std::atoll with VC++ | 易学教程

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;
}