I am new to C . I found that to see a variable's type, I can use typeid().name() on library "typeinfo". But when I implement this function on map data structure, I got this output

Type of itr is : St17_Rb_tree_iteratorISt4pairIKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEiEE

What is that mean ? Actually I want to know what is type of itr which is the iterator of map in the code section.

#include <iostream>
#include <string>
#include <iterator>
#include <map>
#include <typeinfo>

using namespace std;
    
int main()
{

    map <string, int> map1;

    map1.insert({"A",1});

    auto itr = map1.begin();        // Iterator is created by auto

    for (itr; itr != map1.end(); itr  )
    {
        cout<<itr->first<<"  "<<itr->second<<"\n";
    }

    cout<<"Type of itr is : "<<typeid(itr).name();
    
    return 0;
}

CodePudding user response：

I want to know what is type of itr which is the iterator of map in the code section?

The type of map1.begin() is

std::map<std::string, int>::iterator

You can test it via

#include <type_traits> // std::is_same_v

static_assert(std::is_same_v<
     decltype(map1.begin()), std::map<std::string, int>::iterator>
    , "are not same");

i.e. Alternative to auto keyword and the above (i.e std::map<std::string, int>::iterator), you could use decltype(map1.begin()) as well.

St17_Rb_tree_iteratorISt4pairIKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEiEE

What is that mean ?

It's the name of the type as per compiler implementations. From std::type_info::name

Returns an implementation defined null-terminated character string containing the name of the type. No guarantees are given; in particular, the returned string can be identical for several types and change between invocations of the same program.

Therefore, it could vary compiler-to-compiler, and can not argue this will look the same always. For instance, have a look into the type of map1.begin() in different compiler here: https://gcc.godbolt.org/z/ProxxaxfW

CodePudding user response：

#include <iostream>
#include <string>
#include <iterator>
#include <map>
#include <typeinfo>

using namespace std;
    
int main()
{

    map <string, int> map1;

    map1.insert({"A",1});

    auto itr = map1.begin();        // Iterator is created by auto

    for (itr; itr != map1.end(); itr  )
    {
        cout<<itr->first<<"  "<<itr->second<<"\n";
    }

    cout<<"Type of itr is : "<<typeid(itr).name();
    
    return 0;
}