C++ simple array creation with user given length

Question

How to create one array in a method with user given length? I would like to fill in a vector with user given length with random numbers.

 double* Random::quasiRandomUnif(float a, float b, int NN) 
 {
     int i, errcode;

          N_=NN; // here initialize the member N_

          float r[N_];

     VSLStreamStatePtr stream;
     int i, errcode;

     errcode = vslNewStream( &stream, BRNG,  SEED );
     errcode = vsRngUniform( METHOD, stream, N_, r, a, b );

     double* rd = new double[m_N];
     for(int i=0;i<m_N;i++)
         rd[i]=(double)r[i];

     errcode = vslDeleteStream( &stream );

     return rd;
  }

I thought of N_ a member for the class Random, to be initialized in this function's body, with some user given value -- not possible, since space allocated in array should be a constant. How to deal with?

Kind regards.

If m_N is not known at compile time then you should allocate r as you did for rd. Remember to delete them or use them with auto_ptr. — Paolo Brandoli
– Paolo Brandoli, Commented Apr 19, 2012 at 14:15
@PaoloBrandoli You can't store a dynamically allocated array in an auto_ptr - that would be undefined behaviour when the auto_ptr is destroyed, since it'll call delete instead of delete []. std::vector is the way forward here — Ben Cottrell
– Ben Cottrell, Commented Apr 19, 2012 at 14:18

laurent · Accepted Answer · 2012-04-19 14:14:28Z

5

In C++, you should use the vector class:

std::vector<double> rd;
for(int i=0;i<m_N;i++) rd.push_back(r[i]);

answered Apr 19, 2012 at 14:14

laurent

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Dervall · Accepted Answer · 2012-04-19 14:13:11Z

0

Use the new operator.

float r = new float[m_N];

Remember to delete it, when you are done with it.

delete[] r;

answered Apr 19, 2012 at 14:13

Dervall

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Steve Townsend · Accepted Answer · 2012-04-19 14:18:03Z

0

Try Boost.ScopedArray. Simpler semantics than vector without the memory management overhead of your own raw array.

answered Apr 19, 2012 at 14:18

Steve Townsend

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Some programmer dude · Accepted Answer · 2012-04-19 14:18:12Z

0

I guess the problem is with the r array? Why not allocate that with new as well? Then you can use any expression you like as the size.

answered Apr 19, 2012 at 14:18

Some programmer dude

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