CODEWITHSUNDEEP
c++stringc++11dictionarycompiler-errors
MMoRe
MMoRe

Reputation: 29

error: invalid user defined conversion from char to const key_type&

I am trying to assign int type value to each letter in latin alphabet using std::map. When I want to create new int and give it a value equal to int mapped to word, i get an error:

F:\Programming\korki\BRUDNOPIS\main.cpp|14|error: invalid user-defined conversion from 'char' to 'const key_type& {aka const std::basic_string&}' [-fpermissive]|

Example:

#include <iostream>
#include <string>
#include <cstdlib>
#include <map>

using namespace std;

int main()
{
    std::map <std::string,int> map;
    map["A"] = 1;
    int x;
    std:: string word = "AAAAAA";
    x = map[word[3]];

    cout << x;

    return 0;
}

What am I doing wrong?

Upvotes: 2

Views: 3613

Answers (3)

max66
max66

Reputation: 66230

I am trying to assign int type value to each letter in latin alphabet using std::map.

So you have to use char (instead of std::string) as key of the map; something like

#include <iostream>
#include <string>
#include <map>

int main()
{
    std::map<char, int>  map;
    map['A'] = 1;
    int x;
    std:: string word = "AAAAAA";
    x = map[word[3]];

    std::cout << x << std::endl;

    return 0;
}

As observed by others, now you're trying to use a char as a key for a std::map where the key is a std::string. And there isn't an automatic conversion from char to std::string.

Little Off Topic suggestion: avoid to give a variable the same name of a type, like your std::map that you've named map. It's legit but confusion prone.

Upvotes: 2

gsamaras
gsamaras

Reputation: 73444

word[3] is of type char, and your map has a key of type std::string. There is no conversion from char to std::string.

Just take the substring of the string (by using string::substr), by changing this:

x = map[word[3]];

to this:

x = map[word.substr(3, 1)];

Or better yet, use char as your key, since you need letters, like this:

std::map <char, int> map;
map['A'] = 1;
// rest of the code as in your question

Upvotes: 1

Jerry Jeremiah
Jerry Jeremiah

Reputation: 9643

word[3] is a character at the fourth position of the string. But you can't use that as a key for the map because the map uses a string as it's key. If you change the map to have a key of char then it will work or you can:

  • create a string from the word[3]
  • use substr(3,1) to get the key

Upvotes: 0

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