#include <iostream>
#include <iterator>
#include <string>
#include <type_traits>
#include <vector>
 
template <typename C>
    using Value_Type = typename std::remove_reference<decltype(*std::begin(std::declval<C>()))>::type;
 
template<typename C, typename V>
std::vector<Value_Type<C>*> find_all(C& cont, V v) 
{
    std::vector<Value_Type<C>*> res; 
 
    for (auto& x : cont) 
        if (x == v) 
            res.push_back(&x);
 
    return res;
}
 
int main()
{
	std::string m{"Mary had a little lamb"}; 
	for (const auto p: find_all(m,'a'))
    	std::cerr << *p; 
    std::cerr << "\n";
}

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