map<string, string> how to insert data in this map?

Question

I need to store strings in key value format. So am using Map like below.

#include<map>
using namespace std;
int main()
{
    map<string, string> m;
    string s1 = "1";
    string v1 = "A";

    m.insert(pair<string, string>(s1, v1)); //Error
}

Am getting below error at insert line

error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string'

I tried make_pair function also like below, but that too reports the same error.

m.insert(make_pair(s1, v1));

Pls let me know what's wrong and what's the solution for above problem. After solving above problem, can i use like below to retrieve value based on key

m.find(s1);

Etienne de Martel · Accepted Answer · 2010-09-14 12:55:29Z

42

I think you miss a #include <string> somewhere.

answered Sep 14, 2010 at 12:55

Etienne de Martel

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3 Comments

bjskishore123 Over a year ago

This made the code compiled. But am wondering why it didn't give error when i said string s1 = "1"; Only upon calling insert it gives error.

ereOn Over a year ago

@bjskishore123: Perhaps you have another class whose name is string that somehow collides with std::string ?

SonarJetLens Over a year ago

I have tested this on the latest VS 2012 version and it does the same thing. It's very confusing and peculiar that it doesn't complain about string not being defined.

Daren Thomas · Accepted Answer · 2010-09-14 12:58:30Z

10

Could you try this:

#include<string>

It seems the compiler doesn't know how to compare strings. Maybe she doesn't know enough about strings yet, but is too focused on your map to figure that out ATM.

answered Sep 14, 2010 at 12:58

Daren Thomas

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1 Comment

Filip OvertoneSinger Rydlo Over a year ago

Oh, interesting! Is the compiler she? Allright, I can agree on that. :) - Just like our Mother Nature and Milkyway Galaxy (in Sanskrit: Shi-shu-maa-ra = She-dolphin).

Alexey Tkach · Accepted Answer · 2018-12-20 08:04:46Z

7

Here is the way to set up map<...,...>

static std::map<std::string, RequestTypes> requestTypesMap = {
   { "order",       RequestTypes::ORDER       },
   { "subscribe",   RequestTypes::SUBSCRIBE   },
   { "unsubscribe", RequestTypes::UNSUBSCRIBE }
};

answered Dec 20, 2018 at 8:04

Alexey Tkach

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Comments

tdammers · Accepted Answer · 2010-09-14 12:53:58Z

5

Try m[s1] = v1; instead.

answered Sep 14, 2010 at 12:53

tdammers

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1 Comment

John Dibling Over a year ago

And this gives you no way to tell if you inserted a new node or updated a pre-existing one.

TadejP · Accepted Answer · 2018-09-08 14:22:23Z

4

You have several possibilities how store strings in key value format now:

m["key1"] = "val1";
m.insert(pair<string,string>("key2", "val2"));
m.insert({"key3", "val3"}); // c++11

And traverse it in c++11:

for( auto it = m.begin(); it != m.end(); ++it )
{
  cout << it->first; // key
  string& value = it->second;
  cout << ":" << value << endl;
}

answered Sep 8, 2018 at 14:22

TadejP

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1 Comment

Zeeshan Ali Khan Over a year ago

m.insert({"key3", "val3"}); // c++11 helped me

default · Accepted Answer · 2010-09-14 13:25:11Z

1

I think it has to do with the fact that <map> doesn't include <string>, but <xstring>. When you are adding elements to the map it needs to find the correct position in the map by sorting. When sorting, map tries to locate the operator <, from which it finds the correct location for the new element. However, there is no operator < for the definition of string in <xstring>, thus you get the error message.

answered Sep 14, 2010 at 13:25

default

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Comments

badrequest · Accepted Answer · 2016-03-14 13:46:39Z

-1

The s1 is an integer you are hoping pass as string...thats likely the main cause of the error!!

answered Mar 14, 2016 at 13:46

badrequest

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