Is there any way to append initializer list --> std::initializer_list<std::pair<std::string, std::string>>?

Rishabh Madan 0
Viewed 46

In my project there is need to append initializer list at runtime.

I have figured the way to have initializer_list std::initializer_list<std::pair<std::string, std::string>> at runtime in my project, but not able to figure out way to append this list if user passing multiple no. of pairs.

dummy code implementation of that part is below:

#include <iostream>
#include <string.h>
#include <initializer_list>


#define __FILENAME__ strrchr(__FILE__, '/') ? strrchr(__FILE__, '/') + 1 : __FILE__
#define S1(x) #x
#define S2(x) S1(x)
#define LOCATION std::string(__FILENAME__) + ":" + std::string(S2(__LINE__)) + ":" + std::string(__PRETTY_FUNCTION__)
#define ATTR_PAIR std::pair<std::string, std::string>("Log.Details",LOCATION)

int main()
{
    std::string s = "op";
    std::string s1 = "de";
    std::string s2 = "en";

    auto pa = std::make_pair(s,s1);
    auto pb = std::make_pair(s,s2);

    auto list = {pb,pa};

    std::initializer_list<std::pair<std::string, std::string>> L({list}) ;
    
    std::initializer_list<std::pair<std::string, std::string>> I = {ATTR_PAIR,*(L .begin()),*(L.begin()+1)};   //is there any generic way to append this with as much pairs user passes in list

    for(auto it=I.begin();it!=I.end();++it)
    {
        std::cout<<(it->first)<<std::endl;
        std::cout<<(it->second)<<std::endl;
    }   
}

my need is to append initializer I with as much pair I have in list . code which I wrote here, I have passed (L.begin()+1) to have 2nd pair. Is there any other generic way to do so???

append list-initialization initializer-list c++
1 Answers

The length of a std::initializer_list cannot be chosen dynamically at runtime and list's length here is not a compile-time usable property.

std::initializer_list is the wrong tool for this. It should only be used as parameters to functions or implicitly in e.g. a range-for loop. In any case only directly to store a {/*...*/} braced-initializer-list temporarily to be processed further e.g. into a proper container to copy elements from.

If you need a sequence container with runtime-determined dimensions, use std::vector instead. Elements can be added to it with e.g. push_back/emplace_back/insert/emplace member functions and it has a constructor taking an iterator range.

user177325220
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