CODEWITHSUNDEEP
c++vector
Oriol
Oriol

Reputation: 288550

How can I set a vector in C++ and all its data at the same time?

I wrote some JavaScript code but now I want to translate it to C++ because of perfomance, but my knowledge of C++ is low.

In JavaScript I can do:

var arr=[[['à','á'],['è','é'],['ì','í'],['ò','ó'],['ù','ú']],['a','e','i','o','u']];

How can I do something like that in C++? Must I do

vector<vector<char>> arr;

and then set each element manually?

arr[0][0]='à';
arr[0][1]='á';
...

Upvotes: 2

Views: 433

Answers (5)

Johannes S.
Johannes S.

Reputation: 4626

Alternatively, you could use std::vector< std::pair< char, char > >.

Note, that you cannot use operator[](ie. call arr[0] or arr[0][0] on an empty vector (since the requested elements are not there, you access invalid memory which (hopefully) will crash your program). Add elements to a vector with push_back(...):

vector< pair< char, char > > arr;
arr.push_back( make_pair( 'à','á' ) );
arr.push_back( make_pair( 'è','é' ) );
arr.push_back( make_pair( 'ì','í' ) );
arr.push_back( make_pair( 'ò','ó' ) );
arr.push_back( make_pair( 'ò','ó' ) );
arr.push_back( make_pair( 'ù','ú' ) );

Depending on what you want to do, std::map< char, char > might be useful for you as well. It will allow you to access elements using the first type as a key, eg.

std::map<char, char > mymap;
mymap['à'] = 'á';
// will print "Element à = à"
cout << "Element à = " <<  mymap['à']  << endl;

Upvotes: 2

Loki Astari
Loki Astari

Reputation: 264621

This will work for C++11

std::vector<std::vector<char>> var arr={{'à','á'},{'è','é'},{'ì','í'},{'ò','ó'},{'ù','ú'},{'a','e','i','o','u'}};
// Note it is changed from the original I removed one level of nesting from part of the array.

If you are using C++03.
Then you need to change things slightly.

std::string var[] = {"àá'", "èé", "ìí", "òó", "ùú", "aeiou"};

The types have changes but it has the same affect and access to the object var is unchanged.

Upvotes: 2

Guy Adini
Guy Adini

Reputation: 5494

Here's a code snippet using c++0x:

#include <vector>
#include <iostream>
using namespace std;

int main(){
    vector< vector<char> > v = { {'a','b','c'}, {'d','e','f'} };
    for (unsigned i=0; i<v.size(); i++){
        cout <<"Subvector: ";
        for (unsigned j=0; j<v[i].size(); j++)
            cout << v[i][j];
        cout << endl;
    }

    return 0;
}

Compile it with g++ -std=c++0x

Upvotes: 0

Qaz
Qaz

Reputation: 61970

Yes, it's at least a bit more work unless you have C++11, which adds the possibility of constructors taking an initializer list:

std::vector<std::vector<char>> arr {{'a', 'b'}, {'c', 'd', 'e'}, {'f'}};

You might also consider replacing std::vector<char> with std::string.

Upvotes: 7

SingerOfTheFall
SingerOfTheFall

Reputation: 29966

Unfortunately you can't initialize a vector as an array. However, you can initialize a vector with an array. For a single vector:

static const int arr[] = {1,2,3,4};
vector<int> vec (arr, arr + sizeof(arr) / sizeof(arr[0]) );

Initializing a vector of vectors is a little tricky, but you can do it in a cycle either like above, or like this: (pseudocode):

for( int i =0; i < something; i++ )//the outer vector
{
    vector.pushBack( std::vector<int> );
    for( int j =0; j < somethingElse; j++)
        vector[i].push_back(j);
}

Upvotes: 1

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