Question

We learned that when calling subprograms or functions that we can pass data to the subprogram or function by ‘value’ or by ‘reference’. Describe what each approach is, how it works and what the potential security disadvantage is when passing parameters by reference.

Answer 1

When you pass parameters to a function, you can do so in two ways:

1. Pass by value
2. Pass by reference

When you pass a parameter to a function by value, then a copy of the variable is made in memory. When you access or modify the variable in the function, then only the copy of the variable is modified. The original variable is left untouched.

When you pass a parameter to a function by reference, you pass the memory address of the function, so it is the same variable being passed to the function. So when you modify the variable from the function the original value of the variable is changed too.  

When passing parameters by reference you are allowing the original value of the variable to be modififed, which in some cases might lead to a function changing the value even when the function is not intended to do so. The programmer will need to take special care to not accidentally modify the variable.

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