std::atoll with VC++

Question

I have been using std::atoll from cstdlib to convert a string to an int64_t with gcc. That function does not seem to be available on the Windows toolchain (using Visual Studio Express 2010). What is the best alternative?

I am also interested in converting strings to uint64_t. Integer definitions taken from cstdint.

Bombe

it seems this problem is fixed in VS2013 connect.microsoft.com/VisualStudio/feedback/details/752386/… – Sweatshop

Answer 1

MSVC have _atoi64 and similar functions, see here

For unsigned 64 bit types, see _strtoui64

Chaqueta

For anyone else, as a reference, this doesn't seem to have an equivalent for uint64_t, I switched to working with int64_t (casting it from a 3rd party library) – Bombe

@Cookie, added link to similar functions for unsigned 64 bit types – Chaqueta

Answer 2

• use stringstreams (<sstream>)

  std::string numStr = "12344444423223";
  std::istringstream iss(numStr);
  long long num;
  iss>>num;
  

• use boost lexical_cast (boost/lexical_cast.hpp)

   std::string numStr = "12344444423223";
   long long num = boost::lexical_cast<long long>(numStr);
  

Maeve

@Cookie: You have run a performance test and found that converting a string to a number is your bottleneck? – Maeve

valgrind is telling me that e.g. strtod is 8% of total time. atol is a bit behind with 4%. I am actually rewriting strtod to get rid of those 8%. stringstreams are considerably slower than atol. and lexical_cast is the slowest. Most of the time is spent parsing some 100 meg csv. – Bombe

The relative costs are not important if the absolute costs are negligible. Does your script run long and/or often enough to justify optimizations? (for learning purposes is of course okay) – Marge

It runs often overnight, and it often runs over 24 hours, if often runs on all 8 cores non-stop, and I often have to wait for it. A 20% difference in performance is very noticeable. Is this really the point here? Is it that hard to accept that I care about performance? Or would you like to dissect my whole project and approach before I am worthy of an answer? – Bombe

You do not know then whether strtod() has the same performance on VC++? std::sscanf() might be worth profiling in comparison to std::istringstream. – Hovis

Answer 3

If you have run a performance test and concluded that the conversion is your bottleneck and should be done really fast, and there's no ready function, I suggest you write your own. here's a sample that works really fast but has no error checking and deals with only positive numbers.

long long convert(const char* s)
{
    long long ret = 0;
    while(s != NULL)
    {
       ret*=10; //you can get perverted and write ret = (ret << 3) + (ret << 1) 
       ret += *s++ - '0';
    }
    return ret;
}

Maeve

Thanks Armen, I just might. It is very similar to #5831368 for doubles. – Bombe

Answer 4

Do you have strtoull available in your <cstdlib>? It's C99. And C++0x should also have stoull to work directly on strings.

Homunculus

Sadly, MSVC does not support C99. – Chaqueta

Answer 5

Visual Studio 2013 finally has std::atoll.

Gurge