如何在C ++中构建和使用vector（map（pair（struct）））？

Question

I want to build a variable like vector(map(pair(struct))) and use it to store information in C++, I try to use following code:

struct st_Base
{
    char Type[2];
    double Price;
    queue<double> Samples;
};

vector< map< string, pair< st_Base, st_Base >* >* > gv_combo;

string str_source = "test123";

gv_combo.push_back(new map<str_source, new pair<st_Base, st_Base>>);

But when I run the program, it always show me lots of errors. Can anyone told me the right way to build it, place data in it, and read it?

Answer 1

Consider not using dynamic allocation via new keyword (Manual memory management is prone to errors). If your memory needs to be allocated dynamically use unique pointer std::unique_ptr .

What you are esentially creating is a container holding a pointer to container that is holding a pair of values (string (key), and pointer to pair of structs (value)).

#include <vector>
#include <map>
#include <utility>
#include <memory>
#include <iostream>



struct st_Base { int foo; };

int main()
{
    typedef std::pair< st_Base, st_Base> weird_pair;
    std::vector<std::map<std::string, weird_pair>> gv_combo;

    string str_source = "test123";
    weird_pair pair = make_pair(st_Base{ 10 }, st_Base{ 11 });
    gv_combo.push_back(std::map<std::string, weird_pair>()); 

    gv_combo.at(0).insert(std::pair<std::string, weird_pair>(str_source, pair));

    std::cout << gv_combo.at(0).at("test123").second.foo;

    return 1;

}

But this example is extremly unreadable (at least for me). Access to members of structs is not straightforwarwd (needs to call at() to localize element in map, then use first/second to access apropriate st_Base which results in ever increasing chain of calls. Adding unique_ptr would result in even longer chain that would put my brain on a verge of scrapping the entire code after working with it for any period of time.

Notes to OP:
-read documentation carefully, it's your friend
-allocate with keyword new only when you really have to (eg. obscure framework pre c++11)
-typedefs save lifes
-pointers can get out of hand quickly if you don't wrap them into nice structure
-objects can use initializer lists {} to give them data during construction of the object. it's worth noting that C and C++ versions {} are not exchangable ( st_Base{.foo=10} is legal in C, but illegal in c++ )

Answer 2

This seems to be what you are trying to achieve:

struct st_Base {
    char Type[2];
    double Price;
    std::queue<double> Samples;
};

std::vector<std::map<std::string, std::pair<st_Base, st_Base>>> gv_combo;

string str_source = "test123";
std::map<std::string, std::pair<st_Base, st_Base>> my_map;
my_map[str_source] = std::make_pair(st_Base(...), st_Base(...)); // instert pair of objects here

gv_combo.push_back(my_map);