Thread: memcpy strange

Here is the code:

Code:

    
	// set the array with values of 0
	for (int index = 0; index < NumElements -1; index++) {
		OriginalArray[index] = 0;
	}
	
	// forget about pure random at the moment
	for (int index = 0; index < NumElements -1; index++) {
		OriginalArray[index] = rand() % NumElements;
	}
  
    // stub for displaying numbers
	for (index = 0; index < NumElements -1; index++) {
	    cout << OriginalArray[index] << '\t';
    }
	
    // copy the OriginalArray to the global RandomArray
    memcpy(RandomArray, OriginalArray, NumElements-1);
    cout << "\n\n\n\n";
    
    // stub for displaying numbers
	for (index = 0; index < NumElements -1; index++) {
	    cout << RandomArray[index] << '\t';
    }

Here is some sample output:

Code:

6    4    3    9    6    4    1    0    6

// after 'copy'
6    4    3    0    0    0    0    0    0

What the? - rove

I cant figure out what is wrong, anyone see anything i cant?

Thanks for the input, but that seems to make it worse, now only displaying 1 random number and following 0's. Is there a way to copy one element at a time and just loop it?

The third argument to memcpy is the number of bytes to copy so you want:

Code:

    memcpy(RandomArray, OriginalArray, NumElements * sizeof(RandomArray[0]));

I'm suspicious of your use of NumElements - 1. Typically we don't want the - 1 because we are using the < operator and therefore for an array with 5 elements we get:

Code:

	for (int index = 0; index < 5; index++) {
		// index goes from 0 to 4
		OriginalArray[index] = rand() % NumElements;
	}

while with - 1 we get:

Code:

	for (int index = 0; index < 5 -1; index++) {
		// Index goes from 0 to 3
		OriginalArray[index] = rand() % NumElements;
	}