Sure, can't quite work out the logic used to arrive at the number indicated (2147483647 - 0x7FFFFFFF - max value for signed int)
But I can tell you that atoi is designed to work on 32bit ints.
I think the function you're looking for is likely to be: _atoi64
char TotalSpace = "1000202039296";
printf( "[%s]\n", TotalSpace );
printf( "[%llu]\n", _atoi64( TotalSpace ) );