Convert an ASCII string to long long

I've got some line开发者_StackOverflow社区s of information from a data-file in C++. One information is a 12 character long number. How can I convert this from string to long long (I think long long is most suitable for this) without data loss?

In C++, there is no long long data type. It's available in C99. However, you can use int64_t. Include <stdint.h>.

Use boost::lexical_cast to convert string into int64_t.

Or you can write a convert function yourself as:

int64_t convert(const std::string &s)
{
   if(s.size() == 0 ) 
       std::runtime_error error("invalid argument");
   int64_t v = 0;
   size_t i=0;
   char sign = (s[0] == '-' || s[0] == '+') ? (++i, s[0]) : '+';
   for( ; i < s.size(); ++i)
   {
      if ( s[i] < '0' || s[i] > '9' )
          throw std::runtime_error("invalid argument");
      v = v * 10 + s[i] - '0';
   }
   return sign == '-' ? -v : v;
}

Test code:

int main() {
        try{
           std::cout << convert("68768768") << std::endl;
           std::cout << convert("+68768768") << std::endl;
           std::cout << convert("-68768768") << std::endl;
           std::cout << convert("68768768x") << std::endl;
        }catch(const std::exception &e)
        {
           std::cout << e.what() << std::endl;
        }
        return 0;
}

Output:

68768768
68768768
-68768768
invalid argument

Online demo : http://ideone.com/nnSLp

A 64-bit bit integer is enough to represent any 12-digit decimal number (with plenty of room to spare). Thus, depending on your platform, it could be that a long will suffice. If that's the case, you could use strtol or strtoul.

If you do find that you need a long long, take a look at strtoll and strtoull.