[英]I am trying to create a C++ map with a vector value inside a boost memory mapped file
This is the code I am using to test this:这是我用来测试的代码:
#include <iostream>
#include <boost/interprocess/managed_mapped_file.hpp>
#include <boost/container/map.hpp>
#include <boost/interprocess/managed_external_buffer.hpp>
#include <boost/interprocess/allocators/node_allocator.hpp>
#include <boost/container/vector.hpp>
namespace bi = boost::interprocess;
int main() {
bi::managed_mapped_file mmfile(bi::open_or_create, "map_iv.dat", 10000000);
typedef bi::allocator<int, bi::managed_mapped_file::segment_manager> int_allocator;
typedef boost::container::vector<int, int_allocator> MyVec;
typedef std::pair<const std::string, MyVec> MyPair;
typedef std::less<std::string> MyLess;
typedef bi::node_allocator<MyPair, bi::managed_mapped_file::segment_manager> node_allocator_t;
typedef boost::container::map<std::string, MyVec, std::less<std::string>, node_allocator_t> MyMap;
MyMap * mapptr = mmfile.find_or_construct<MyMap>("mymap")(mmfile.get_segment_manager());
(*mapptr)["Hello"].push_back(17);
long long s = mapptr->size();
std::cout << s << ' ';
std::cout << (*mapptr)["World"][0] << ' ';
return 0;
}
I get this error message in Visual Studio 2017:我在 Visual Studio 2017 中收到此错误消息:
boost_1_69_0\boost\container\vector.hpp(294): error C2512:
"boost::interprocess::allocator<int,boost::interprocess::segment_manager<CharType,MemoryAlgorithm,IndexType>>::allocator": no appropriate default constructor available
I am trying to get this to run and would be grateful for any help!我正在努力让它运行,并会感谢任何帮助!
I think the problem is that it cannot construct allocators for vectors.我认为问题在于它无法为向量构造分配器。 You could define an allocator class that has a default ctor which uses
mmfile.get_segment_manager()
(then you need to set that through some static data).您可以定义一个分配器 class ,它具有使用
mmfile.get_segment_manager()
的默认 ctor(然后您需要通过一些 static 数据进行设置)。 But a quick fix can be, instead of using the []
operator to add new value, use emplace
.但是一个快速的解决方法可以是使用
emplace
,而不是使用[]
运算符添加新值。
auto it = mapptr->emplace("Hello", mmfile.get_segment_manager()).first;
it->second.push_back(17);
Sorry, I haven't tested it.抱歉,我没有测试过。
The issue is that the vector can't be created without an allocator (basicly it needs to know which segment it should allocate within - it could be different from the segment the map is in).问题是没有分配器就无法创建向量(基本上它需要知道它应该在哪个段内分配 - 它可能与 map 所在的段不同)。 One way to get around this is creating a new type that uses
mmfile
global object in a constructor:解决此问题的一种方法是创建一个在构造函数中使用
mmfile
全局 object 的新类型:
bi::managed_mapped_file mmfile(bi::open_or_create, "map_iv.dat", 10000000);
int main() {
typedef bi::allocator<int, bi::managed_mapped_file::segment_manager> int_allocator;
struct MyVec : public boost::container::vector<int, int_allocator>{
MyVec() : boost::container::vector<int, int_allocator>{mmfile.get_segment_manager()}{};
};
//..
}
or you could call emplace
instead of push_back
as shown here .或者您可以调用
emplace
而不是push_back
,如此处所示。
Besides that, Im guessing it's a mistake to use std::string
in mapped_file - just a note though.除此之外,我猜在 mapped_file 中使用
std::string
是一个错误——不过只是一个注释。 The following is from a boost example - which has been modified to use the same data structure while also allocating the string in the segment:以下来自一个boost 示例- 它已被修改为使用相同的数据结构,同时还在段中分配字符串:
#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/containers/map.hpp>
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/containers/string.hpp>
int main ()
{
using namespace boost::interprocess;
//Typedefs of allocators and containers
typedef managed_shared_memory::segment_manager segment_manager_t;
typedef allocator<void, segment_manager_t> void_allocator;
typedef allocator<int, segment_manager_t> int_allocator;
typedef vector<int, int_allocator> int_vector;
typedef allocator<char, segment_manager_t> char_allocator;
typedef basic_string<char, std::char_traits<char>, char_allocator> char_string;
//Definition of the map holding a string as key and complex_data as mapped type
typedef std::pair<const char_string, int_vector> map_value_type;
typedef std::pair<char_string, int_vector> movable_to_map_value_type;
typedef allocator<map_value_type, segment_manager_t> map_value_type_allocator;
typedef map< char_string, int_vector, std::less<char_string>, map_value_type_allocator> complex_map_type;
shared_memory_object::remove("MySharedMemory");
remove_shared_memory_on_destroy remove_on_destroy("MySharedMemory");
{
//Create shared memory
managed_shared_memory segment(create_only,"MySharedMemory", 65536);
//An allocator convertible to any allocator<T, segment_manager_t> type
void_allocator alloc_inst (segment.get_segment_manager());
//Construct the shared memory map and fill it
complex_map_type *mymap = segment.construct<complex_map_type>
//(object name), (first ctor parameter, second ctor parameter)
("MyMap")(std::less<char_string>(), alloc_inst);
for(int i = 0; i < 100; ++i){
//Both key(string) and value(complex_data) need an allocator in their constructors
char_string key_object(alloc_inst);
int_vector mapped_object(alloc_inst);
mapped_object.push_back(i);
map_value_type value(key_object, mapped_object);
//Modify values and insert them in the map
mymap->insert(value);
}
}
return 0;
}
So this seems to work:所以这似乎有效:
#include <iostream>
#include <boost/interprocess/managed_mapped_file.hpp>
#include <boost/container/map.hpp>
#include <boost/interprocess/managed_external_buffer.hpp>
#include <boost/interprocess/allocators/node_allocator.hpp>
#include <boost/container/vector.hpp>
namespace bi = boost::interprocess;
int main() {
bi::managed_mapped_file mmfile(bi::open_or_create, "map_iv.dat", 10000000);
typedef bi::allocator<int, bi::managed_mapped_file::segment_manager> int_allocator;
typedef boost::container::vector<int, int_allocator> MyVec;
typedef std::pair<const std::string, MyVec> MyPair;
typedef std::less<std::string> MyLess;
typedef bi::node_allocator<MyPair, bi::managed_mapped_file::segment_manager> node_allocator_t;
typedef boost::container::map<std::string, MyVec, std::less<std::string>, node_allocator_t> MyMap;
MyMap * mapptr = mmfile.find_or_construct<MyMap>("mymap")(mmfile.get_segment_manager());
MyVec * vecptr = mmfile.find_or_construct<MyVec>("myvector")(mmfile.get_segment_manager());
mapptr->emplace(std::string("Hello"), *vecptr);
//(*mapptr)["Hello"] = *vecptr;
(*vecptr).push_back(17);
long long s = mapptr->size();
std::cout << s << ' ';
std::cout << (*mapptr).at("Hello")[0] << ' ';
for (auto& i : *mapptr)
std::cout << i.first << ':' << i.second[0] << ' ';
return 0;
}
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