I need to use a 128 bit unsigned int variable in my code.
Searching on line I read about unsigned __int128.
Here https://gcc.gnu.org/onlinedocs/gcc/_005f_005fint128.html I read
type __int128 is supported for targets which have an integer mode wide enough to hold 128 bits
My first question is what does it means with target? what I have to check to see if my pc can express such type?
The second question is how to print such kind of variable?
Lastly do I need to do something to use this kind of variables? The same above link says
Simply write __int128 for a signed 128-bit integer, or unsigned __int128 for an unsigned 128-bit integer.
So it seems I don't need to #include anything and I even don't add some option in gcc during the compiolation, is it right?
"Target" means the specific combination of CPU architecture and operating system that your compiler is configured to create programs for. There is a discussion at Does a list of all known target triplets in use exist?. But "integer mode" is really a concept used internally by the compiler, and only indirectly related to what the hardware can and can't do. So all this really says is "the compiler supports 128-bit integers on some targets and not on others". The easiest way to find out whether yours does is to just try to compile and run a small test program that uses __int128.
Most system's printf functions don't support __int128, so you have to write your own code to print them, or find third-party code somewhere. See How to print __int128 in g++? which is for C++ but still relevant.
You don't need to include anything or use any special options.