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- // endian_example.cpp -------------------------------------------------------//
- // Copyright Beman Dawes, 2006
- // Distributed under the Boost Software License, Version 1.0.
- // See http://www.boost.org/LICENSE_1_0.txt
- // See library home page at http://www.boost.org/libs/endian
- //----------------------------------------------------------------------------//
- #include <boost/endian/detail/disable_warnings.hpp>
- #include <iostream>
- #include <cstdio>
- #include <boost/endian/buffers.hpp>
- #include <boost/static_assert.hpp>
- using namespace boost::endian;
- namespace
- {
- // This is an extract from a very widely used GIS file format. Why the designer
- // decided to mix big and little endians in the same file is not known. But
- // this is a real-world format and users wishing to write low level code
- // manipulating these files have to deal with the mixed endianness.
- struct header
- {
- big_int32_buf_at file_code;
- big_int32_buf_at file_length;
- little_int32_buf_at version;
- little_int32_buf_at shape_type;
- };
- const char* filename = "test.dat";
- }
- int main(int, char* [])
- {
- header h;
- BOOST_STATIC_ASSERT(sizeof(h) == 16U); // reality check
- h.file_code = 0x01020304;
- h.file_length = sizeof(header);
- h.version = 1;
- h.shape_type = 0x01020304;
- // Low-level I/O such as POSIX read/write or <cstdio> fread/fwrite is sometimes
- // used for binary file operations when ultimate efficiency is important.
- // Such I/O is often performed in some C++ wrapper class, but to drive home the
- // point that endian integers are often used in fairly low-level code that
- // does bulk I/O operations, <cstdio> fopen/fwrite is used for I/O in this example.
- std::FILE* fi = std::fopen(filename, "wb"); // MUST BE BINARY
- if (!fi)
- {
- std::cout << "could not open " << filename << '\n';
- return 1;
- }
- if (std::fwrite(&h, sizeof(header), 1, fi)!= 1)
- {
- std::cout << "write failure for " << filename << '\n';
- return 1;
- }
- std::fclose(fi);
- std::cout << "created file " << filename << '\n';
- return 0;
- }
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