CODEWITHSUNDEEP
c++c++11
InfernoFun
InfernoFun

Reputation: 1

Function Template not working, getting error "No suitable user-defined conversion"

I am trying to use a container (std::vector, std::list, std::map, etc...) on a function template but I keep getting an error saying "No suitable user-defined conversion exists"

I tried making a different function template, print_container() with 1 argument, and it works.

#include "stdafx.h"
#include <iostream>
#include <vector>

template<typename T>
using Iterator = typename T::iterator;

template<typename C, typename V>
std::vector<Iterator<C>> find_all(C& container, V value) {
    std::vector<Iterator<C>> res;
    for (auto p = container.begin(); p != container.end(); ++p)
        if ((*p) == value)
            res.push_back(p);
    return res;
}

int main() {
    std::vector<int> vec1 = { 1, 2, 3 };
    std::vector<Iterator<int>> res = find_all(vec1, 1); // does not work
    return 0;
}

find_all() should return a std::vector of iterators with only 1 iterator, the iterator attached to vec1[0] and assign that vector to res.

Upvotes: 0

Views: 97

Answers (3)

Vlad from Moscow
Vlad from Moscow

Reputation: 310990

The template argument of the Iterator in this declaration

std::vector<Iterator<int>> res = find_all(v, 1);

Is invalid. The type int has no iterators. See this alias declaration

template<typename T>
using Iterator = typename T::iterator;

You should write either

std::vector<Iterator<std::vector<int>>> res = find_all(v, 1);

or

auto res = find_all(v, 1);

Upvotes: 1

R Sahu
R Sahu

Reputation: 206607

The return type is std::vector<Iterator<std::vector<int>>>, not std::vector<Iterator<int>>.

std::vector<Iterator<std::vector<int>>> res = find_all(vec1, 1);

Use of auto is better for cases like this.

auto res = find_all(vec1, 1);

Upvotes: 2

max66
max66

Reputation: 66200

The problem is in the returned type

std::vector<Iterator<int>> res = find_all(vec1, 1);
//...................^^^ wrong

From that call you obtain a vector of iterators of std::vector<int>, not of int 

std::vector<Iterator<std::vector<int>>> res = find_all(vec1, 1);
//...................^^^^^^^^^^^^^^^^  correct

To avoid this sort of problems, usually you can use auto (starting from C++11)

auto res = find_all(vec1, 1);

Upvotes: 2

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