C++ 中的异构容器

2022-01-07 00:00:00 containers c++ stl heterogeneous

我看到了这个漂亮的图形，它根据不同的数据要求对适合哪种 STL 容器进行分类，例如:

I saw this nice graphic which classifies which STL container would suit based on different requirements of data such as:

-- 固定尺寸与可变尺寸

-- Fixed Size Vs Variable size

-- 同类型数据与不同类型数据

-- Data of same tyme Vs different type

-- 排序与未排序的数据

-- Sorted Vs unsorted data

-- 顺序访问与随机访问

-- Sequential Vs random access

http://plasmahh.projectiwear.org/cce_clean.svg

我注意到在那个图像中，C++ STL 没有容器

I notice in that image, that C++ STL there is no container which is

  1. 可变尺寸
  2. 异构(不同类型的数据).

C++ 没有这方面的东西吗?

Doesn't C++ have something for this?

PS - 容器的不同属性可以有很多排列，而 STL 中可能没有提供许多其他排列.

PS - There can be many permutations made out the different properties of the containers and many others too might not be provided in STL.

推荐答案

一般来说，C++ 容器被设计为使用模板来保存单一类型的对象.如果你想要从一种类型派生的不同类型，你可以存储一个指针容器(我猜你也可以有一个 void* 容器......)例如std::vector.

Well generally C++ Containers are designed to hold objects of a single type using templates. If you want different types that are all derived from one type you can store a container of pointers (I guess you could also have a container of void* to anything...) e.g. std::vector<MyBaseType*>.

如果你想要完全不相关的类型，你可以存储可以安全引用那些其他类型的对象，例如 boost::any.

If you want completely unrelated types, you can store objects that can safely reference those other types, such as boost::any.

http://www.boost.org/doc/libs/1_47_0/doc/html/any.html

boost 网站上的一些例子:

Some examples off the boost site:

#include <list>
#include <boost/any.hpp>

using boost::any_cast;
typedef std::list<boost::any> many;

void append_int(many & values, int value)
{
    boost::any to_append = value;
    values.push_back(to_append);
}

void append_string(many & values, const std::string & value)
{
    values.push_back(value);
}

bool is_int(const boost::any & operand)
{
    return operand.type() == typeid(int);
}
bool is_char_ptr(const boost::any & operand)
{
    try
    {
        any_cast<const char *>(operand);
        return true;
    }
    catch(const boost::bad_any_cast &)
    {
        return false;
    }
}

boost::variant 类似，但您指定所有允许的类型，而不是允许容器中的任何类型.

boost::variant is similar, but you specify all the allowed types, rather than allowing any type in your container.

http://www.boost.org/doc/libs/1_47_0/doc/html/variant.html

std::vector< boost::variant<unsigned, std::string> > vec;
vec.push_back( 44);
vec.push_back( "str" );
vec.push_back( SomthingElse(55, 65) ); //not allowed

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