Call by Value and Call by Reference in C

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S Subrata Sasmal 2 years 4 months ago
24 3 0

I'm trying to understand the conceptual difference between call by reference, value, and name.

So I have the following pseudocode:
<code>foo(a, b, c)
{
b =b++;
a = a++;
c = a + b*10
}

X=1;
Y=2;
Z=3;
foo(X, Y+2, Z);</code>
What's X, Y, and Z after the foo call if a, b, and c are all call by reference? if a, b, and c are call-by-value/result? if a, b, and c are call-by-name?

Another scenario:
<code>X=1;
Y=2;
Z=3;
foo(X, Y+2, X);</code>
I'm trying to get a head start on studying for an upcoming final and this seemed like a good review problem to go over. Pass-by-name is definitely the most foreign to me.

Reference - https://www.scaler.com/topics/c/call-by-value-and-call-by-reference-in-…

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3 Replies

S Sean Kennedy

This article may be more relevant to your understanding, since this shows some demonstrable outputs based on the input conditions.

https://www.javatpoint.com/call-by-value-and-call-by-reference-in-c

S Sean Kennedy

Just to also ring ones noodles - with RUST programming language - this is left a little Vague.
( the older documentation has the FAQ - the newer site here: does not...)
https://prev.rust-lang.org/en-US/faq.html#why-no-stable-abi

Really most Rustaceans learn rust via this portal: https://doc.rust-lang.org/stable/rust-by-example/

v vineet jadav

I will break down this pseudocode based on different parameter passing mechanisms by taking this example: 

foo(X, Y+2, Z);

If parameters are passed by reference:

  • X is passed by reference, so its value will change to whatever a becomes.
  • Y+2 is an expression, not a variable, so it cannot be passed by reference.
  • Z is passed by reference.

After the function call, X will be updated to 11 (since a is 1 and a++ is 2, then c = 1 + 2*10 = 21 and X will be assigned 21), Y and Z remain unchanged.

If parameters are passed by value/result:

  • X, Y+2, and Z are all passed by value/result.
  • The values of X, Y, and Z remain unchanged because the function operates on copies of the values.

If parameters are passed by name:

  • The function is essentially pasted into the code wherever it's called, with its parameters substituted directly.
  • X will be updated to 11 (as per the call-by-reference scenario).
  • Y+2 and Z will remain unchanged because they are not modified within the function.

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