Pass by reference and pointers

This question already has an answer here:

What's the difference between passing by reference vs. passing by value? 18 answers

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There is no pass by reference in C, it's always pass by value.

C developers can emulate pass by reference, by passing the pointers to a variable and the accessing it using dereferencing within the function. Something like the following, which sets a variable to 42 :

static void changeTo42 (int *pXyzzy) {
    *pXyzzy = 42;
}
:
int x = 0;
changeTo42 (&x);

Contrast that with the C++ true pass by reference, where you don't have to muck about with pointers (and especially pointers to pointers, where even seasoned coders may still occasionally curse and gnash their teeth):

static void changeTo42 (int &xyzzy) {
    xyzzy = 42;
}
:
int x = 0;
changeTo42 (x);

I would implore ISO to consider adding true references to the next C standard. Not necessarily the full capability found in C++, just something that would fix all the problems people have when calling functions.

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You might be thinking of C++. I'll cover that below.

In C there is no passing by reference. To accomplish the same feat, you can send a pointer to a variable as an argument and dereference the pointer in the method, as shown in paxdiablo's comment.

In C++, you could accomplish the same thing if you tried to pass by reference C-style (as explained previously) or if you tried passing the arguments as such:

static void multiply(int& x){
    x * 7;
}

void main(){
    int x = 4;
    multiply(x);
}

The variable x at the end of this program would equal 28.

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