Pointer to structure member access

[Kieth89]

I thought I had this stuff down, but I was writing some code and got an error when compiling. First here is the code you need to know about:

contributions * members = new contributions[number]  //contributions is a structure;
if (members[i]->amount > 9999)

I thought that if you used new to declare a pointer to structure, you used the -> operator to access its members. But when I did that it didn't compile, so I switched it to a . operator and it works. Why? Did I misunderstand something?

Also, is this a new thing where we can't post help in title. If so, that is a good idea.

[Disch]

I thought that if you used new to declare a pointer to structure, you used the -> operator to access its members.

This is true.

The thing is, you dereference pointers only once. There are 3 different operators that dereference them:

* as in *foo
[] as in foo[0]
-> as in foo->bar

Since you are using [] to dereference your pointer, you use . instead of ->. Using both [] and -> doesn't work because then you'd be dereferencing twice.

// all the below are the same:
foo[i].bar;
(foo+i)->bar;
(*(foo+i)).bar;

[Kieth89]

ah, so if you already have any of those above (*, [], or ->) then you use '.' . Otherwise use the -> .

[Disch]

yes

[acorn]

i didnt know that. or rather, i never thought about what was happening with [] and ->.