Vector of Structures

Question

I have some code given to me by another person in which we have a structure

struct Pair {
    string s1;
    string s2;
    bool equivalent;
  };

Then he sets up a vector of these structs hard coded

std::vector<Pair> PairID;

  staticdata() {
      PairID={{"string","string2",true}, 
      {"string","string3",true}, 
      {"string","string4",false}, 
      {"string","string7",false}, 
      {"string3","string8",false}
    };
    }

Unfortunately my compiler is complaining on the line PairID={{"string","string2",true},

Why is this? He suggested to compile using -std=c++0x but my compiler (gcc 4.2) does not support this. Is there an easy way to convert the code so it works? Why is it failing??

I am using Mac OSX and would prefer not to update my compiler

score 8 · Accepted Answer · answered Nov 11 '10 at 15:23

Your code is not legal C++. It is legal C++0x but there have been many changes to the language. So if you want to compile this code as C++ code, you'll need to change it.

PigBen's solution is one way, the problem with it being the temporary data could be constructed & destroyed many times, or live for a long time.

Here's another way:

    struct Pair {
        string s1;
        string s2;
        bool equivalent;
      };

    Pair make_Pair(const string& s1, const string& s2, bool equivalent)
    {
        Pair ret;
        ret.s1 = s1;
        ret.s2 = s2;
        ret.equivalent = equivalent;
        return ret;
    }

    // somewhere in the init code...
        std::vector<Pair> PairID;


   PairID.push_back(make_Pair("string","string2",true)); 
    PairID.push_back(make_Pair("string","string3",true));
    PairID.push_back(make_Pair("string","string4",false));
    PairID.push_back(make_Pair("string","string7",false));
    PairID.push_back(make_Pair("string3","string8",false));

Then again, the temporary data in PigBen's answer could be made into a constant static variable, which would therefore take less room and be faster to copy than your solution. — Victor Nicollet, Nov 11 '10 at 15:33
@Victor: To be sure, I would probably use a solution like PigBen's unless for whatever reason I didn't want to. — John Dibling, Nov 11 '10 at 15:34
@Victor: But I seriously doubt that in an optimized build PigBen's solution will be any faster than this. — John Dibling, Nov 11 '10 at 15:36

Konrad Rudolph · Answer 2 · 2022-10-19T14:26:51.957

7

Why is it failing?

Because it’s not valid C++ before C++11. Something quite close will be valid afterwards. But in C++03, it’s just not valid. And since your compiler doesn’t yet support C++11, you will need to do it the hard way, i.e. populate the vector one element at a time, or copy from a C array …:

Pair data[] ={ {"string","string2",true}, 
    {"string","string3",true}, 
    {"string","string4",false}, 
    {"string","string7",false}, 
    {"string3","string8",false} };
PairID.assign(data, data + sizeof data / sizeof *data);

edited Oct 19 '22 at 14:26

answered Nov 11 '10 at 15:17

Konrad Rudolph

530,221
131
937
1,214

Agreed. Turning this into an initialization from an array using `PairId.assign()` is probably what will require the least work. – Victor Nicollet Nov 11 '10 at 15:19
@Victor: `PairID.assign` is a nice hint, thanks. I’ve always just used `copy` with a `back_inserter` until now. – Konrad Rudolph Nov 11 '10 at 15:23

score 4 · Answer 3 · answered Nov 11 '10 at 15:19

void staticdata() {
    Pair temp[] =
    {
        {"string","string2",true}, 
        {"string","string3",true}, 
        {"string","string4",false}, 
        {"string","string7",false}, 
        {"string3","string8",false}
    };

    PairID.assign(temp,temp+5);
}

score 1 · Answer 4 · answered Nov 11 '10 at 15:33

1

You can use Boost.Assign, which is a syntactic sugar for creating a vector and then populating it:

using std::vector<int>;
using namespace boost::assign;
vector<int> v = list_of(Pair("s11", "s12", true)(Pair("s21", "s22", false));

answered Nov 11 '10 at 15:33

wilhelmtell

57,473
20
96
131

score 0 · Answer 5 · answered Jan 08 '18 at 05:31

0

struct Pair 
{
   string s1;
   string s2;
   bool equivalent;
};
std::vector<Pair> PairID;         

Pair pair;

pair.s1 = "abc";
pair.s2 = "abc";
pair.equivalent = TRUE;

PairID.push_back(pair);

answered Jan 08 '18 at 05:31

user9186396

1

score 0 · Answer 6 · answered Jul 08 '18 at 16:30

If you know the size of vector in advance then you can go for this

You can use any temporary instance of structure and assign the default values to that and then use a normal assignment like

typedef struct mystruct{
    int x;
    char name[10];
}mystruct;

mystruct default;
default.x = 1;
strcpy(default.name,"default_name");
vector <mystruct> v(10,default);

Vector of Structures

6 Answers6

Linked