templating integer of unknown bitsize

How would I convert a binary/hexadecimal string into an integer, given that I don't know how large the string will be?

I want to what atoi/atol do, but I don't know what to开发者_运维问答 output because I don't know if the value will be 32 bits or 64 bits. Also, atoi doesn't do hexadecimal, so 101 will become 101 rather than 0x101==257.

I assume I need to use template<typename T>, but how would I create the variable to output in the function? T varname could be anything, so what makes varname a number rather than a pointer pointing to some random place?

Templates are a compile-time thing. You cannot choose a data-type at run-time. If your input values won't exceed the range of a 64-bit type, then simply use a 64-bit type.

One way (but by no means the only way) to do the conversion is as follows:

template <typename T>
T hex_to_int(const std::string &str)
{
    T x;
    std::stringstream(str) >> std::hex >> x;
    return x;
}

std::string str = "DEADBEEF";  // hex string
uint64_t x = hex_to_int<uint64_t>(str);
std::cout << x << std::endl;  // "3735928559"

you just need to define a bigInt class and then parse your string into that class; somthing like this class : https://mattmccutchen.net/bigint/

Maybe something like untested this:

int  // or int64 or whatever you decide on
hexstr2bin ( char *s ) {  // *s must be upper case
int result = 0;     // same type as the type of the function
  while ( *char ) {
    result <<= 16;
    if ( *char ) <= '9' {
      result += *char & 0xF;
    }
    else {
      result = ( *char & 0xF ) + 9;
    }
  }
  return result;
}