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When you pass an object to a function you are not actually passing the object, you are only passing the object's value. This is what is meant by the term pass by value.
When passing a value to a function there are actually two objects involved in the exchange: the actual argument (the object that is being passed) and the formal argument (the object used by the function). When we call a function that accepts one or more arguments (also known as parameters), the value of the actual argument is assigned to the corresponding formal argument. Thus the formal argument is a copy of the actual argument and any changes made to the formal argument will have no effect upon the actual argument.
When the formal argument is a pointer, however, the value we pass is a memory address. The actual argument can either be a pointer of the same type or we can take the address of an object of the same type using the address-of operator and pass that. Either way, the value we pass is a memory address. We call this pass by reference even though the address is actually being passed by value. Passing by reference means that the formal argument and the actual argument both refer to the same object and offers an efficient means of passing large objects that are too expensive to copy. This includes most structures and unions and all arrays. Note that arrays implicitly decay to pointers and therefore cannot be passed by value. Structures and unions can be passed by value, but if they are larger than a pointer (in bytes) passing by reference is more efficient.
There are four different ways to declare a formal argument as a pointer:
- mutable pointer to mutable type
- mutable pointer to constant type
- constant pointer to mutable type
- constant pointer to constant type
Ideally, functions should declare formal pointer arguments using methods 2 or 4. Both point to constant types so this gives the caller an assurance that the function has no side effects upon the object being passed by reference. Functions that use methods 1 or 3 should be regarded as having side-effects upon the object being referred to. This can be desirable for efficiency reasons, however returning values via arguments (also known as output parameters) should be avoided whenever possible.
Note that it makes no difference if the formal pointer argument is mutable or constant because the formal and actual arguments are still separate objects. Constant formal arguments are only of relevance to the function designer, they are of no importance to the caller. This is true of all values passed to functions whether the value is a memory address or not. What is important to the caller of a by reference function is whether or not the object being pointed at is declared constant or not.
Wiki User
∙ 7y ago
Wiki User
∙ 12y agoNo references in C, so simply pass the address of the structure.
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What is the difference between passing an array and passing single value data to a function?
Passing a single value to a function is often just a simple integer. But passing an array, character string or other data structure is typically "pass by reference", or in other words, the calling statement will 'point to' the place in memory where the data structure resides.When a function is called using a pointer to a data structure, both the calling environment and the called function are referencing the same data; any changes made to the data in the structure by the function will have changed the data that the original calling environment sees.However, when a value is passed to a function, the function creates it's own copy of the value, and can change it in any way without changing the original value.
Which is the syntax used for passing a structure member as an argument to a function?
You can pass the address by using '&' with the pointer variable, while passing actual arguments. In formal arguments '*' is used in the place of '&'. To pass the address of a pointer variable a double pointer variable should be used .
How are Structure passing and returning implemented by the complier?
When structures are passed as arguments to functions, the entire structure is typically pushed on the stack, using as many words as are required. (Programmers often choose to use pointers to structures instead, precisely to avoid this overhead.) Some compilers merely pass a pointer to the structure, though they may have to make a local copy to preserve pass-by-value semantics. Structures are often returned from functions in a location pointed to by an extra, compiler-supplied ``hidden'' argument to the function. Some older compilers used a special, static location for structure returns, although this made structure-valued functions non-reentrant, which ANSI C disallows
Different types of pointers in c language?
... are usable. void pointer (generic pointer) : a special type of pointer which point to some data of no specific types. void *p; null pointer : a special type of pointer which point nowhere. it is usually used to check if a pointer is pointing to a null or free the pointer during deallocation of memory in dynamic memory allocation; it is define by using the predefine constant NULL int *p=NULL; wild pointer : uninitialized pointer. it hold a garbage value. i.e it is not pointing to any memory location yet. dangling pointer: pointer pointing to a destroyed variable. it usually happen during dynamic memory allocation when the object is destroyed but not free and the pointer is still pointing to the destroy object.
What is double hashing in data structure?
if collision is occurred in hash function then we can solve this problem by using double hash function
What is the difference between passing an array and passing single value data to a function?
Passing a single value to a function is often just a simple integer. But passing an array, character string or other data structure is typically "pass by reference", or in other words, the calling statement will 'point to' the place in memory where the data structure resides.When a function is called using a pointer to a data structure, both the calling environment and the called function are referencing the same data; any changes made to the data in the structure by the function will have changed the data that the original calling environment sees.However, when a value is passed to a function, the function creates it's own copy of the value, and can change it in any way without changing the original value.
When do you use pointers in C?
There are many uses of pointer in C. Pointers are efficient and elegant to use. All string variables are pointers, and calling a function using a pointer allows the function to change the value globally. These are what you can do with pointers in C. 1) Returning multiple values by passing address of variables. eg. foo(&a,&b,&c); 2) When you want to modify the value passed to function. eg. scanf() function. int n; scanf("%d",&n); /* pass address of variable n so that scanf can change its value*/ 3) When you need to pass large data structure to function, it is more efficient to pass pointer to structure than passing the entire structure. If you don't want to modify the structure members, you can use 'const' keyword which the ANSI-complaint C compiler will either warn or give error if you modify. eg strlen(const char *str) in string library should not modify the content of str. 4) Implementing 'goto' data structures are easy with pointers. eg. linked-list,binary trees, hash table. 5) You can allocate dynamic memory using pointers. 6) Pointers to function are used for call back function and jump table. eg qsort() and bsearch() functions require the caller to provide pointer to function to do the comparison.
Call by reference using pointer in c plus plus?
Example: void foo( MyClass& object ){} // function with call by reference signature MyClass* p = new MyClass(); // instantiate a pointer to MyClass foo( *p ); // call by reference using the pointer
Which is the syntax used for passing a structure member as an argument to a function?
You can pass the address by using '&' with the pointer variable, while passing actual arguments. In formal arguments '*' is used in the place of '&'. To pass the address of a pointer variable a double pointer variable should be used .
How are Structure passing and returning implemented by the complier?
When structures are passed as arguments to functions, the entire structure is typically pushed on the stack, using as many words as are required. (Programmers often choose to use pointers to structures instead, precisely to avoid this overhead.) Some compilers merely pass a pointer to the structure, though they may have to make a local copy to preserve pass-by-value semantics. Structures are often returned from functions in a location pointed to by an extra, compiler-supplied ``hidden'' argument to the function. Some older compilers used a special, static location for structure returns, although this made structure-valued functions non-reentrant, which ANSI C disallows
Why you are using VOID in C programming?
You don't use 'VOID', but 'void'. It means different things, such as:- void as function type means no return value- void as function parameter means no parameters- 'void *' as pointer-types means generic pointer
Which operator require to call c function using object name?
The operator required to call c function using object name is function object. Other operator names that deal with objects are structure dereference, structure reference, and indirection
Different types of pointers in c language?
... are usable. void pointer (generic pointer) : a special type of pointer which point to some data of no specific types. void *p; null pointer : a special type of pointer which point nowhere. it is usually used to check if a pointer is pointing to a null or free the pointer during deallocation of memory in dynamic memory allocation; it is define by using the predefine constant NULL int *p=NULL; wild pointer : uninitialized pointer. it hold a garbage value. i.e it is not pointing to any memory location yet. dangling pointer: pointer pointing to a destroyed variable. it usually happen during dynamic memory allocation when the object is destroyed but not free and the pointer is still pointing to the destroy object.
What is double hashing in data structure?
if collision is occurred in hash function then we can solve this problem by using double hash function
Does C even have pass by reference?
Strictly speaking, no. All arguments in C are passed by value. However, when the argument being passed is a memory address, although the address itself is passed by value, we're effectively passing the object that resides at that address -- by reference. Thus when a function's formal argument is a pointer variable (of any type), then it can be taken as read that the function is using the pass by reference semantic rather than the pass by value semantic. Nevertheless, it is important to keep in mind that the formal argument is assigned a copy of the actual argument and is therefore being passed by value.
How can an individual structure member be accessed in terms of its corresponding pointer variable?
By dereferencing the pointer variable. This can be achieved in two ways: typedef struct s { int i; float f; }; void f (struct s* p) { int x = p->i; /* using pointer to member operator */ float y = (*p).f; /* using dereference operator */ } The two methods are functionally equivalent.
How is an array name interpretedwhen it is passed to a function?
An array is still an array, regardless of how you pass it into functions. It is still an array-type variable at the beginning of a function. However, the function itself may manipulate the array by "imploding" it into a string with a delimiter, using array values with only specific keys, and such.
