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When you pass a parameter by value, you are creating a copy of the original variable and the receiving (method/function) cannot change the original value. When you pass by reference you are passing a pointer to the original object and therefore any changes are made to the original value.

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โˆ™ 2009-05-26 14:27:08
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Q: What is the difference between pass by reference and pass by value in C?
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What is difference between pass by value and pass by reference in VB?

When an argument is passed by value, the function receives a copy of the argument. When you pass by reference, the function receives the address of the argument.


What is the difference between pass by value and pass by reference in java?

There is no explicit pass by value and pass by reference in Java. Internally Java does a pass by value of primitive data types like int, float etc and a pass by reference of object data types like business models or collections. This is Java's explicit behavior and we cannot influence Java to explicitly use pass by value or reference based on our wish.


Differences between pass by value pass by reference in java?

pass by value is the technique where a copy of the variable is passed to the method as argument. This value can be modified inside the method but that would not affect the original value. Pass by reference is the technique where the reference to the actual variable is passed to the method as argument. Any changes to this variable would affect and alter the original value. Usually primitive data types are passed by value and objects are passed by reference in java.


What are the different parameter passing methods used by c plus plus?

Pass by value, constant value, reference and constant reference. Pass by value is the default in C++ (pass by reference is the default in Java).


What is the difference between passing by value and passing by difference?

Passing by value is where you pass the actual value (be it an integer, an array, a struct, etc.) to a function. This means that the value must be copied before the function is called and therefore the value in the caller cannot be modified within the callee. Passing by reference is where a reference/pointer to a value is passed to a function. The reference often takes up less space than copying the actual value (particularly when the value is a struct or an array) and allows you to manipulate the value in the caller within the callee.


What are the differences between passing a parameter by value and by reference?

The best way to understand this is to use a programming language in which you can pass by either value or reference. When you pass by value, the parameter as the function uses it is a copy of the parameter that the calling function had. When you pass by reference, the parameter is actually an address in memory where something is. The function can either read this something, or it can also modify it.


What is the difference between pass by value and pass by reference in c?

Pass By Reference :In Pass by reference address of the variable is passed to a function. Whatever changes made to the formal parameter will affect to the actual parameters- Same memory location is used for both variables.(Formal and Actual)-- it is useful when you required to return more then 1 valuesPass By Value:- In this method value of the variable is passed. Changes made to formal will not affect the actual parameters.- Different memory locations will be created for both variables.- Here there will be temporary variable created in the function stack which does not affect the original variable.


How call by reference is different from call by value?

Pass by value creates a temporary copy of the object being passed. Pass by reference passes the actual object itself. If the parameter is declared constant, you can safely pass by reference. If it is declared non-constant, you should only pass by reference when you expect changes to the value to be reflected in the original object. Otherwise you should pass by value; only the copy is affected, not the original object.


What the difference between call by reference and call by value return in c plus plus?

In call by value, you can only pass values stored in variables and catch them in other variables, actual variables are mostly unaffected (value of only one variable can be modified in one call). In call by reference, you pass address of variables, so actual variables are modified (multiple values can be modified in one call).


What is the difference between passing by value and by reference with examples in C?

When you pass by value you pass a copy of the value. When you pass by reference, you pass the address of the value.void foo(int x){x*=2;} // pass by valuevoid bar(int &x){x*=2} // pass by referenceint main(){int y=1;foo(y);bar(y);return( 0 );}In the above example, calling foo(y) passes the value of y (1) which is then assigned to x in the function. x and y are separate variables so although foo() changes the value of x, this has no effect on y which is still 1 when the function returns.Calling bar(y), on the other hand, passes the address of y and assigns that address to the reference x. Both x and y refer to the same memory so when bar() changes the value of x it changes the value of y, thus y will be 2 when the function returns.Note that the only difference with pass by reference is that the parameter x has an ampersand to denote that it is a reference to the argument (addressof) rather than a local copy of the argument's value.Pass by reference is the preferred method of passing all complex objects to functions as there is no need to copy the object. Failure to do so will result in an often unnecessary overhead in calling the object's copy constructor. Where the function does not need to alter the object, the reference should be declared const. If it is non-const, the caller can fully expect any changes to be reflected in the original object. The only time a function should ever accept complex objects by value is when it must change the object but must not change the object that was passed. Passing by value ensures the function only works on a copy of the object.Note that pass by reference is not unlike pass by pointer. The only difference is that pointers must always be passed by value. To mimic passing a pointer by reference, you must pass a pointer to pointer instead.


What is a difference between passing by value and passing arguments by reference in visual basic 6 procedures?

When we pass arguments my value, we are passing the value represented in the variable mentioned in the call, and not the variable itself. Therefore, any modifications made to that value will NOT be reflected in the variable mentioned in the call. Pass by reference, as the name suggests passes the reference of the variable mentioned in the procedure call. Any modifications made to the data of that variable is changed at the memory location of that data itself, and will be reflected in the variable itself, after the procedures completes.


Explain the passing parameters as function in Call by Value and Call by Reference and then distinguish between them?

Call by value essentially passes a copy of an object's value whereas call by reference essentially passes the object itself. Pass by reference is the preferred method whenever possible as call by value will automatically invoke the object's copy constructor, which is often unnecessary, especially if the object is not affected by the function call (pass by constant reference).


What is the Difference between pass by reference and pass by value?

Pass by value calls a function or returns a value based on the number or "value". Maybe you're calling a function with the value of 5, you would just call the function passing the 5. The function can't change the 5, it's always a 5. Pass by reference calls a function and passes a pointer to a memory location that contains the value. You might call the function pointing to a location that contains the number of people who live in your home. That location has been populated with a value, so the function can look at that location and determine that yes, there are 5 members in your family. But the function may be responsible for updating the number of people in your family and you just had a baby, so the function would update the value that is stored at the location. Pass by reference just gives a "pointer" to the memory location. In reality, when a string value is used in any "C" application, it passed by reference.


What are the advantages of passing parameters by value in c plus plus?

You pass parameters by value when you do not want the original value to change. Passing by value creates a temporary copy of the value, only the copy is affected, but it can add some overhead to the function call, especially if the value is a complex structure or object. If you want any changes reflected in the original value, you must pass by reference instead. However, if the parameter is a constant reference, the object's immutable members are not altered. So when the option exists to pass by value or by constant reference, choose constant reference every time. Pass by non-constant reference only when you expect any changes to be reflected in the original value, otherwise pass by value.


Is array list value type or reference type?

Arrays are reference type. array values are always pass by reference.


Distinguish between passing argument to a function by value and passing by reference?

When you pass by value, the function's parameter is assigned the value of the argument that was passed. When you pass by reference, the function's reference parameter is assigned the address of the argument. In other words, pass by value copies the value, pass by reference passes the variable itself.Pass by reference is always the preferred method of passing arguments to functions when those arguments are complex objects. If the argument is a primitive data type then the cost in copying the value is minimal, but copying a complex object is expensive in terms of performance and memory consumption. If the function parameter is declare constant, you can be assured the object's immutable members will not be affected by the function. If it is non-constant and you do not wish your object to be altered, you can either copy the object and pass the copy, or pass the object by value if the function is overloaded to cater for this eventuality (good code will provide both options).


What do you mean by call by value and call by reference of a function?

In call by value a copy of the variables is passed to the function, whereas in call by reference the address of the variables is passed to the function. call by value and call by reference are terms used in Visual Basic but it is pass by value and pass by reference. This looks like a question for Visual Basic rather than C.


What are the advantages of pass by reference as compared to pass by value?

When you use passing by reference you save RAM because reference type doesn't create a copy of variable. stack overflow is avoided...


What are the differences between call by value and call by reference in c plus plus?

Pass by value copies the value whereas pass by reference passes the actual value. As a result, pass by reference is quicker. If a function does not need to alter the value being passed, then there's little point in passing it by value. A constant reference is a far better option. If the function does alter the value, and the changes are expected, a non-constant reference is the ideal choice. If changes are not expected, then either pass by value, or copy the value and then pass the copy by reference. Pointers are always passed by value (only the pointer is copied, not the object being pointed at), but they act like references. However, pointers should only be passed if there's ever a possibility of passing a pointer to NULL. If an object is guaranteed to exist, passing by reference is the method of choice. Passing by constant value is a pointless endeavour since the value is copied, and the copy will fall from scope when the function returns, and therefore has no effect on the actual parameter passed by the caller. However, if the value must remain constant within the function, declaring the formal parameter as a constant is no bad thing.


What are the possibe problems if you use call by value instead of call by reference?

When you pass by value you essentially pass a temporary copy of the value. If the value's parameter is declared const, then copying the value could be costly, especially if the value is a large and complex structure or object. If the value's parameter is non-const, then it has to be assumed the function intends to alter the value in some way. If you pass by value, only the copy will be affected, not the original value. When a parameter is declared constant, passing by reference is generally the way to go. When it is non-const, pass by reference if you fully expect any changes to be reflected in the original value, otherwise pass by value.


Is call by reference and pass by reference same thing?

Yes, they are the same thing -- both relate to how actual arguments are passed to a called function's formal arguments, with by value and by reference being the only two possibilities. The function determines which semantic to use. All programming languages support pass by value, which means you pass the value of the object, not the object itself. That is, the function works on an exact copy of the object. Pass by reference is achieved by passing the address of an object. The address is actually passed by value, thus the address is copied, not the object residing at that address. In C, pass by reference is achieved by declaring the function's formal argument as a pointer of the required type. Thus when you pass the address of an object, that address is copied to the formal argument. In C++, you can do the same thing, however C++ also supports the concept of references. A reference differs from a pointer in that a reference is not a variable (it has no storage of its own) it is simply an alias (an alternate name) for an existing object. As such a reference can never be null and cannot be reassigned once instantiated. In some respects, references act like constant pointers. The following functions demonstrate the difference: void byval (int i) { i*=2; } void byref (int& i) { i*=2; } void byptr (int* i) { *i *= 2; } int main() { int x = 42; byval (x); byref (x); byptr (&x); } The byval() function uses the pass by value semantic, thus we call by value. In other words, we pass the value of x (which is 42) and that value is assigned to the variable i. When we double i, x is left unchanged -- they are separate variables. The byref() function uses the pass by reference semantic, thus we call by reference. That is, we pass the address of x, and that address is assigned to the reference i. When we double the value of i, we double the value of x -- they are the same variable by different names (aliases). The byptr() function uses pass by value semantics, thus we call by value. That is, we pass the address of x by value, and that address is assigned to the pointer i. When we double the dereferenced value of i we double the value of x, since i points to x. That is, we get pass by reference semantics by passing addresses to pointers, by value.


What are the Parameter passing mechanisms in functions in c plus plus?

There are only two methods: pass by value and pass by reference. The function itself determines how arguments are passed into the function, as defined by the function signature. If the function accepts a reference, then the argument is passed by reference, otherwise it is passed by value. Pointers are always passed by value but behave like references. The only real difference is that pointer values may be NULL but references can never be NULL.


Difference between pass by value and pass by reference?

When you pass by value you pass a copy of the name. That is, the function's parameter is assigned the value of the name you pass. If the function parameter is a class type, then that class' copy constructor is called, automatically, which assigns the name's member value(s) to a new instance of the class. The function parameter is temporary, it has local scope, and will therefore fall from scope when the function returns. Thus any changes made to the local name within the function have no effect on the name you passed -- they are completely separate names. When you pass by reference you pass the name itself. To be precise, you pass the memory address of the name, its reference. This address is assigned to the function's reference parameter. Thus any changes made to the reference parameter's value will change the name you passed, since they both refer to the same memory address. Passing by reference is the most efficient method of passing objects (instances of a class) to functions as there is no overhead in copying the object. And if a reference parameter is declared constant then you can be assured the function will not alter the immutable members of the object (while there are ways around this, if a function really intends to alter a reference parameter then it should not be declared constant in the first place). Pass by value should only be used when the value is a primitive data type (generally equal to or smaller than a pointer), or when the function needs to alter the value but must not alter the name that was passed. Note that pointers are always passed by value, but since they can store a memory address they can be treated just as if they were references (assuming the pointer is non-zero of course). When passing pointers, the pointer and the address being pointed at can both be independently declared constant (that is, either, both, or neither can be constant). To pass a pointer by reference you must pass a pointer-to-pointer type, which is itself passed by value. This allows the function to not only modify the address being pointed at (making it point to another address), but to also modify the value at that address, just as if you'd passed the value by reference.


Explain the difference between passing a piece of data by value and passing a piece of data by reference?

Pass by value and pass by reference apply to functions that accept formal arguments. A formal argument may be a value or a reference. The function's caller uses actual arguments and the calling convention determines how an actual argument is assigned to the corresponding formal argument. If the formal argument is a value, then the value of the actual argument is assigned to the formal argument. If the formal argument is a reference, then the address of the actual argument is assigned to the formal argument. The nett effect is that when you pass by reference, both the formal and actual arguments refer to the same object. Whereas when you pass by value, the formal argument is a copy of the actual argument. Some languages, like C, do not support the notion of a reference argument and only use pass by value semantics. However, C does support the notion of a pointer data type which is a variable that can store a memory address. The value of a pointer is therefore a reference and passing a pointer by value is the same as passing by reference. This is because when a pointer value is assigned to another pointer, the address (the value of the pointer) is copied, thus the two pointers refer to the same object. C++ evolved from C and uses the same pass by value semantic by default. However, C++ also has a dedicated reference type that allows native pass by reference semantics. A reference differs from a pointer in that a pointer is a variable and therefore requires memory of its own to store the address it refers to. Thus a pointer has an address and a value, just like any other variable. But a reference does not have its own address because a reference is simply an alias, an alternate name for an object in memory. In other words, the address of a reference is the address of the object it actually refers to, in the same way that Billy could be alternate name for an object named William; they are one and the same object by different names. A pointer is not an alias, it is a completely separate object. Another key difference is that a reference cannot be reassigned, it must be initialised at the point of declaration. In this respect it is similar to the behaviour of constant pointer. Finally, a reference can never refer to a non-existent object, whereas a pointer can. When a pointer is no longer required it must be nullified by assigning it the value zero.


Why do you sometimes need to pass arguments to functions by reference?

You should always pass by reference unless there is good reason not to. Passing by reference always passes the object itself whereas passing by value always copies the object. Copying complex objects can severely impact upon performance which is why programmers try very hard to never pass anything larger than the CPU can cope with (typically 4 bytes on a 32-bit system and 8 bytes on a 64-bit system). Since a reference is effectively the address of an object and has the same length as a pointer, you can pass by reference either by passing a pointer or by passing an actual reference, depending on the function signature. The difference is that when you pass a pointer, the pointer is actually passed by value and is therefore copied. Also, pointers must also be dereferenced which incurs an extra layer of indirection that you do not incur when passing by reference. When you pass by reference you pass the object itself.