Question

I need to read exactly 32 bits from a file. I’m using ifstream in the STL. Can I just directly say:

int32 my_int;
std::ifstream my_stream;

my_stream.open("my_file.txt",std::ifstream::in);
if (my_stream && !my_stream.eof())
   my_stream >> my_int;

…or do I need to somehow override the >> operator to work with int32? I don’t see the int32 listed here:
http://www.cplusplus.com/reference/iostream/istream/operator%3E%3E/

Answer 1

The stream extraction operator (>>) performs formatted IO, not binary IO. You’ll need to use std::istream::read instead. You’ll also need to open the file as binary. Oh, and checking std::istream::eof is redundant in your code.

int32 my_int;
std::ifstream my_stream;

my_stream.open("my_file.txt",std::ios::in | std::ios::binary);
if (my_stream)
{
    my_stream.read(reinterpret_cast<char*>(&my_int), sizeof(my_int));
}
//Be sure to check my_stream to see if the read succeeded.

Note that doing this is going to introduce platform dependence on your code, because the order of bytes in an integer is different on different platforms.