A way of cycling through different vectors?

[mclemon]

Hi there!
I'm writing a program which has lots of vectors in it...I've named these vectors sequentially - ie vector1, vector2, vector3 etc.
What I was wondering is, is there a way of displaying the contents of these vectors without manually writing cout << vector1[0] etc?
I know this doesn't work but its essentially what I want to do:

number1[0] = 1;
    number2[0] = 2;
    number3[0] = 3;


    for(int i=1; i<=3; i++)
        cout << numberi[0];

I appologise in advance for my amateur-ness....it's for a university project and we haven't had the time to properly learn c++!
Thanks in advance!

[drkybelk]

For a start: it is no problem to create a vector of vectors which saves you naming each vector and instead use an index

typedef vector<vector<double> > DOUB_VEC_VEC;

DOUB_VEC_VEC myVecs;
myVecs.resize(3); // three vectors of doubles
myVev[0].push_back(2.4);
myVev[0].push_back(3.13);
myVev[1].push_back(5.0);
myVev[4].push_back(42.0);

cout << myVec[0][1] << endl; // displays 3.13

of course you can do this in a loop no problem

size_t numberOfvectors = 100; // 100 vectors
size_t vecSize[numberOfvectors]; // sizes of the individual vectors
// initialize all the differnt sizes...
//....

// set values
for(size_t vNum=0; vNum<numberOfvectors; vNum++)
{
    myVec[vNum].resize(vecSize[vNum]);
    for(size_t vInd=0; vInd < vecSize[vNum]; vInd++)
        myVec[vNum][vInd] = (double)(rand()%100); // set a rand value between 0..99
}

Does that answer your question?

[mclemon]

Thanks for your reply!
Yeah I think it does answer my question. Although I think I've reached the limit of my programming skills (even with your help) :P
Thanks a lot!

[thekashyap]

If you want fancy stuff use STL for_each.

So if you have 3 vectors to print then your code would look like this:

vector<int> vec1;
vector<char> vec2;
vector<float> vec3;
for_each (vec1.begin(), vec1.end(), print);
for_each (vec2.begin(), vec2.end(), print);
for_each (vec3.begin(), vec3.end(), print);

Even if you don't want fancy stuff, I recommend to readup the STL algorithms it makes your code much smaller in size.

[mclemon]

Yeah that looks like it could be very handy.
Thanks very much.

[vijayan121]

If the number of vectors which have elements on which you want to perform a particular operation (for example, print it) is fixed, you could write a simple wrapper function:

#include <algorithm>

template< typename SEQ1, typename SEQ2, typename SEQ3, typename FUNCTION >
inline void for_each( SEQ1& seq1, SEQ2& seq2, SEQ3& seq3, FUNCTION do_it )
{
    std::for_each( seq1.begin(), seq1.end(), do_it ) ;
    std::for_each( seq2.begin(), seq2.end(), do_it ) ;
    std::for_each( seq3.begin(), seq3.end(), do_it ) ;
}

If not, you could overload the function for two, three, four ... sequences.

Or if you are using a compiler with support for C++0x variadic templates (like g++ 4.5 or 4.6 with -std=c++0X):

#include <algorithm>

template< typename FUNCTION, typename SEQUENCE >
inline void apply( FUNCTION do_it, SEQUENCE& seq )
{  std::for_each( seq.begin(), seq.end(), do_it ) ; }

template< typename FUNCTION, typename FIRST_SEQ, typename ...OTHER_SEQS >
inline void apply( FUNCTION do_it, FIRST_SEQ& first, OTHER_SEQS ... rest )
{  apply( do_it, first ) ; apply( do_it, rest ... ) ; }

#include <vector>
#include <list>
#include <iostream>
#include <iomanip>

int main()
{
    std::vector<int> vec1 = { 0, 1, 2, 3, 4, 5 } ;
    std::vector<int> vec2 = { 9, 8, 7, 6, 4, 5 } ;
    std::vector<int> lst3( vec1.size(), 77 ) ;
    std::vector<int> lst4( vec1.rbegin(), vec1.rend() ) ;

    const int LINESZ = vec1.size() ;
    int cnt = 0 ;
    auto print_it = [ & cnt, LINESZ ] ( int value )
    {
        ++cnt ;
        std::cout << std::setw(3) << value << ( cnt%LINESZ == 0 ? '\n' : ' ' ) ;
    } ;

    apply( print_it, vec1, lst3 ) ;
    apply( print_it, vec1, vec2, lst3, lst4 ) ;
}