When i try to compile the following code, i get the error
test.c: In function 'main':
test.c:16: error: incompatible types in assignment
and the code is..
#include <stdio.h>
#include <ctype.h>
#include <string.h>
typedef struct {
char name[20];
struct planet* next;
} planet;
int main(int argc, char *argv[])
{
planet *p, *start, *first, *second, *third;
strcpy(start->name, "Suthan");
start->next = *first;
}
1) Allocate some memory to your pointers.
planet *start, *first; these are uninitialized pointers.
start->next // that's dereferencing an uninitialized pointer.
2) You're setting start->next (a pointer to a planet) to a deferenced pointer first. That's the root of your error.
start->next = *first; // should be = first;
3) Move the typedef name to get rid of the warning you were seeing.
typedef struct planet{
char name[20];
struct planet* next;
};
Since are trying to assign an instance of planet (*first) to a pointer to planet (start->next).
Try this instead:
start->next = first;
However, I'm also wondering about your declaration of planet. Does this help?
typedef struct _planet {
char name[20];
struct _planet* next;
} planet;
typedef struct to typedef struct planetI think you did your struct incorrectly
typedef struct _planet {
char name[20];
struct _planet* next;
} planet;
Should be:
typedef struct planet {
char name[20];
struct planet* next;
}
I remember tripping over this aspect of self-referential structs.
typedef struct {
char name[20];
struct planet* next; /* <-- the trouble is here */
} planet;
In the middle of the struct definition, which is in the middle of a typedef definition, the compiler doesn't know what a struct planet looks like, but is happy to let you define a pointer to it. The compiler doesn't really need to know what it looks like until you dereference *next. By the time you get to the body of main() you still haven't told the compiler what a struct planet is, only a type called planet which happens to be an unnamed struct.
Consider the following approach.
struct foo {
int bar;
};
typedef struct foo foo_type;
struct foo bar;
foo_type baz;
This shows that the name of the struct is foo and the name of the defined type is foo_type. I could combine them like this:
typedef struct foo {
int bar;
} foo_type;
You can resolve the compiler warning by adding a dummy name to your inline struct definition.
typedef struct planet_struct {
char name[20];
struct planet_struct* next;
} planet;
You will also need to address the memory allocation issue that others have pointed out, but this answers the question you didn't actually ask.
start->next = first;,*firstis the struct, you need the pointer.