CODEWITHSUNDEEP
c++c++11stlstd-pairstdtuple
Sanjeev
Sanjeev

Reputation: 125

Why I cannot use std::tie to unpack values from vector of pair in range based for loop

Can please someone explain why this compilation error.

Error: function template "std::tie" is not a type name This is working fine. tie(str1,str2) = pairval;

#include<iostream>
#include<vector>
#include<tuple>

using namespace std;

int main()
{

    vector<pair<string,string>>v ={{"Hello", "Task"}};

    pair<string, string> p = {"Hello", "Task"};

    string str1, str2;

    for(auto & pairval : v)
    {
        tie(str1,str2) = pairval;
        cout<<pairval.first<<" "<<pairval.second<<endl; //working
    }

    for(auto & [str1,str2]: v)
    {
       cout<<str1<<" "<<str2<<endl; //working
    }
    
    for(tie(str1, str2):v) // compilation error : function template "std::tie" is not a type name
    {
           cout<<str1<<" "<<str2<<endl;   
    }
    return 0;
}

Upvotes: 1

Views: 851

Answers (1)

ALX23z
ALX23z

Reputation: 4713

Checkout the range-for-loop definition:

for ( range_declaration : range_expression ) loop_statement

here range_declaration needs to be a declaration. std::tie(str1,str2) is not a declaration. Declaration is something like int x or auto&& y.

See cppreference for range-for-loop https://en.cppreference.com/w/cpp/language/range-for and https://en.cppreference.com/w/cpp/language/declarations for declarations.

Upvotes: 4

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