Inserting a struct as a value in Multimap and Iterating the same to get the values

Question

#include <stdio.h>
#include <map>
struct temp
{
   int x;
   int id;
};

int main()
{
    temp t;
    int key;
    typedef std::multimap<int,struct temp> mapobj;
    t.x = 10;
    t.id = 20;
    key=1;
    mapobj.insert(pair<int,struct>key,t);
    //mapobj.insert(1,t);
    
    return 0;
 }

I am new to STL multimap, I'm trying to insert my structure data inside the multimap but I get this error:

main.cpp:25:11: error: expected unqualified-id before ‘.’ token
     mapobj.insert(pair<int,struct temp>key,t);
           ^

seeking your suggestion on this.

`typedef` declares a type alias, not a variable of the given type. — chi, Jul 03 '21 at 15:37
Also note the typo(s) in `mapobj.insert(pairkey,t);` and that you don't need the `struct` keyword when referring to a type. — Lukas-T, Jul 03 '21 at 15:44
Welcome to Stack Overflow. Did you master `multimap` before attempting this? — Beta, Jul 03 '21 at 15:48
if i remove the alias "typedef" then i get the below error, main.cpp:25:19: error: ‘pair’ was not declared in this scope mapobj.insert(pairkey,t); ^~~~ — Ganesh Sha, Jul 03 '21 at 16:11

Job_September_2020 · Accepted Answer · 2021-07-03T17:24:59.407

I think you need to make some minor code changes to fix the compile error as follows:

Add 2 brackets: mapobj.insert(std::pair<int,struct temp> (key,t) );
Add "struct temp" in mapobj.insert(std::pair<int,struct temp>(key,t)); (Note: You did not have the name of the struct: temp).
Please note that you should specify std::pair the second times you use mapobj at the bottom of your file.
Remove the keyword Tydef (as user "Sam Varshavchik" mentioned because you don't need to define a new type and you only need to define a new variable).
BTW, the following issue does not cause the compile error, but it will be a good thing if you initialize the value of "key" because if you do not initialize the value for "key", then key may have random values that is not zero. This is called undefined behavior, and it may cause some bug later on.

Here is the new code that compiles successfully:

#include <stdio.h>
#include <map>
    
struct temp
{
   int x;
   int id;
};

int main()
{
    temp t;
    int key = 1; // You should initialize the key
    std::multimap<int,struct temp> mapobj; // I fixed this line
    t.x = 10;
    t.id = 20;
    key=1;
    mapobj.insert(std::pair<int,struct temp>(key,t)); // I fixed this line
    //mapobj.insert(1,t);
    
    return 0;
 }

I still see this error on compiling of the changed code as well, 20 | mapobj.insert(pair(key,t)); // I fixed this line | ^~~~ | std::pair — Ganesh Sha, Jul 03 '21 at 17:12
@Ganesh Sha, To fix that, we need to fully specify "std::pair" in "mapobj.insert(std::pair(key,t));" - I have just fixed that in the code, and it should compile now. Please try again and let me know. — Job_September_2020, Jul 03 '21 at 17:18

Inserting a struct as a value in Multimap and Iterating the same to get the values

1 Answers1