“Address of” (&) an array / address of being ignored be gcc?

Question

I am a teaching assistant of a introductory programming course, and some students made this type of error:

char name[20];
scanf(\"%s\",&name);
         


        

Answer 1

In your example, the array test is a block of 50 ints. So it looks like this:

| int | int | ... | int |

When you apply the unary & operator to an array, you get the address of the array. Just like when you apply it to anything else, really. So &test is a pointer that points to that block of 50 ints:

(&test) -----------> | int | int | ... | int |

A pointer that points to an array of 50 ints has type int (*)[50] - that's the type of &test.

When you just use the name test in any place where it's not the operand of either the sizeof or unary-& operators, it is evaluated to a pointer to its first element. So the test that you pass to foo() evaluates to a pointer to the test[0] element:

(test) -----------------\
                        v
(&test) -----------> | int | int | ... | int |

You can see that these both are pointing to the same address - although &test is pointing to the whole array, and test is pointing to the first element of the array (which only shows up in the different types that those values have).