How to use a vector of structs in a vector structs in c++?

Question

I want to create a vector of trains, where each train needs a vector of pairs.

If I run the code outside of main(), I get these errors:

naive-bayes.cpp:17:15: error: template argument 1 is invalid
    vector<pair> pairs;

naive-bayes.cpp:17:15: error: template argument 2 is invalid

Inside main(), I get these errors:

naive-bayes.cpp:22:15: error: template argument for 'template<class>
class std::allocator' uses local type 'main()::pair'
    vector<pair> pairs;

naive-bayes.cpp:22:15: error:   trying to instantiate 'template<class> class std::allocator'

naive-bayes.cpp:22:15: error: template argument 2 is invalid

Here is the code:

struct pair {
    int index;
    int value;
};

struct trains {
    string label;
    vector<pair> pairs;
};

Did you #include <vector>? And are you using namespace std? — Khalil Khalaf
– Khalil Khalaf, Commented Apr 15, 2017 at 0:41
And, if you have using namespace std, you are asking for trouble if you ever #include <utility> since there is a templated std::pair. Even worse, with some implementations, some standard header files include each other even when the standard doesn't require it. — Peter
– Peter, Commented Apr 15, 2017 at 0:47

Remy Lebeau · Accepted Answer · 2017-04-15 01:26:01Z

3

You're problem is probably due to using namespace std;.

There is a std::pair type in the standard library.

Try this:

#include <string>
#include <vector>

struct pair {
    int index;
    int value;
};

struct trains {
    std::string label;
    std::vector<pair> pairs;
};

int main()
{
    return 0;
}

edited Apr 15, 2017 at 1:26

Remy Lebeau

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answered Apr 15, 2017 at 0:44

21koizyd

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Comments

Patrick Kelly · Accepted Answer · 2017-04-15 00:50:45Z

2

Without a full program example to play with, all I can really point out is that your local pair declaration is likely getting confused with std::pair. Change your definition of struct pair to be struct mypair.

edited Apr 15, 2017 at 0:50

answered Apr 15, 2017 at 0:47

Patrick Kelly

1,4411 gold badge18 silver badges27 bronze badges

3 Comments

Peter Over a year ago

struct mypair and mypair will be equivalent in C++.

Patrick Kelly Over a year ago

@Peter - Is that true? Oops! Just tried that out here and you are indeed correct. Thanks for the correction. Will update

21koizyd Over a year ago

yep, it's second solution :)

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