexical_cast performance

Question

Windows XP SP3. Core 2 Duo 2.0 GHz. I\'m finding the boost::lexical_cast performance to be extremely slow. Wanted to find out ways to speed up the code. Using /O2 optimizati

Answer 1

What lexical cast is doing in your code can be simplified to this:

string Cast( int i ) {
    ostringstream os;
    os << i;
    return os.str();
}

There is unfortunately a lot going on every time you call Cast():

• a string stream is created possibly allocating memory
• operator << for integer i is called
• the result is stored in the stream, possibly allocating memory
• a string copy is taken from the stream
• a copy of the string is (possibly) created to be returned.
• memory is deallocated

Thn in your own code:

 s = Cast( i );

the assignment involves further allocations and deallocations are performed. You may be able to reduce this slightly by using:

string s = Cast( i );

instead.

However, if performance is really importanrt to you, you should considerv using a different mechanism. You could write your own version of Cast() which (for example) creates a static stringstream. Such a version would not be thread safe, but that might not matter for your specific needs.

To summarise, lexical_cast is a convenient and useful feature, but such convenience comes (as it always must) with trade-offs in other areas.