1: Passing Arguments by Value
A copy of the variable is made and provided to the function when arguments are passed by value. All modifications made to the variable inside the function only affect the copy; nothing is changed to the original variable. As a result, passing by value is a secure method because there is no possibility of unintentionally modifying the value of the original variable.
Passing by value, however, might be ineffective, especially when dealing with big or complicated data types. Every function call requiring a copy of the data can quickly exhaust CPU and memory resources. Furthermore, passing by value cannot be used for functions that aim to change the value of the original variable because the copy and the original variable are not linked.
2: Passing Arguments by Reference
Variables can be passed by reference in C++ as well, which helps to solve these problems. The original variable is sent to the function when passing by reference, and any modifications performed to the variable inside the function will also affect the original variable. Because of this, passing by reference is substantially more effective for large or complicated data types and avoids the need for copying.
To prevent unintended modifications, a function must be explicitly designated as const. Adding the const keyword to the function declaration, as in “int calculate(const int& a, const int& b),” will accomplish this.
However, passing arguments by reference requires careful attention to detail as well. Inexperienced programmers can make mistakes, such as creating unintentional side effects, unintended sharing of data, and overriding external data.
Consider the following code that demonstrates both argument passing methods:
using namespace std;
void PassByValue(int x) {
x = 5;
cout << "Inside PassByValue: " << x << endl;
}
void PassByReference(int& x) {
x = 5;
cout << "Inside PassByReference: " << x << endl;
}
int main() {
int num1 = 2, num2 = 2;
cout << "Before function calls: num1= " << num1 << " num2= " << num2 << endl;
PassByValue(num1);
PassByReference(num2);
cout << "After function calls: num1= " << num1 << " num2= " << num2 << endl;
return 0;
}
In the above code, the first function, PassByValue, receives an integer argument by value. Within the function, a new integer variable is created and assigned the value 5. The original integer remains unmodified. The second function, PassByReference, receives an integer argument by reference. In this case, the function directly manipulates the original variable.
Output
As expected, the first call outputs 5, but has no effect on the original variable. In contrast, the second call changes the value of num2 to 5, which affects the output of the final statement.
Pass by Value vs. Pass by Reference
1: Way to Call a Function
One difference between passing by value and passing by reference is how the function is called. When passing by value, the function call must include the variable’s value, such as `calculate(a, b)`. When passing by reference, the function call must include the variable’s memory address, symbolized by an ampersand character, such as `calculate(&a, &b)`.
2: Data Types
In general, passing by value is most appropriate when working with small or simple data types, or when the function is not intended to modify the original variable. Passing by reference is more appropriate for large or complex data types, or when the function is intended to modify the original variable’s value.
Conclusion
When parameters are passed by value to a function, a copy of the variable is created and supplied. By passing by reference, the original variable is sent to the function. In C++, passing arguments by value or by reference is a fundamental concept. Choosing the right approach depends on the specific circumstances and should be carefully evaluated. The benefits of using the reference approach can result in more effective code, despite the temptation to use the easier passing by value method.
