[SOURCE]
...
main()
{
struct activity x[LIST_SIZE];
struct activity [LIST_SIZE] * y = &x;
FillArray((struct activity [LIST_SIZE] *)y)
....
}
FillArray(struct activity [LIST_SIZE] * x)
{
int i;
for(i = 0; i < 100; ++i)
*(x+i)->member = (WHATEVER VALUE);
}
[/SOURCE]Pointer To Array Of Structs
Author
Alright, I'm finally on C++, and I need help figuring out how to represent an array of structs using pointers. Lets say I've got a struct called activities, and I want one called x with 100 elements. How would I set up a pointer to pass this struct to a function from one it's defined in, and how would I access it then using pointers?
I've got something like this:
Anyway, with something similar to that the compiler is telling me that I can't do this:
main.cpp: In function `int FillArray(activity**)':
main.cpp:24: request for member `inode' in `*(x + (+(i * 4)))', which is of
non-aggregate type `activity*'
Please help me understand what I'm doing wrong. I'm completely lost.
Author
I've also tried another syntax...which didn't work either:
It's now giving me:
main.cpp:24: invalid type argument of `unary *'
[SOURCE]...main(){ struct activity x[LIST_SIZE]; struct activity * y = x; FillArray((struct activity *)y);}FillArray(struct activity * x){ int i; for(i = 0; i < LIST_SIZE; ++i) *(x+i)->MEMBER = SOMEVALUE....[/SOURCE]It's now giving me:
main.cpp:24: invalid type argument of `unary *'
If MEMBER is a pointer inside the struct, this should be
else you should use
The explicit cast to 'struct activity*' inside the function call isn't necessary.
*((x+i)->MEMBER) = SOMEVALUEelse you should use
(x+i)->MEMBER = SOMEVALUEThe explicit cast to 'struct activity*' inside the function call isn't necessary.
Author
Quote:Original post by Anonymous Poster
If MEMBER is a pointer inside the struct, this should be
*** Source Snippet Removed ***
else you should use
*** Source Snippet Removed ***
The explicit cast to 'struct activity*' inside the function call isn't necessary.
Okay...but shouldn't I use a dereference to access the value of the member in the struct? When I try that it says that I'm not allowed to use the * operator.
struct activity{ int ID; // or whatever;};void fill(activity *ptr,int n,int v){ for(int i=0;i<n;++i) ptr.ID=v;}int main(){ activity x[20]; fill(x,20,0);}In C++, you don't need to prefix activity with struct once it has been defined. You don't need to assign the address of x or cast it. In the example above, x is treated like a pointer to an array of structs. And if you apply [] to a pointer, it dereferences it.
Oh, and prefer vector<activity> x over an array.
[Edit] Actually, the last line about vector was a bit harsh for a local stack-based array.
[Edited by - EasilyConfused on April 25, 2006 3:23:12 AM]
Quote:Original post by BringBackFuturamaQuote:Original post by Anonymous Poster
If MEMBER is a pointer inside the struct, this should be
*** Source Snippet Removed ***
else you should use
*** Source Snippet Removed ***
The explicit cast to 'struct activity*' inside the function call isn't necessary.
Okay...but shouldn't I use a dereference to access the value of the member in the struct? When I try that it says that I'm not allowed to use the * operator.
The -> operator deferences it.
Anon Poster, it might be best you do not post when you clearly do not know what you are talking about :)
-> is not applicable and EasilyConfused is correct.
-> is not applicable and EasilyConfused is correct.
This topic is closed to new replies.
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