Question

I am reading some code sample that sounds odd to me:

Method argument is a pointer to double. In method body, there a conditional statement testing whether this argument pointer is given or not (empty or not). I wonder how the pointer can have a bool value, and what is the syntax for non-existant pointer (NULL? 0?).

Here is the method implementation :

bool OMethod::initSim(double* alpha_)
{
int i, j;
const double * cparameters = fun->getParameters();
simplex = OMatrix::allocMatrix(npts,ndim,true);
sSum = new double[ndim];
funcEvals = new double[npts]; 
double *alpha = 0;
     if(!alpha_) {
alpha = new double[ndim];
    for(i = 0; i< ndim; ++i) {
    if(cparameters[i] == 0)
        alpha[i] = 0.2f;
    else
        alpha[i] = 0.1 * cparameters[i];
        }
}
else
{
    alpha = alpha_;
}

     for(j = 0; j < npts; ++j) 
 {
    for(i = 0; i < ndim; ++i)
    sim[j][i] = cparameters[i]
      }

delete [] cparameters;

for(j = 0; j < ndim; ++j)
{
    sim[j + 1][j] += alpha[j];
}

computeS();

for(i = 0; i < npts; ++i) 
{
    funcEvals[i] = evalFunc(simplex[i]);    
    }

Answer 1

In C++, a pointer value is considered “true” in a boolean context (e.g. in an if test or ! expression) when it is not equal to zero, i.e. it is not null. So, !alpha is the same as alpha == 0, alpha == NULL and alpha == nullptr.