This page contains examples of arrays and pointers in C programming language. C Program to Calculate Average Using Arrays: C Program to Find Largest Element of an Array. C String Functions; C String Examples. Strings as pointers: Another way of accessing a contiguous chunk of memory. The C library string.h has several common functions for dealing with strings. Strings as arrays, as pointers, and string.h. Why C has Pointers “What?” & “How. In C one can bodge up an such an array by. The program implements the Copy string to another string. The inner function “stcpy” takes 2 string pointers as arguments. C Program to Copy all elements of an array into Another array. C Program to Read integers into an array and Reversing them using Pointers; C Program to Implement Stack Operations Using. C Program to Copy String Without Using strcpy(). How to copy one string to other string using pointers in C? Can you write a c program to copy one string to another without using library function? ![]() Everything you need to know about pointers in CThis document comes with a companion example program, available as one file or as multiple files (zipped). Style used in this document. This is regular text. This is a variable, some code, and some sample output. Using Pointers with Arrays. The Basics of C Programming. Arrays in C are unusual in that variables a and b are not. This is a line of code. On current mainstream Intel processors, it occupies four bytes of memory (because an int is four bytes wide). Now let's declare another variable. We have initialized it to point to foo. As I said, foo occupies some memory. Its location in memory is called its address. The location of this box is its address. When you access the address, you actually access the contents of the box it points to. This is true of all variables, regardless of type. In fact, grammatically speaking, there is no such thing as a “pointer variable”: all variables are the same. There are, however, variables with different types. The pointer to foo is the contents of foo. You could put a different pointer in the foo. But it would no longer point to foo. The pointer has a type, too, by the way. Thus it is an “int pointer” (a pointer to int). An int **'s type is int * (it points to a pointer to int). The use of pointers to pointers is called multiple indirection. More on that in a bit. Interlude: Declaration syntax. The obvious way to declare two pointer variables in a single declaration is: int* ptr? It is not a pointer. C's declaration syntax ignores the pointer asterisks when carrying a type over to multiple declarations. If you split the declaration of ptr. This is the immediate improvement: int *ptr. It is now right next to the word ptr. A subtle implication of association. It's even clearer to put the non- pointer variables first: int ptr. Just use your own judgment. Finally, I should point out that you can do this just fine: int *ptr? This solution might be obvious: foo. In this example, the new value of foo. But we don't know that this points to anything, so it probably doesn't. Trying to access this address will probably result in a segmentation violation (read: crash).(Incidentally, compilers usually warn when you try to assign an int to a pointer variable. You must dereference it. Dereferencingint bar = *foo. This is called “decaying”: the array “decays” to a pointer. Most usages of array are equivalent to if array had been declared as a pointer. There are, of course, cases that aren't equivalent. One is assigning to the name array by itself (array = . 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) . This illustrates that you are really handling an array and not merely a pointer. In most uses, however, array expressions work just the same as pointer expressions. So, for example, let's say you want to pass an array to printf. 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. You can only give printf the pointer, not the whole array. In English, these expressions read “array”, “pointer to array”, and “pointer to the first element of array” (the subscript operator, . But in C, all three expressions mean the same thing.(They would not all mean the same thing if “array” were actually a pointer variable, since the address of a pointer variable is different from the address inside it—thus, the middle expression, & array, would not be equal to the other two expressions. The three expressions are all equal only when array really is an array.)Pointer arithmetic (or: why 1 == 4)Say we want to print out all three elements of array. The type of the pointer here is int. When you add to or subtract from a pointer, the amount by which you do that is multiplied by the size of the type of the pointer. In the case of our three increments, each 1 that you added was multiplied by sizeof(int). By the way, though sizeof(void) is illegal, void pointers are incremented or decremented by 1 byte. In case you're wondering about 1 == 4: Remember that earlier, I mentioned that ints are four bytes on current Intel processors. So, on a machine with such a processor, adding 1 to or subtracting 1 from an int pointer changes it by four bytes. But what does this have to do with pointers? This is another one of those secrets of C. The subscript operator (the . But remember that, in most contexts, arrays decay to pointers. This is one of them: That's a pointer you passed to that operator, not an array. As evidence, I submit: int array. Here's a diagram: array points to the first element of the array; array. You are correct: array. You create a structure type with the struct keyword, and a union type with the union keyword. The exact definitions of these types are beyond the scope of this article. Suffice to say that a declaration of a struct or union looks like this: struct foo . Unions have members too, but they're used differently. Accessing a member looks like this: struct foo my? Its dereference operator is a postfix ^. These two declarations are equivalent: const int *ptr. In the second example, the pointer itself is const; you can change *ptr. It confuses a lot of people, even C wizards. Bear with me. It's possible to take the address of a function, too. And, similarly to arrays, functions decay to pointers when their names are used. So if you wanted the address of, say, strcpy, you could say either strcpy or & strcpy. The function call operator takes a function pointer on its left side. In this example, we pass dst and src as the arguments on the interior, and strcpy as the function (that is, the function pointer) to be called: enum . These separate the asterisk indicating return type (char *) from the asterisk indicating the pointer level of the variable (*strcpy. You would use this in a cast. This part is really mind- bending, so stretch your brain a bit so as not to risk injury. In order to explain this, I'm going to summarize all the declaration syntax you've learned so far. First, declaring a pointer variable: char *ptr; This declaration tells us the pointer type (char), pointer level (*), and variable name (ptr). And the latter two can go into parentheses: char (*ptr); What happens if we replace the variable name in the first declaration with a name followed by a set of parameters? Huh. A function declaration. But we also removed the * indicating pointer level — remember that the * in this function declaration is part of the return type of the function. So if we add the pointer- level asterisk back (using the parentheses): char *(*strcpy. If this is a variable, and the first declaration was also a variable, can we not replace the variable name in THIS declaration with a name and a set of parameters? YES WE CAN! And the result is the declaration of a function that returns a function pointer: char *(*get. So the type returned by this function is char *(*)(char *, const char *) (with, again, the inner * indicating a pointer, and the outer * being part of the return type of the pointed- to function). You may remember that that is also the type of strcpy. There is no string type. C strings are really just arrays of characters: char str. This is how the end of the “string” is signaled. This idiom is the extent to which C has a string type. But that's all it is: an idiom. Except that it is supported by: the aforementioned string literal syntaxthe string library. The functions in string. But how can that be, if there is no string type? Why, they work on pointers. Here's one possible implementation of the simple function strlen, which returns the length of a string (not including the NUL terminator): size. That's because, despite the function's name, there is no “string” here; there is merely a pointer to at least one character, the last one being 0. Here's another possible implementation: size. Which, as we found out earlier, uses a pointer (not an array, and definitely not a string). Version history. 1. Fixed explanation of the relationship between Pointers and const. Added - > as one of the dereference operators in Multiple indirection. Changed improper use of . Most fonts still render the apostrophe (. Arrays are not pointers. Added two links to the right- left rule for reading C declarations. Corrected the name of the subscript operator (which I previously referred to as the index operator). Replaced references to the Power. PC with references to Intel processors. The previous versions (1.
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