Reputation: 3251
I have a struct defined as:
struct {
char name[32];
int size;
int start;
int popularity;
} stasher_file;
and an array of pointers to those structs:
struct stasher_file *files[TOTAL_STORAGE_SIZE];
In my code, I'm making a pointer to the struct and setting its members, and adding it to the array:
...
struct stasher_file *newFile;
strncpy(newFile->name, name, 32);
newFile->size = size;
newFile->start = first_free;
newFile->popularity = 0;
files[num_files] = newFile;
...
I'm getting the following error:
error: dereferencing pointer to incomplete type
whenever I try to access the members inside newFile
. What am I doing wrong?
Upvotes: 43
Views: 228436
Reputation: 83
The reason is you did not declare type struct stasher_file
, you define a struct variable stasher_file
instead.
In C
, the declaration of structure:
struct structure-tag {
member1
member2
...
};
structure-tag
is an optional name following the keyword struct
.
After declaration, you can define a variable:
struct structure-tag var1, *var2;
Also, you can do both declaration and definition like:
struct structure-tag {
member1
member2
...
} var1, *var2;
So in your case, you could try this:
struct stasher_file {
char name[32];
int size;
int start;
int popularity;
} *files[TOTAL_STORAGE_SIZE];
struct stasher_file *newFile = malloc(sizeof(struct stasher_file));
... other code ...
That's all.
Upvotes: 0
Reputation: 1696
the case above is for a new project. I hit upon this error while editing a fork of a well established library.
the typedef was included in the file I was editing but the struct wasn't.
The end result being that I was attempting to edit the struct in the wrong place.
If you run into this in a similar way look for other places where the struct is edited and try it there.
Upvotes: 5
Reputation: 90184
The reason why you're getting that error is because you've declared your struct
as:
struct {
char name[32];
int size;
int start;
int popularity;
} stasher_file;
This is not declaring a stasher_file
type. This is declaring an anonymous struct
type and is creating a global instance named stasher_file
.
What you intended was:
struct stasher_file {
char name[32];
int size;
int start;
int popularity;
};
But note that while Brian R. Bondy's response wasn't correct about your error message, he's right that you're trying to write into the struct
without having allocated space for it. If you want an array of pointers to struct stasher_file
structures, you'll need to call malloc
to allocate space for each one:
struct stasher_file *newFile = malloc(sizeof *newFile);
if (newFile == NULL) {
/* Failure handling goes here. */
}
strncpy(newFile->name, name, 32);
newFile->size = size;
...
(BTW, be careful when using strncpy
; it's not guaranteed to NUL-terminate.)
Upvotes: 1
Reputation: 347636
You are using the pointer newFile
without allocating space for it.
struct stasher_file *newFile = malloc(sizeof(stasher_file));
Also you should put the struct name at the top. Where you specified stasher_file is to create an instance of that struct.
struct stasher_file {
char name[32];
int size;
int start;
int popularity;
};
Upvotes: 13
Reputation: 31061
How did you actually define the structure? If
struct {
char name[32];
int size;
int start;
int popularity;
} stasher_file;
is to be taken as type definition, it's missing a typedef
. When written as above, you actually define a variable called stasher_file
, whose type is some anonymous struct type.
Try
typedef struct { ... } stasher_file;
(or, as already mentioned by others):
struct stasher_file { ... };
The latter actually matches your use of the type. The first form would require that you remove the struct
before variable declarations.
Upvotes: 12
Reputation: 320797
You haven't defined struct stasher_file
by your first definition. What you have defined is an nameless struct type and a variable stasher_file
of that type. Since there's no definition for such type as struct stasher_file
in your code, the compiler complains about incomplete type.
In order to define struct stasher_file
, you should have done it as follows
struct stasher_file {
char name[32];
int size;
int start;
int popularity;
};
Note where the stasher_file
name is placed in the definition.
Upvotes: 53