Incrementing a pointer is technically supposed to increment it by whatever size of thing that its pointing at. Void points at nothing, so the size is unknown. Its a nicety for some compilers to let you increment void pointers. Casting is annoying, because you have to either cast it to another pointer, and then back, … Read more
C doesn’t allow access to memory beyond the end of the array. It does, however, allow a pointer to point at one element beyond the end of the array. The distinction is important. Thus, this is OK: char array[N]; char *p; char *end; for (p = array, end = array + N; p < end; … Read more
*(ptr[x]) See the Wikipedia operator precedence table, or, for a more detailed table, this C/C++ specific table.
First, pointer arithmetic isn’t defined when performed on unrelated pointers. Second, it makes sense. When subtracting pointers you get the number of elements between those addresses, not the number of bytes. If you were to try that with char *p1 = &i, *p2 = &j; you would get a different result. As a side note, … Read more
No, it is legal. 5.7(4) – one paragraph before your quote – says: “For the purposes of these operators, a pointer to a nonarray object behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.”
Let’s take a trip back through the sordid history of OpenGL. Once upon a time, there was OpenGL 1.0. You used glBegin and glEnd to do drawing, and that was all. If you wanted fast drawing, you stuck things in a display list. Then, somebody had the bright idea to be able to just take … Read more
You should indeed be using ptr[i] over *(ptr + i) for readability reasons. But apart from that, the [] operator is, strictly speaking, actually never used with an array operand. Arrays, when used in an expression, always “decay” into a pointer to the first element (with some exceptions). C17 6.3.2.1/3, emphasis mine: Except when it … Read more
Like the ++ increment operator, the – subtraction operator with pointers also takes into account the size of the objects being pointed to. Specifically, the result returned is the number of bytes difference in the pointer values divided by the size of the pointed-to object (12, in your example). So the difference is 12 bytes, … Read more
Several answers here have stated that pointers are numbers. This is not an accurate description of pointers as specified by the C standard. In large part, you can think of pointers as numbers, and as addresses in memory, provided (a) you understand that pointer subtraction converts the difference from bytes to elements (of the type … Read more