Pointers and fixed size buffers may only be used in an unsafe context

Question

I have 2 functions within a class and getting error on the call for ParseBits() function i.e. "int num_elements = ParseBits(bits, buffer);" because of the "buffer" arguement I am passing "public int ParseBits(string bits, int* buffer)":

Function 1:

public float AssignFitness(string bits, int target_value)
        {

   //holds decimal values of gene sequence
   int[] buffer = new int[(VM_Placement.AlgorithmParameters.chromo_length / VM_Placement.AlgorithmParameters.gene_length)];

   int num_elements = ParseBits(bits, buffer);

   // ok, we have a buffer filled with valid values of: operator - number - operator - number..
   // now we calculate what this represents.
   float result = 0.0f;

   for (int i=0; i < num_elements-1; i+=2)
   {
      switch (buffer[i])
      {
         case 10:

            result += buffer[i+1];
            break;

         case 11:

            result -= buffer[i+1];
            break;

         case 12:

            result *= buffer[i+1];
            break;

         case 13:

            result /= buffer[i+1];
            break;

      }//end switch

   }

   // Now we calculate the fitness. First check to see if a solution has been found
   // and assign an arbitarily high fitness score if this is so.

   if (result == (float)target_value)

      return 999.0f;

   else

      return 1/(float)fabs((double)(target_value - result));
   //   return result;
}

Function 2:

public int ParseBits(string bits, int* buffer)
        {

            //counter for buffer position
            int cBuff = 0;

            // step through bits a gene at a time until end and store decimal values
            // of valid operators and numbers. Don't forget we are looking for operator - 
            // number - operator - number and so on... We ignore the unused genes 1111
            // and 1110

            //flag to determine if we are looking for an operator or a number
            bool bOperator = true;

            //storage for decimal value of currently tested gene
            int this_gene = 0;

            for (int i = 0; i < VM_Placement.AlgorithmParameters.chromo_length; i += VM_Placement.AlgorithmParameters.gene_length)
            {
                //convert the current gene to decimal
                this_gene = BinToDec(bits.Substring(i, VM_Placement.AlgorithmParameters.gene_length));

                //find a gene which represents an operator
                if (bOperator)
                {
                    if ((this_gene < 10) || (this_gene > 13))

                        continue;

                    else
                    {
                        bOperator = false;
                        buffer[cBuff++] = this_gene;
                        continue;
                    }
                }

                //find a gene which represents a number
                else
                {
                    if (this_gene > 9)

                        continue;

                    else
                    {
                        bOperator = true;
                        buffer[cBuff++] = this_gene;
                        continue;
                    }
                }

            }//next gene

            //   now we have to run through buffer to see if a possible divide by zero
            //   is included and delete it. (ie a '/' followed by a '0'). We take an easy
            //   way out here and just change the '/' to a '+'. This will not effect the 
            //   evolution of the solution
            for (int i = 0; i < cBuff; i++)
            {
                if ((buffer[i] == 13) && (buffer[i + 1] == 0))

                    buffer[i] = 10;
            }

            return cBuff;
        }

I am getting 2 errors for this functions on the highlighted lines:

Error 1: The best overloaded method match for 'VM_Placement.Program.ParseBits(string, int*)' has some invalid arguments

Error 2: Pointers and fixed size buffers may only be used in an unsafe context

Answer 1

You need to enclose your function using raw pointers in an unsafe block.

unsafe 
{
 //your code
}

Answer 2

I had the same problem, but it wasn't solved by any of the other answers up here. I kept getting different errors.

Whatever functions use unsafe code simply need to be declared with the "unsafe" keyword.
For example:

static unsafe void myFunction(int* myInt, float* myFloat)  
{
    // Function definition
}

Personally, I was trying to do this when making a wrapper class.
For those interested, it ended up looking something like this:

using System.Runtime.InteropServices;

namespace myNamespace
{
    public class myClass
    {
        [DllImport("myLib.so", EntryPoint = "myFunction")]
        public static extern unsafe void myFunction(float* var1, float* var2);
    }
}

Theres a lot of great information in the MSDN "Unsafe Code Tutorial":
https://msdn.microsoft.com/en-us/library/aa288474(v=vs.71).aspx

It's probably worth a read, I found it quite useful.

Answer 3

Perhaps I've missed it, but you don't appear to be doing anything that actually requires the use of a int*. Why not simply pass it an int array and change the ParseBits function signature to:

public int ParseBits(string bits, int[] buffer)

and remove the unsafe{ ... } blocks altogether.