passed by reference or pointer ?

[vohu]

Hello,

I have a question : in C language, can we pass value by reference, as we do in C++ language ?

For example :
I know the method with pointers :
int myfunction (int *var) //like that

and, I saw in C++, we can use the method by reference with & :
int myfunction (int &var)

there is the same thing in C language, isn't it ?

[jimblumberg]

I have a question : in C language, can we pass value by reference, as we do in C++ language ?

No pass by reference is only valid in C++.

Jim

[manasij7479]

No, C doesn't have references, you have to pass pointers.
Btw, you've got C++ references wrong too.

[Subsonics]

Btw, you've got C++ references wrong too.

How? The only thing mentioned was the use of an ampersand.

[manasij7479]

How? The only thing mentioned was the use of an ampersand.

My mistake, I did not see that it was a declaration and automatically thought it was a call by the absence of a semicolon.

[oogabooga]

In C you simulate pass by reference with pointers.

void func(int * const n) {
    *n = 42;
}
// elsewhere
int x = 41;
func(&x);

[Subsonics]

In C you simulate pass by reference with pointers.

void func(int * const n) {
    *n = 42;
}
// elsewhere
int x = 41;
func(&x);

I wouldn't call that a very convincing simulation, since pointers are available in C++ as well. The difference is that you have to remember the level of indirection and dereference accordingly. References in C++ is more like an alias, so the reference can be treated as if it is what it references. I'm not saying this because I think you aren't aware of it btw, just to say that IMO they are a different thing.

[MK27]

Hello,

I have a question : in C language, can we pass value by reference, as we do in C++ language ?

Formally no, because C has pointers -- most languages that use pointers do not use references and vice versa.

Pointers provide more functionality than references but are slightly more complicated to use, which is why C++ incorporated references.

// with pointers
void myfunc (int *x);  // prototype
int n;
myfunc(&n);   // call

// with references
void myfunc (int &x);  // prototype
int n;
myfunct(n);

The second style is simpler and less prone to error. Because pointers allow you to do things you cannot do with a reference (such as arithmetic with memory addresses), where this functionality is undesirable, a reference would be considered "safer".

[manasij7479]

Because pointers allow you to do things you cannot do with a reference (such as arithmetic with memory addresses), where this functionality is undesirable, a reference would be considered "safer".

One can always grab the address of the referenced variable..

[MK27]

In C you simulate pass by reference with pointers.

It might be better to think of it the other way around: a reference simulates one common use for a pointer. "Pass by reference" is simply a conceptualization expressing this use-value.

One can always grab the address of the referenced variable..

Right, then you have a pointer. The point of the reference is abstraction. This is generally considered a good thing, which is why most languages which employ references don't provide such a mechanism (I think C++ is probably unique here).

[laserlight]

It might be better to think of it the other way around: a reference simulates one common use for a pointer. "Pass by reference" is simply a conceptualization expressing this use-value.

Yeah, if you're coming from an understanding of C++ references (admittedly likely to be the case for vohu), otherwise "a reference simulates one common use for a pointer" does not make sense since pointers are "references" in a computer science perspective: "pass by reference" or "call by reference" is a parameter passing method in computer science that is implemented in C++ by reference parameters and simulated in C and C++ by pointer parameters. Hence we talk about "dereferencing a pointer" to obtain what the pointer points to.

[vohu]

Finaly, the reference simplify the use of pointers ?

[laserlight]

Finaly, the reference simplify the use of pointers ?

In C++, yes, you can look at it in that way.

[vohu]

and, the expression "pass by reference" in C langage is a malapropism...I read that php language use automatic passing reference, this functionnality is integrated in C++11 ?

[laserlight]

the expression "pass by reference" in C langage is a malapropism.

It depends on your point of view. As I said, a pointer is a reference. I agree with saying that call by reference is "simulated" when passing a pointer because an explicit dereference is required, otherwise all that happens is that the pointer is passed by value; nonetheless the pointer refers to what it points to.

I read that php language use automatic passing reference

No, unless otherwise specified, arguments in PHP are passed by value. However, since PHP5, an object variable actually contains a reference to the object, not the object itself, i.e., it is an object reference, so you can see it as a pointer without pointer syntax.

this functionnality is integrated in C++11 ?

No, in C++, an object variable really does contain an object.