CODEWITHSUNDEEP
c++arraysparameter-passing
FreshAir
FreshAir

Reputation: 301

A pathological way of passing an array: by reference to the first element

It seems one can pass an array by reference to the first element:

void passMe(int& firstElement)
{
    int* p=&firstElement;
    cout << p[0] << p[1];
}

Main program:

int hat[]={ 5,2,8 };
passMe(hat[0]);

Usually, instead of the above function definition, I would do void passMe(int* myArray) or void passMe(int[] myArray). But would the method above cause any issues? Knowing the answer would allow me to gain a better understanding of the things at play here, if nothing else.

Upvotes: 3

Views: 96

Answers (1)

Jeremy Friesner
Jeremy Friesner

Reputation: 73279

As far as the language-lawyers and the compiler are concerned, it's fine. The main issue will be with the human programmers (including future versions of yourself). When your standard C++ programmer sees this in a program:

void passMe(int& firstElement);  // function declaration (in a .h file)

int hat[]={ 5,2,8 };
passMe(hat[0]);

He is going to expect that passMe() might read and/or modify hat[0]. He is definitely not going to expect that passMe() might read and/or modify hat[1]. And when he eventually figures out what you are doing, he's going to be very upset with you for misleading him via unnecessarily "clever" code. :)

Furthermore, if another programmer (who doesn't know about your trick) tries to call your function from his own code, after seeing only the function declaration in the header, he's likely to try to do something like this:

int cane = 5;
passMe(cane);

... which will lead directly to mysterious undefined behavior at runtime when passMe() tries to reference the second item in the array after cane, which doesn't actually exist because cane is not actually in an array.

Upvotes: 8

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