C++ unordered_map no matching member function for call to 'find'

Question

I'm trying to initialize an unordered_map in c++ and then run the find command, it keeps failing with this error and I'm not sure what to do next. This is in leetcode if that helps.

string num = "10003";
unordered_map<string,string> mymap = {
            {"0","0"},
            {"1","1"},
            {"6","9"},
            {"8","8"},
            {"9","6"},
        };
        unordered_map<string,string>::const_iterator got;
        for (auto s: num){
            mymap.find(s);
        }

Line 15: Char 19: error: no matching member function for call to 'find'
            mymap.find(s);
            ~~~~~~^~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/unordered_map.h:920:7: note: candidate function not viable: no known conversion from 'char' to 'const std::unordered_map<std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>, std::hash<std::string>, std::equal_to<std::__cxx11::basic_string<char>>, std::allocator<std::pair<const std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>>>>::key_type' (aka 'const std::__cxx11::basic_string<char>') for 1st argument
      find(const key_type& __x)
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/unordered_map.h:924:7: note: candidate function not viable: no known conversion from 'char' to 'const std::unordered_map<std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>, std::hash<std::string>, std::equal_to<std::__cxx11::basic_string<char>>, std::allocator<std::pair<const std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>>>>::key_type' (aka 'const std::__cxx11::basic_string<char>') for 1st argument
      find(const key_type& __x) const
      ^
1 error generated.

@selbie simpler: `mymap.find(std::string{s});` or just `mymap.find({s});` — Remy Lebeau, Mar 08 '21 at 07:11

score 1 · Answer 1 · answered Mar 08 '21 at 07:17

The problem is that your key type is std::string, but you are passing a single char to find(). std::string does not have a constructor that accepts only a single char, hence the error.

There are other ways to construct a std::string from a char, eg:

mymap.find(std::string(1,s));

mymap.find(std::string(&s,1));

mymap.find(std::string() + s);

using std::literals;
mymap.find(""s + s);

mymap.find({s});

score 0 · Answer 2 · answered Mar 08 '21 at 06:09

0

s is of type char, while your map has key's of type string. Change one or the other.

answered Mar 08 '21 at 06:09

acraig5075

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C++ unordered_map no matching member function for call to 'find'

2 Answers2