What are pass by value and pass by reference

Value passing is to pass a copy of the parameter to the function, so the function receives a copy of the parameter value, not the parameter itself. Any modification to the parameter inside the function will only affect this copy, not the parameter. will affect the value of the original variable. Pass by reference is to pass the address or reference of the parameter to the function. This means that the function receives a reference to the original data, not a copy of the data. Any modifications made to the parameters inside the function will directly affect the original data. These two delivery methods have their own applications, advantages and disadvantages in different programming languages ​​and scenarios.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Passing by value and passing by reference are two common ways of passing parameters, which are used in programming languages ​​to pass data from function to function. These two transfer methods have essential differences in processing data.

1. Value passing

Value passing is to pass a copy of the parameter to the function, so the function receives a copy of the parameter value, not the parameter itself. Any modifications to the parameters inside the function will only affect this copy, not the value of the original variable. Passing by value is often used on C and C's basic data types (such as int, float).

A key feature of value passing is that the function receives the actual value of the parameter, not a reference to the parameter. This means that when a function receives an argument passed by value, it actually operates on a copy of the argument value, rather than the original argument itself. Therefore, modifications to parameters within the function will not affect the value of the original variable.

For example, in C language, value passing can be achieved in the following way:

void increment(int a) {  
    a = a + 1;  
}  
  
int main() {  
    int x = 5;  
    increment(x);  
    printf("%d\n", x); // 输出仍然是5，因为函数increment操作的是x的副本，不影响x本身  
    return 0;  
}

In this example, the increment function receives an integer parameter a and modifies its value by adding 1 . However, this modification will not affect the value of the original variable x, because a is just a copy of x.

2. Passing by reference

Different from passing by value, Passing by reference passes the address or reference of the parameter to the function. This means that the function receives a reference to the original data, not a copy of the data. Any modifications made to the parameters inside the function will directly affect the original data.

A key feature of pass-by-reference is that a function receives a reference to the original data, not a copy of the data. This means that when a function receives an argument passed by reference, it is actually a direct reference to the original data, so any modifications to the argument will affect the original data.

In C, reference passing can be achieved by using pointers or references:

void increment(int* a) {  
    *a = *a + 1;  
}  
  
int main() {  
    int x = 5;  
    increment(&x);  
    std::cout << x << std::endl; // 输出是6，因为函数increment直接修改了x的值  
    return 0;  
}

In this example, the increment function receives a pointer a pointing to an integer and modifies it by dereferencing the pointer value of x. Since a is a reference to x, modifications to *a will directly affect the value of x. Therefore, when increment(&x) is called, the value of x is modified to 6.

In summary, the main difference between value transfer and reference transfer is: value transfer is to transfer a copy of the parameter value, and modification of the copy will not affect the original data; while reference transfer is to transfer a reference to the original data, Modifications to the reference will directly affect the original data. These two delivery methods have their own applications, advantages and disadvantages in different programming languages ​​and scenarios.

The above is the detailed content of What are pass by value and pass by reference. For more information, please follow other related articles on the PHP Chinese website!