11/5/2022 0 Comments Pointers cursors![]() ![]() You can only give printf the pointer, not the whole array. You can't: When you pass an array as an argument to a function, you really pass a pointer to the array's first element, because the array decays to a pointer. So, for example, let's say you want to pass an array to printf. In most uses, however, array expressions work just the same as pointer expressions. This illustrates that you are really handling an array and not merely a pointer. #Pointers cursors mac os x#The result will be the total size of the array, not the size of a pointer (for example, sizeof(array) using the array above would evaluate to ( sizeof(int) = 4) × 3 = 12 on a current Mac OS X system). One is assigning to the name array by itself ( array = …)-that's illegal.Īnother is passing it to the sizeof operator. There are, of course, cases that aren't equivalent. Most usages of array are equivalent to if array had been declared as a pointer. This is called “ decaying”: the array “decays” to a pointer. One neat feature of C is that, in most places, when you use the name array again, you will actually be using a pointer to its first element (in C terms, &array). This variable, array, is an extra-big box: three ints' worth of storage. int *array would be illegal here the compiler would not accept us assigning the initializer to it. Note that we use the notation because we are declaring an array. Here's a declaration of a three- int array: This is not useful for anything, except to declare function pointers (described later).įurther reading: The right-left rule for reading C declarations. Incidentally, C allows zero or more levels of parentheses around the variable name and asterisk: ![]() Just use your own judgment.įinally, I should point out that you can do this just fine: The absolute clearest is to keep every declaration on its own line, but that can take up a lot of vertical space. It's even clearer to put the non-pointer variables first: It's possible to do the single-line declaration in a clear way. #Pointers cursors plus#Think of it as assigning each variable a base type ( int), plus a level of indirection, indicated by the number of asterisks ( ptr_b's is zero ptr_a's is one). If you split the declaration of ptr_a and ptr_b into multiple declarations, you get this: It is not a pointer.Ĭ's declaration syntax ignores the pointer asterisks when carrying a type over to multiple declarations. Given this, what is the type of ptr_b? int *, right? then you can declare multiple int-pointer variables by simply giving the int-pointer type ( int *) followed by a comma-separated list of names to use for the variables ( ptr_a, ptr_b).and a single declaration can declare multiple variables of the same type by simply providing a comma-separated list ( ptr_a, ptr_b),.If the type of a variable containing a pointer to int is int *,.The obvious way to declare two pointer variables in a single declaration is: The use of pointers to pointers is called multiple indirection. An int **'s type is int * (it points to a pointer to int). Thus it is an “ int pointer” (a pointer to int). You could put a different pointer in the foo_ptr box, and the box would still be foo_ptr. The point of that is that the pointer is not the variable! The pointer to foo is the contents of foo_ptr. (Thus, “pointer variable” really means “variable of a pointer type”.) ![]() There are, however, variables with different types. In fact, grammatically speaking, there is no such thing as a “pointer variable”: all variables are the same. This is true of all variables, regardless of type. When you access the address, you actually access the contents of the box it points to. ![]() foo is a box that is sizeof(int) bytes in size. &foo is the address of foo (which is why & is called the “address-of operator”). Its location in memory is called its address. We have initialized it to point to foo.Īs I said, foo occupies some memory. On current mainstream Intel processors, it occupies four bytes of memory (because an int is four bytes wide).įoo_ptr is declared as a pointer to int. ![]()
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