pass-by-value

This question already has an answer here: Is Java “pass-by-reference” or “pass-by-value”? 82 answers Beginner java question, but I cannot understand how call-by-Value ( or Reference ) is working in the example below - How come the String value is not modified after it exits the method while my custom String Object is. ? Same with other classes like Date.. public class StringMadness { public static void main(String[] args) { String s = "Native String"; CustomStringObject cs = new CustomStringObject(); System.out.println("Custom String Before: " + cs.str); hello(cs); System.out.println("Custom

i am new to C++ programming, when i am doing some C++ programs i have got a doubt that is why copy constructor is called when i pass an object as argument by value to a function. please see my below code in that i am passing a object of class as an argument by value to a function display() but it calling copy constructor and then control is hitting the display() function but i am understanding why it so please help. #include "stdafx.h" #include <iostream> using namespace std; class ClassA { private: int a, b; public: ClassA() { a = 10, b = 20; } ClassA(ClassA &obj) { cout << "copy constructor

Let's consider an object foo (which may be an int , a double , a custom struct , a class , whatever). My understanding is that passing foo by reference to a function (or just passing a pointer to foo ) leads to higher performance since we avoid making a local copy (which could be expensive if foo is large). However, from the answer here it seems that pointers on a 64-bit system can be expected in practice to have a size of 8 bytes, regardless of what's being pointed. On my system, a float is 4 bytes. Does that mean that if foo is of type float , then it is more efficient to just pass foo by

A simple question for which I couldn't find the answer here. What I understand is that while passing an argument to a function during call, e.g. void myFunction(type myVariable) { } void main() { myFunction(myVariable); } For simple datatypes like int , float , etc. the function is called by value. But if myVariable is an array, only the starting address is passed (even though our function is a call by value function). If myVariable is an object, also only the address of the object is passed rather than creating a copy and passing it. So back to the question. Does C++ pass a object by

If I pass a dataframe to a function and modify it inside the function, is it pass-by-value or pass-by-reference? I run the following code a = pd.DataFrame({'a':[1,2], 'b':[3,4]}) def letgo(df): df = df.drop('b',axis=1) letgo(a) the value of a does not change after the function call. Does it mean it is pass-by-value? I also tried the following xx = np.array([[1,2], [3,4]]) def letgo2(x): x[1,1] = 100 def letgo3(x): x = np.array([[3,3],[3,3]]) It turns out letgo2() does change xx and letgo3() does not. Why is it like this? The short answer is, Python always does pass-by-value, but every Python