new operator with parentheses "(", ")" instead of brackets "[", "]"

Question

I found a crazy mistake in my code.

I had written the following line:

GLfloat* points = new GLfloat(1024);

rather than

GLfloat* points = new GLfloat[1024];

I only just noticed it. My code has compiled and run a few times before I noticed the error. I realize that this is by fluke, but my question is what does the line I originally had do?

I notice that it looks kind of like the creation of a class using a pointer to allocated memory. Does it create a single GLfloat on the heap with the initial value of 1024.0? If this is true, why is it valid syntax? (GLfloat is not a class, is it?)

Answer 1

what does the line I originally had do?

 GLfloat* points = new GLfloat(1024);

Let us try to replace GLfloat with int, you will see that if GLFloat is a type similar to int or float, then you will have the following:

int * points = new int(1024);

The above statement means that you are creating a pointer to an int with initial value being 1024. So in your case, it means creating a pointer points to a variable with type being GLfloat and initial value as 1024.

It is equivalent to write the following in a condensed version:

int * points = new int;
*points = 1024;

See here for more explanation.

Answer 2

GLfloat is an OpenGL alias for float (i.e., typedef float GLfloat;). Consequently the code:

GLfloat* points = new GLfloat(1024);

Is equivalent to:

float* points = new float(1024);

Which allocates a floating point number and initializes it to 1024.0 and assigns its address to pointer points.

Answer 3

Yes, you are creating a single GLFloat on the heap initialized to 1024.0. You can initialize primitives with the same syntax as classes. e.g.

int i(10);

Would create an int on the stack initialized to 10.