CODEWITHSUNDEEP
c++arraysstruct
Banderi
Banderi

Reputation: 710

Initialize a vector of customizable structs within an header file

Is there any way to have a list of global structs and initialize a vector containing modified version of them from within the same header file? I know I can't directly access and edit variables from an .h file, since it's not run-time code, but maybe there happens to be a workaround to this - or maybe some very basic way that I just happened to skip on the C++ Beginners manual.. pardon me if so!

To make an example, let's say I have a struct which comprehends a couple of members, and declared some global ones in the .h file..

struct MyStruct
{
  unsigned int a;
  string foo;
  float myfloat;
};

MyStruct struct_one={1,"hello",0.238f};
MyStruct struct_two={10,"salve",3.14f};
MyStruct struct_three={3,"bonjour",0.001f};
MyStruct struct_four={6,"dias",5.0f};

I can then initialize a vector containing them this way (don't know if it's the best one though)

MyStruct MyStructArray[] = {struct_one, struct_two, struct_three, struct_four};

vector<MyStruct> MyStructVector(MyStructArray,
MyStructArray+sizeof(MyStructArray)/sizeof(MyStructArray[0]));

But I would like to be able to change, on the fly, some of the structs' members before creating the vector (or the array) without changing the global ones. Possible?

EDIT: By "within an header file" I meant, "within an header file". If I do unsigned int a = 100; in the header, I don't have to initialize or call something in the actual source to make it work. The vector by itself works perfectly, I only wanted to know if there was a way to build it from modified versions of the original global structs.. say, I want to use the same global structs, but with different values for member a.

Upvotes: 3

Views: 2102

Answers (2)

andre
andre

Reputation: 7249

On top of @Sam 's answer...

Use a constructor:

struct MyStruct {
    unsigned int a;
    string foo;
    float myfloat;

    MyStruct(unsigned int a, const string& foo, float myfloat) : a(a) , foo(foo), myfloat(myfloat) {}
};

Now you can add your struct to the vector with a simple statement 

vec.push_back(MyStruct(1, "hello", 0.238f));

class Foo {
public:
    static std::vector<int> MyStructVector;
}

inline std::vector<MyStruct> MakeVector()
{
    std::vector vec;
    vec.push_back(MyStruct(1, "hello", 0.238f));
    //...
    return vec;
}

std::vector<MyStruct> Foo::MyStructVector= MakeVector();

Upvotes: 2

user2249683
user2249683

Reputation:

I do not know if i get your question right:

#include <vector>
#include <iostream>

// Header
// ======

struct MyStruct
{
  unsigned int a;
  std::string foo;
  float myfloat;

  MyStruct(unsigned a, const std::string& foo, float myfloat)
  : a(a), foo(foo), myfloat(myfloat)
  {}
};

typedef std::vector<MyStruct> MyStructs;

extern MyStructs& get_structs();

struct AppendToMyGlobalMyStruct {
    AppendToMyGlobalMyStruct(unsigned a, const std::string& foo, float myfloat) {
        get_structs().push_back(MyStruct(a, foo, myfloat));
    }
};


// Source
// ======

// Have initialization done at first function call, only:
MyStructs& get_structs() {
    static MyStructs s;
    return s;
}

// Another source
AppendToMyGlobalMyStruct a(0, "0", 0);
// Another source
AppendToMyGlobalMyStruct b(1, "1", 1);
// Another source
AppendToMyGlobalMyStruct c(2, "2", 2);

int main()
{
    MyStructs& s = get_structs();
    std::cout << s[0].foo << std::endl;
    std::cout << s[1].foo << std::endl;
    std::cout << s[2].foo << std::endl;
    return 0;
}

(names with my are stupid)

Upvotes: 0

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