boost exception

boost exception provides a new exception type,that lets you add data to an exception after it has been thrown.

#include <boost/exception/all.hpp>
#include <exception>
#include <@H_675_12@new>
#include <@H_675_12@String>
#include <algorithm>
#include <limits>
#include <iostream>

typedef boost::error_info<@H_675_12@struct tag_errmsg,std::@H_675_12@String> errmsg_info;

@H_675_12@struct alLOCATIOn_Failed : @H_675_12@public boost::exception,@H_675_12@public std::exception
{
  @H_675_12@const @H_675_12@char *what() @H_675_12@const noexcept { @H_675_12@return "alLOCATIOn Failed"; }
};

@H_675_12@char *allocate_memory(std::size_t sizE)
{
  @H_675_12@char *c = @H_675_12@new (std::nothrow) @H_675_12@char[size];
  @H_675_12@if (!C)
    @H_675_12@throw alLOCATIOn_Failed{};
  @H_675_12@return c;
}

@H_675_12@char *write_lots_of_zeros()
{
  @H_675_12@try
  {
    @H_675_12@char *c = allocate_memory(std::numeric_limits<std::size_t>::max());
    std::fill_n(c,std::numeric_limits<std::size_t>::max(),0);
    @H_675_12@return c;
  }
  @H_675_12@catch (boost::exception &E)
  {
    e << errmsg_info{"wriTing lots of zeros Failed"};
    @H_675_12@throw;
  }
}

@H_675_12@int main()
{
  @H_675_12@try
  {
    @H_675_12@char *c = write_lots_of_zeros();
    @H_675_12@delete[] c;
  }
  @H_675_12@catch (boost::exception &E)
  {
    std::cerr << boost::diagnostic_information(E);
  }
  @H_675_12@return 0;
}

output:

Throw LOCATIOn unkNown (consider using BOOST_THROW_EXCEPTION) Dynamic exception type: struct alLOCATIOn_Failed std::exception::what: alLOCATIOn Failed [struct tag_errmsg *] = wriTing lots of zeros Failed

unction write_lots_of_zeros() calls allocate_memory(). allocate_memory() allocates memory dynamically. The function passes std::nothrow to new and checks whether the return values is 0. if memory alLOCATIOn fails,an exception of type alLOCATIOn_Failed is thrown.

write_lots_of_zeros() calls allocate_memory() to try and allocate a memory block with the greatest possible size. This is done with the Help of @H_684_167@max() from std::numeric_limits. The examplE intentionally tries to allocate that much memory to make the alLOCATIOn fail.

With Boost.Exception,data can be added to an exception at any time. You just need to define a type based on boost::error_info for each bit of data you need to add.

boost::error_info is a template that expects two parameters. The first parameter is a atag that uniquely identifies the newly created type. This is typically a structure with a unique name. The second parameter refers to the type of the value stored inside the exception.

In the catch handler of write_lots_of_zeros(),errmsg_info is used to create an object that is initialized with the String “wriTing lots of zeros Failed”. This object is then added to the exception of type boost::exception using operator<<. Then the exception is re-thrown.

2. BOOST_THROW_EXCEPTION

@H_675_12@char *allocate_memory(std::size_t sizE)
{
  @H_675_12@char *c = @H_675_12@new (std::nothrow) @H_675_12@char[size];
  @H_675_12@if (!C)
    BOOST_THROW_EXCEPTION(alLOCATIOn_Failed{});
  @H_675_12@return c;
}

output:

using the macro BOOST_THROW_EXCEPTION instead of throw,data such as function name,file name,and line number are automatically added to the exception.

BOOST_THROW_EXCEPTION accesses the function boost::enable_error_info(),which identifies whether or not an exception is derived from boost::exception. If not,it creates a new exception type derived from the specified type and boost::exception.