std::atoll with VC++

问题:

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.

回答1:

MSVC have _atoi64 and similar functions, see here

For unsigned 64 bit types, see _strtoui64

回答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);
  

回答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;
}

回答4:

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

回答5:

Visual Studio 2013 finally has std::atoll.