+++ /dev/null
-// Copyright (c) 2018-2020 Emil Dotchevski and Reverge Studios, Inc.
-
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-
-// This is the program presented in https://boostorg.github.io/leaf/#introduction-result,
-// converted to use outcome::result instead of leaf::result.
-
-// It reads a text file in a buffer and prints it to std::cout, using LEAF to handle errors.
-// This version does not use exception handling.
-
-#include <boost/outcome/std_result.hpp>
-#include <boost/leaf/handle_errors.hpp>
-#include <boost/leaf/pred.hpp>
-#include <boost/leaf/on_error.hpp>
-#include <boost/leaf/common.hpp>
-#include <iostream>
-#include <memory>
-#include <stdio.h>
-
-namespace outcome = boost::outcome_v2;
-namespace leaf = boost::leaf;
-
-
-// First, we need an enum to define our error codes:
-enum error_code
-{
- bad_command_line = 1,
- open_error,
- read_error,
- size_error,
- eof_error,
- output_error
-};
-
-
-template <class T>
-using result = outcome::std_result<T>;
-
-// To enable LEAF to work with outcome::result, we need to specialize the is_result_type template:
-namespace boost { namespace leaf {
- template <class T> struct is_result_type<outcome::std_result<T>>: std::true_type { };
-} }
-
-
-// We will handle all failures in our main function, but first, here are the declarations of the functions it calls, each
-// communicating failures using result<T>:
-
-// Parse the command line, return the file name.
-result<char const *> parse_command_line( int argc, char const * argv[] );
-
-// Open a file for reading.
-result<std::shared_ptr<FILE>> file_open( char const * file_name );
-
-// Return the size of the file.
-result<int> file_size( FILE & f );
-
-// Read size bytes from f into buf.
-result<void> file_read( FILE & f, void * buf, int size );
-
-
-// The main function, which handles all errors.
-int main( int argc, char const * argv[] )
-{
- return leaf::try_handle_all(
-
- [&]() -> result<int>
- {
- BOOST_LEAF_AUTO(file_name, parse_command_line(argc,argv));
-
- auto load = leaf::on_error( leaf::e_file_name{file_name} );
-
- BOOST_LEAF_AUTO(f, file_open(file_name));
-
- BOOST_LEAF_AUTO(s, file_size(*f));
-
- std::string buffer(1 + s, '\0');
- BOOST_LEAF_CHECK(file_read(*f, &buffer[0], buffer.size()-1));
-
- std::cout << buffer;
- std::cout.flush();
- if( std::cout.fail() )
- return leaf::new_error(output_error, leaf::e_errno{errno}).to_error_code();
-
- return 0;
- },
-
- // Each of the lambdas below is an error handler. LEAF will consider them, in order, and call the first one that matches
- // the available error objects.
-
- // This handler will be called if the error includes:
- // - an object of type error_code equal to open_error, and
- // - an object of type leaf::e_errno that has .value equal to ENOENT, and
- // - an object of type leaf::e_file_name.
- []( leaf::match<error_code, open_error>, leaf::match_value<leaf::e_errno, ENOENT>, leaf::e_file_name const & fn )
- {
- std::cerr << "File not found: " << fn.value << std::endl;
- return 1;
- },
-
- // This handler will be called if the error includes:
- // - an object of type error_code equal to open_error, and
- // - an object of type leaf::e_errno (regardless of its .value), and
- // - an object of type leaf::e_file_name.
- []( leaf::match<error_code, open_error>, leaf::e_errno const & errn, leaf::e_file_name const & fn )
- {
- std::cerr << "Failed to open " << fn.value << ", errno=" << errn << std::endl;
- return 2;
- },
-
- // This handler will be called if the error includes:
- // - an object of type error_code equal to any of size_error, read_error, eof_error, and
- // - an optional object of type leaf::e_errno (regardless of its .value), and
- // - an object of type leaf::e_file_name.
- []( leaf::match<error_code, size_error, read_error, eof_error>, leaf::e_errno const * errn, leaf::e_file_name const & fn )
- {
- std::cerr << "Failed to access " << fn.value;
- if( errn )
- std::cerr << ", errno=" << *errn;
- std::cerr << std::endl;
- return 3;
- },
-
- // This handler will be called if the error includes:
- // - an object of type error_code equal to output_error, and
- // - an object of type leaf::e_errno (regardless of its .value),
- []( leaf::match<error_code, output_error>, leaf::e_errno const & errn )
- {
- std::cerr << "Output error, errno=" << errn << std::endl;
- return 4;
- },
-
- // This handler will be called if we've got a bad_command_line
- []( leaf::match<error_code, bad_command_line> )
- {
- std::cout << "Bad command line argument" << std::endl;
- return 5;
- },
-
- // This last handler matches any error: it prints diagnostic information to help debug logic errors in the program, since it
- // failed to match an appropriate error handler to the error condition it encountered. In this program this handler will
- // never be called.
- []( leaf::error_info const & unmatched )
- {
- std::cerr <<
- "Unknown failure detected" << std::endl <<
- "Cryptic diagnostic information follows" << std::endl <<
- unmatched;
- return 6;
- } );
-}
-
-
-// Implementations of the functions called by main:
-
-
-// Parse the command line, return the file name.
-result<char const *> parse_command_line( int argc, char const * argv[] )
-{
- if( argc==2 )
- return argv[1];
- else
- return leaf::new_error(bad_command_line).to_error_code();
-}
-
-
-// Open a file for reading.
-result<std::shared_ptr<FILE>> file_open( char const * file_name )
-{
- if( FILE * f = fopen(file_name, "rb") )
- return std::shared_ptr<FILE>(f, &fclose);
- else
- return leaf::new_error(open_error, leaf::e_errno{errno}).to_error_code();
-}
-
-
-// Return the size of the file.
-result<int> file_size( FILE & f )
-{
- auto load = leaf::on_error([] { return leaf::e_errno{errno}; });
-
- if( fseek(&f, 0, SEEK_END) )
- return leaf::new_error(size_error).to_error_code();
-
- int s = ftell(&f);
- if( s==-1L )
- return leaf::new_error(size_error).to_error_code();
-
- if( fseek(&f,0,SEEK_SET) )
- return leaf::new_error(size_error).to_error_code();
-
- return s;
-}
-
-
-// Read size bytes from f into buf.
-result<void> file_read( FILE & f, void * buf, int size )
-{
- int n = fread(buf, 1, size, &f);
-
- if( ferror(&f) )
- return leaf::new_error(read_error, leaf::e_errno{errno}).to_error_code();
-
- if( n!=size )
- return leaf::new_error(eof_error).to_error_code();
-
- return outcome::success();
-}
-
-////////////////////////////////////////
-
-#ifdef BOOST_LEAF_NO_EXCEPTIONS
-
-namespace boost
-{
- BOOST_LEAF_NORETURN void throw_exception( std::exception const & e )
- {
- std::cerr << "Terminating due to a C++ exception under BOOST_LEAF_NO_EXCEPTIONS: " << e.what();
- std::terminate();
- }
-
- struct source_location;
- BOOST_LEAF_NORETURN void throw_exception( std::exception const & e, boost::source_location const & )
- {
- throw_exception(e);
- }
-}
-
-#endif
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