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;
}
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
我正在尝试让它运行,如果有任何帮助,我将不胜感激!
最佳答案
问题是如果没有分配器就无法创建 vector (基本上它需要知道应该在哪个段中分配 - 它可能与 map 所在的段不同)。解决这个问题的一种方法是创建一个在构造函数中使用 mmfile
全局对象的新类型:
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()}{};
};
//..
}
或者您可以调用 emplace
而不是 push_back
,如下所示 here .
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。以下内容来自boost example - 已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;
}
关于c++ - 我正在尝试创建一个 C++ 映射,其中包含 boost 内存映射文件中的 vector 值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58647252/