C++ how to initialize a vector

[erotavlas]

Hi,

I have a simple question. How can I initialize the following vector?


std::vector<std::vector<std::pair<std::vector<std::pair<std::string, int> >, double> > > myVector;
I would like to have 5 elements (for example) inside of myVector. i.e. the outer vector of myVector should be of size 5.
I think that the following way is not the only one.


std::vector<std::pair<std::vector<std::pair<std::string, int> >, double> > tempVector(0);
for (int i = 0; i < 5; ++i)
{
myVector.push_back(tempVector);
}
What are the other ways?

Thank you

[ziekfiguur]

You could use the constructor: std::vector(size_type n, const T& value= T(), const Allocator& = Allocator());
It initializes the vector with its content set to a repetition, n times, of copies of value.

Just one remark though, i think it would be better to define a class than to use std::vector<std::pair<std::vector<std::pair<std::string, int> >, double> > as a datatype. It would certainly make your code a lot more readable and easier to understand. If you don't want to do that, you could also define a typedef for it so you don't have to repeat the whole thing every time in your code.

[erotavlas]

You could use the constructor: std::vector(size_type n, const T& value= T(), const Allocator& = Allocator());
It initializes the vector with its content set to a repetition, n times, of copies of value.

Just one remark though, i think it would be better to define a class than to use std::vector<std::pair<std::vector<std::pair<std::string, int> >, double> > as a datatype. It would certainly make your code a lot more readable and easier to understand. If you don't want to do that, you could also define a typedef for it so you don't have to repeat the whole thing every time in your code.

Thank you for your fast answer. Can you tell me how I can do your solution?

Can I use my code without using the tempVector?


std::vector<std::pair<std::vector<std::pair<std::string, int> >, double> > tempVector(0);
for (int i = 0; i < 5; ++i)
{
myVector.push_back(tempVector); // myVector.push_back(0) ????
}

[ziekfiguur]

since that constructor uses T() as a default argument i think you should just be able to use:

std::vector<std::vector<std::pair<std::vector<std::pair<std::string, int> >, double> > > myVector(5);
i haven't tested it though, maybe you would have to use

..blahblah... myVector(5, tempVector);

[dwhitney67]

Is this not easier to digest, that is, clearer to read?


struct Data
{
std::string str;
int val;
};

struct Data2
{
std::vector<Data> data;
double dbl;
};

std::vector<Data2> myVector;

If you want to initialize the 'myVector' to have 5 elements:


std::vector<Data2> myVector(5);

[nvteighen]

dwhitney67's solution points to a general approach you should always take in account when programming: repeated code is usually a symptom of insufficient/incorrect abstraction. This is valid in all programming languages, no matter what paradigm; of course the solutions may vary from one language to another, but the general idea is always the same: avoid repetitions by creating new concepts that allow further simplification of your code.