Question

#define ARRAY_SIZE 20

float DataSource[ARRAY_SIZE];

void Read(unsigned char const *Source, unsigned char *Destination, unsigned long DataSize)
{
  for ( unsigned long i = 0; i < DataSize; i++)
  {
    *(Destination + i*DataSize) = *(Source + i*DataSize);
  }
}

void fun()
{
  int Index;
  float Dest;

  for ( Index = 0; Index < ARRAY_SIZE; Index++ )
  {
    Read((unsigned char *)&DataSource[Index], (unsigned char *)&Dest, sizeof(DataSource[Index]));
  }
}

I’m having an issue with the above code where upon calling Read(), my Index variable gets overwritten and I am certain the ugly pointer casting is the culprit, but I’m having trouble understanding exactly what is happening here.

The unsigned char pointer types are mandatory because the above code is intended to simulate some driver level software and maintain the same prototype.

Can someone help me to understand the issue here? All the above code is changeable except for the prototype of Read().

Answer 1

The error is here:

for ( unsigned long i = 0; i < DataSize; i++)
{
  //              vvvvvvvvvv               vvvvvvvvvv
  *(Destination + i*DataSize) = *(Source + i*DataSize);
}

i * DataSize is always greater than i => “out of bound” access.

Replace with:

for ( unsigned long i = 0; i < DataSize; i++)
{
  *(Destination + i) = *(Source + i);
}