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derverstand
Guru
Joined: 15 Dec 2005
Posts: 511
Location: /dev/null
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 Posted: Wed Aug 09, 2006 11:29 am Post subject: C: typedef struct ?? |
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Hi,
I want to setup a simple linked list in C. So I have to do something like this:
| Code: |
struct s_entry{
int value;
struct s_entry *next;
};
typedef struct entry t_entry;
... // Some Code
t_entry entry;
... // Allocation etc
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And now the big ?
Why can't I access a value like this?
It only works with
Whats the difference exaclty? And is it possible to write the "->" expression with "." ?
Best regards. |
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tboloo
Guru
Joined: 20 Jan 2006
Posts: 403
Location: Grodzisq, Poland
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| Posted: Wed Aug 09, 2006 11:50 am Post subject: |
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Hi.
Looks like you've made some mistakes - maybe you dynamically allocated memory for your struct ?If so, you'll need to dereference pointer in order to use . instead of ->, like
| Code: | | *(entry.value) = 1; |
Anyway this code below works fine
| Code: |
#include <stdio.h>
struct s_entry{
int value;
struct s_entry* next;
};
typedef struct s_entry t_entry;
int main()
{
t_entry entry;
entry.value = 1;
entry.next = NULL;
printf(" %d, %p", entry.value, entry.next );
printf("\n");
return 0;
}
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Archangel1
Veteran
Joined: 21 Apr 2004
Posts: 1212
Location: Work
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| Posted: Wed Aug 09, 2006 10:47 pm Post subject: Re: C: typedef struct ?? |
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| derverstand wrote: | | Whats the difference exaclty? And is it possible to write the "->" expression with "." ? |
Basically -> is for a pointer, . is when the variable actually is a struct. So:
| Code: |
t_entry spam;
t_entry* eggs = malloc(sizeof(t_entry));
spam.value = 5;
eggs->value = 5;
|
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What are you, stupid? |
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Voltago
Advocate
Joined: 02 Sep 2003
Posts: 2593
Location: userland
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| Posted: Wed Aug 09, 2006 10:54 pm Post subject: |
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You can even do this:
| Code: | typedef struct s_entry t_entry;
struct s_entry{
int value;
t_entry* next;
}; |
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voytas
Apprentice
Joined: 31 Mar 2004
Posts: 203
Location: Poland, Lodz
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| Posted: Thu Aug 10, 2006 9:00 am Post subject: |
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if A is a pointer to a struct these are equivalents: | Code: | (*A).val = 10;
A->val = 10; |
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tboloo
Guru
Joined: 20 Jan 2006
Posts: 403
Location: Grodzisq, Poland
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| Posted: Thu Aug 17, 2006 10:34 am Post subject: |
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| voytas wrote: | if A is a pointer to a struct these are equivalents: | Code: | (*A).val = 10;
A->val = 10; |
|
You're right. I've put right comma in a wrong place 
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