Question

Recently, I try to use the boost::spirit::qi binary endian parser to parse some binary data depends on the endianness of the Platform. There is a simple example, like following:

Using declarations and variables:

using boost::spirit::qi::little_word;
using boost::spirit::qi::little_dword;
using boost::spirit::qi::little_qword;

boost::uint16_t us;
boost::uint32_t ui;
boost::uint64_t ul;

Basic usage of the little endian binary parsers:

test_parser_attr("\x01\x02", little_word, us); assert(us == 0x0201);
test_parser_attr("\x01\x02\x03\x04", little_dword, ui); assert(ui == 0x04030201);
test_parser_attr("\x01\x02\x03\x04\x05\x06\x07\x08", little_qword, ul);
assert(ul == 0x0807060504030201LL);

test_parser("\x01\x02", little_word(0x0201));
test_parser("\x01\x02\x03\x04", little_dword(0x04030201));
test_parser("\x01\x02\x03\x04\x05\x06\x07\x08",
    little_qword(0x0807060504030201LL));

It works very well. But my questions come, why do we need use some data types like boost::uint16_t, boost::uint32_t here? Can I use unsigned long or unsigned int here?
And if I want to parse double or float data type, what boost data type should I use? And please tell me where is boost define the above these types?

Answer 1

Types like uint16_t or uint32_t exist so that you can declare a variable to have a specific bit width. You can’t do this with normal types like “long” because they are different sizes on different architectures and/or implementations. The afore mentioned types are normally derived by through preprocessor calculations resulting in typedefs to the implementation/architectural specific type to get that specific size.