将“指针数组”传递给函数

Question

I have a top function with an array of pointers like this:

Membership *mf[5];
for(i=0;i<5;i++)
    mf[i]=(Membership*) malloc(sizeof(Membership))

where Membership is a structure. So far so good and when debugging, mf shows all the 5 entities correctly. Problem is when I pass that array of pointers to a function (which can't have anything to do with pointers) like this:

call_function(*mf)

where call_function() is declared like this:

void call_function(Membership mf[5]){
    normalize_function(mf[0],slope);
    ....
    normalize_function(mf[5],fuel);
}

In there, mf just becomes useless and with length 1 instead of 5. I can't understand what I'm doing wrong, even after searching/reading about this and debugging for a while. Please help me on how to change call_function() (not the array of pointers).

Edit: As suggested I did some changes to the code.

Edit2: In response to KyleStrand's answer: call_function() can't have anything to do with pointers because that function is actually going to be implemented in FPGA (VHDL coding) and pointers there are unecessary complications.

Answer 1

When you say that call_function "can't have anything to do with pointers", it's unclear what you mean. It appears that the function's last parameter is an array of Membership s , and in fact an array is treated very much like a pointer in C. When you pass *mf to the function, you are dereferencing the array, which is to say, you are accessing the first member of the array . This is not what you want, since call_function takes an array rather than an array member . @caveman's comment is correct: you should pass the raw array (ie without dereferencing it).

Answer 2

You seem to have some type issues. This is the sort of format you should have. It's a community wiki, so others can clean up and improve.

void call_function (Membership* local_mf[5])
{
    Membership* m = local_mf[0];
}

int main (void)
{
   Membership* mf[5];
   ... // malloc, etc, etc.
   call_function (mf);
}

Answer 3

Please clarify your question, it is unclear from your question what you would like to do.

But

Membership *mf[5] 

is a an array whose elements are pointers of type Membership

if you pass mf to a function, then you are passing an array as an argument to a function and mf itself is treated as a pointer. It points to the first element of its members. So in this case mf becomes a pointer to the first Membership pointer in its elements.

so inside the function (outside the function as well):

*mf would give you a pointer of type Membership (the first pointer)

*(mf+1) would give you a pointer of type Membersip (the second element)

**mf would give you an element of type membership (the element which the first pointer evaluates to).

you cannot get the length of mf or any array inside a function, because if you pass an array as an argument, it is treated like a pointer inside the function, so if you do something like:

sizeof(array)/sizeof(first_element) 

sizeof(array) inside the function will always equal to the size of a pointer, which will be 4 or 8 bytes depending on your system.

so if you are using sizeof(mf)/sizeof(Membership*) to get the length of mf inside your function, that just means 8/8 or 4/4 which will always equal 1.