How to map 2 char* arrays directly into std::map<std::string,std::string>

Question

I have 2 char arrays like "const char *arr1[ArrSize] = {"Blah1", "Wibble1", "Shrug1"};". For putting them into a vector I found a nice quick solution:

void fillVecTest()
{
    const int ArrSize = 3;
    const char *arr1[ArrSize] = {"Blah1", "Wibble1", "Shrug1"};
    const char *arr2[ArrSize] = {"Blah2", "Wibble2", "Shrug2"};
    std::vector<std::string> vec1(arr1, arr1+ArrSize);
    std::vector<std::string> vec2(arr2, arr2+ArrSize);
    std::vector<std::string>::iterator l_It1Vec1;
    std::vector<std::string>::iterator l_It = vec1.end();
    l_It = find(vec1.begin(), vec1.end(), std::string("Blah1"));
    if(l_It != vec1.end())
    {
      size_t l_pos = l_It - vec1.begin();
      printf("found %s, pos=%u val: %s\n", l_It->c_str(),l_pos, vec2[l_pos].c_str());
    }
 }

Now I thought it should be also possible to put both directly into a map as arr1 is the key and arr2 is the value. I tried some ways but I didn't succeed.

void fillMapTest()
{
    const int ArrSize = 3;
    const char *arr1[ArrSize] = {"Blah1", "Wibble1", "Shrug1"};
    const char *arr2[ArrSize] = {"Blah2", "Wibble2", "Shrug2"};
    std::map<std::string,std::string> map1;//(pair(arr1,arr1), pair(arr1+ArrSize,arr2+ArrSize));
    std::map<std::string,std::string>::iterator l_It1Map1;
    //l_It1Map1 = find(map1.begin(), map1.end(), std::string("Blah1"));
    if(l_It1Map1 != map1.end())
    {
      printf("found key: %s, val: %s\n",l_It1Map1->first.c_str(), l_It1Map1->second.c_str());
    }

}


int _tmain(int /*argc*/, _TCHAR* /*argv[]*/)
{
  fillVecTest();
  fillMapTest();
  return 0;
}

I think that just the commented lines in function "fillMapTest" would need to be solved. Constuctor and find don't work like I want.

Please has any STL expert an idea?

I forgot to say that I use C++98 and I'm looking first for the constructor solution, if there any. e.g std::map<std::string,std::string> map1(pair(arr1,arr1), pair(arr1+ArrSize,arr2+ArrSize)); — Alf-SW
– Alf-SW, Commented May 14, 2013 at 18:07

leemes · Accepted Answer · 2013-05-14 17:18:41Z

5

The easiest way to write this:

std::map<std::string, std::string> m {
    { "key1", "value1" },
    { "key2", "value2" },
};

This requires your compiler to support initializer lists (a feature of C++11).

edited May 14, 2013 at 17:18

leemes

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answered May 14, 2013 at 17:03

Kerrek SB

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11 Comments

leemes Over a year ago

@MatsPetersson I think it's time to assume people have a C++11 compiler (at least C++0x). If they want to support C++03, they should mention it in the question (my personal opinion). Is there a meta discussion about that?

leemes Over a year ago

Here it is...

Mike DeSimone Over a year ago

C++11 support is still getting phased in. gcc 4.8 was released a couple weeks ago and still doesn't have all the new features. And it still requires you to explicitly request C++11 with -std=c++11.

Qaz Over a year ago

@MikeDeSimone, We're getting pretty close with GCC and Clang's current statuses.

Qaz Over a year ago

@leemes, This isn't in MSVC. The library hasn't been updated for the CTP, and only the CTP has initializer lists.

|

andre · Accepted Answer · 2013-05-15 14:02:49Z

3

std::map<std::string, std::string> m;

for(int i = 0; i < ArrSize; i++) {
    std::pair<std::string, std::string> p =
        std::make_pair(std::string(arr1[i]), std::string(arr2[i]));
    m.insert(p);
}

If you really want to use the map constructor you need an iterator of pairs and the only way(i know) is to use a std::vector<std::pair<std::string, std::string> >::iterator but this seems to be an unneeded extra step to get the same result.

#include <vector>
#include <map>
#include <string>

std::vector<std::pair<std::string, std::string> > values;

for(int i = 0; i < ArrSize; i++) {
    std::pair<std::string, std::string> p =
        std::make_pair(std::string(arr1[i]), std::string(arr2[i]));
    values.push_back(p);
}

std::map<std::string, std::string> m(values.begin(), values.end());

edited May 15, 2013 at 14:02

answered May 14, 2013 at 17:06

andre

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4 Comments

Mike DeSimone Over a year ago

If you have C++11 handy, you can replace std::pair<std::string, std::string> with auto. Or, in either C++, you could just write m.insert(std::make_pair(std::string(arr1[i]), std::string(arr2[i])));

andre Over a year ago

@MikeDeSimone Agreed, in c++11 I would use KerrekSB's solution. But nothing in op's code indicates c++11, and I just wanted to be clear for OP what's happening in the code so I added the extra variable p.

leemes Over a year ago

I agree in keeping this answer C++03-compatible. So we have a C++11 and a C++03 solution.

Alf-SW Over a year ago

Nice solution and I'll hope it takes me further but the final goal is to get a similar solution just to use the map-constructor like I did with vector.

tzwickl · Accepted Answer · 2013-05-14 17:20:42Z

0

for(int i = 0; i < ArrSize; i++) {
    m.insert(pair<string, string>(arr1[i], arr2[i]));
}

answered May 14, 2013 at 17:20

tzwickl

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2 Comments

Alf-SW Over a year ago

Nice solution but I still hope to find a similar solution just to use the map-constructor like I did with vector.

Alf-SW Over a year ago

Now I had time to try it, but get an compile error. error C2665: 'std::pair<_Ty1,_Ty2>::pair' : none of the 3 overloads could convert all the argument types

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