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 optimizations on visual c++ 2008 and comparing with java 1.6 and python 2.6.2 I see the following results.
Integer casting:
c++:
std::string s ;
for(int i = 0; i < 10000000; ++i)
{
s = boost::lexical_cast<string>(i);
}
java:
String s = new String();
for(int i = 0; i < 10000000; ++i)
{
s = new Integer(i).toString();
}
python:
for i in xrange(1,10000000):
s = str(i)
The times I'm seeing are
c++: 6700 milliseconds
java: 1178 milliseconds
python: 6702 milliseconds
c++ is as slow as python and 6 times slower than java.
Double casting:
c++:
std::string s ;
for(int i = 0; i < 10000000; ++i)
{
s = boost::lexical_cast<string>(d);
}
java:
String s = new String();
for(int i = 0; i < 10000000; ++i)
{
double d = i*1.0;
s = new Double(d).toString();
}
python:
for i in xrange(1,10000000):
d = i*1.0
s = str(d)
The times I'm seeing are
c++: 56129 milliseconds
java: 2852 milliseconds
python: 30780 milliseconds
So for doubles c++ is actually half the speed of python and 20 times slower than the java solution!!. Any ideas on improving the boost::lexical_cast performance? Does this stem from the poor stringstream implementation or can we expect a general 10x decrease in performance from using the boost libraries.
You could specialize
lexical_cast
forint
anddouble
types. Usestrtod
andstrtol
in your's specializations.This variant will be faster than using default implementation, because in default implementation there is construction of heavy stream objects. And it is should be little faster than
printf
, becauseprintf
should parse format string.I use this very fast solution for POD types...
As Barry said,
lexical_cast
is very general, you should use a more specific alternative, for example check out itoa (int->string
) and atoi (string -> int
).