This question already has answers here:
Why should we typedef a struct so often in C?
(15 answers)
Closed 20 days ago.
I have seen this expression in the code of other developer and I cannot get the meaning of it, the code line is:
typedef struct _Space Space;
So, for the syntax I reckon that _Space is a kind of variable or something similar but I do not know what kind of variable it is (integer, string, Boolean, etc).
Anyone have any idea??
struct _Space refers to a definition of a struct _Space elsewhere. The typedef ... Space means you can refer to a struct _Space as simply Space, saving you some typing.
For example, consider the difference in brevity and clarity between
struct _Space mySpace; // Oh god! memories
vs
Space mySpace;
Related
This question already has answers here:
How to create a typedef for function pointers
(3 answers)
Closed 5 years ago.
I was going through one of the lecture slide taught in the class which included a typedef keyword in it. As opposed to normal use of typedef keyword where we usually put a alias for particular data, there was no alias put up for that example. Following is the example:See the typedef in the slide
Is the use of typedef correct, or am I interpreting differently?
It is a function pointer. And it is perfectly valid syntax.
Ptr is declared as a pointer to a function where the function takes two int arguments and return an int. Here you can use Ptr as the alias to the typedefed type.
This question already has answers here:
Is it a good idea to typedef pointers?
(15 answers)
Closed 8 years ago.
i would like to understand when creating a pointer to a struct is it necessary to declare a typedef struct declaration of this nature:
what i mean is
typedef struct _something{
int okay;
}blah;
typedef struct _something *finger;
what is the reason that it is declared in this way , why not just declare a pointer this way
blah *arm;
so if somebody can help me understand this and which is used in which case and why and its advantages?
When using typedef struct _something, it means that each time you write _something it's as if your are writing struct _something. The typedef command just tells to replace what is written. So in other words, it avoids you to write struct _something.
Hoping it helps
This question already has an answer here:
Dereferencing pointer to incomplete type
(1 answer)
Closed 9 years ago.
I have this in input_lib.c:
#include "input_lib.h"
struct edge {
int from;
int to;
};
input_lib.h contains my typedef:
typedef struct edge edge;
Then in another file which includes input_lib.h, I declare a variable and attempt to use it:
edge *my_edge = read_next_edge();
printf("%d, %d", my_edge->from, my_edge->to);
I get the error at the printf line:
error: dereferencing pointer to incomplete type
read_next_edge() returns an edge* that is allocated by:
edge *next_edge = malloc(sizeof(struct edge));
My C is a little rusty so I assume I've just made a small mistake somewhere, but I'm having a really hard time figuring out where. I would really appreciate if someone could explain where my mistake is, and why I'm getting it. Thanks
Your struct definition should be in input_lib.h
If you are expecting to access the internals of the structure outside of input_lib.c, then the structure definition needs to be in input_lib.h. If you are expecting code outside of input_lib.c to use access functions to get at the information, then you can leave the structure opaque (incomplete) but you need to call the functions to get the information.
Either way works; choose one and stick with it.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
undefined C struct forward declaration
How is it possible to declare a pointer to structure even when I do not declare a structure?
#include<stdio.h>
int main(){
struct s{
struct p *ptr;
};
}
Why does the above compile successfully?
It's possible because the compiler doesn't need to know anything about the structure if it only deals with a pointer to it.
This is a commonly used technique and is usually called an “opaque pointer”.
Look into the below link
http://cboard.cprogramming.com/cplusplus-programming/100298-opaque-pointer.html
This question already has answers here:
Closed 12 years ago.
Possible Duplicate:
What does 'unsigned temp:3' means
I don't understand this struct definition. It seems illegal to me, but apparently it isn't:
typedef struct
{
unsigned i:1;
} my_struct;
I believe that marking the variable as unsigned without a type is the same as marking it as unsigned int. However, I'm completely baffled by the colon. What does it do? My guess is that it's some sort of initializer, but I haven't a clue what it means. Off the top of my head, the only place that I'd expect a colon in C is in the ternary operator, which this obviously isn't. So, this appears to be a construct with which I am not familiar. Can anyone explain what the purpose of the colon is in this struct definition? What exactly does the declaration unsigned i:1; mean?
It defines i to be of 1 bit width.
If i:x is given then it defines i to be x bits wide.