Pass by value/reference

Hi

In the following example, is the variable integer being passed by reference or by value?

Code:

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void test(int* var) {
    *var++;
}

int main() {
    int integer = 1;
    test(&integer);
    printf("%d", integer);
    return 0;
}

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The reason why I ask is because according to Pass By Value - Definition, pass by reference is not possible in C (since there are no references).

Best,
Niles.

The variable named integer is not passed at all. Rather, the address of the variable named integer is passed by value. This is used to simulate passing the variable named integer by reference.

Quote:

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Originally Posted by Niels_M

according to Pass By Value - Definition, pass by reference is not possible in C

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This is true - all function arguments are passed by value. However, the variable integer is not what's being passed - what's being passed is the address of the variable "integer". This address is indeed being passed by value, so you could say it's "simulating" pass-by-reference.

Hi. I dont understand why.

Quote:

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according to Pass By Value - Definition, pass by reference is not possible in C

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I thought variables could be either passed by Value/Reference?

Reference - Taking reference from original variable's address
Value - Taking concurrent value of particular variable

Quote:

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Originally Posted by Inneart

I thought variables could be either passed by Value/Reference?

Reference - Taking reference from original variable's address
Value - Taking concurrent value of particular variable

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Yes, and then there are other parameter passing schemes that are possible. However, that does not mean that all those parameter passing schemes are directly available in every programming language.

It's really misnamed. It's not pass-by-reference. It's pass-by-address. The address of the variable is copied into the function.
Pass-by-value copies the variable value into the function.

So in C language, variables are always passed by duplicating its value?

C = 5
Pass C to a F(x)
C of F(x) duplicates value of C

And if I want it to modify the original C,

C = 5
Pass &C to a F(x)
C of F(x) chops address of original C

Is that right?

Chops off?
The last example passes the address of C to F(x), allowing F(x) to write to the address instead of the local C to reflect the changes to the caller.

Chop as in take.

So my examples are correcto?

In that case, yes.

Quote:

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Originally Posted by laserlight

The variable named integer is not passed at all. Rather, the address of the variable named integer is passed by value. This is used to simulate passing the variable named integer by reference.

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So pass by reference is just the adress being passed by value? So it is OK so say that C has pass by reference as well?

Pass by reference is a concept and not a language feature. So in a sense, it is OK to do that.
I think it's silly, though. Clearly it isn't passing by reference, since the address is passed.
Furthermore, C++ also has a pass-by-reference language feature.

Conclusion: whether it is acceptable or not is up to you.

Quote:

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Originally Posted by Elysia

Pass by reference is a concept and not a language feature. So in a sense, it is OK to do that.
I think it's silly, though. Clearly it isn't passing by reference, since the address is passed.
Furthermore, C++ also has a pass-by-reference language feature.

Conclusion: whether it is acceptable or not is up to you.

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So what happens when we in C++ have pass-by-reference (I know how to pass a variable by reference, but what actually happens)? Does the address get copied or what?

It's pass-by-reference. The new variable in the function is an alias of the one you passed in. That is what the standard says.
In practice, it is usually implemented using pointers. But again, it doesn't have to be.
Thus, it is really a "true" pass-by-reference feature.

Quote:

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Originally Posted by Niels_M

So pass by reference is just the adress being passed by value? So it is OK so say that C has pass by reference as well?

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Basically that's all that pass by reference is in any language... you're giving the address of the variable instead of the value of the variable. C is just more honest about it.