Problem when assigning a pointer to an enum variable in C

Question

I am getting a warning of "assigment from incompatible pointer type". I don't understand why this warning is happening. I don't know what else to declare "the_go_status" variable to other than an integer. (Note: this is not all the code, but just a simplified version I posted to illustrate the problem.)

The warning occurs on the last line of the example I included below.

//In a header file  
enum error_type  
{  
    ERR_1 = 0,  
    ERR_2 = 1,  
    ERR_3 = 2,  
    ERR_4 = 4,  
};  


//In a header file  
struct error_struct  
{  
   int value;  
   enum error_type *status;  
};  



//In a C file  
int the_go_status;  

the_go_status = ERR_1;  

//Have the error_struct "status" point to the address of "the_go_status"  
error_struct.status = &the_go_status;    //WARNING HERE!

Solution 1

Because status is a pointer to enum error_type, and the_go_status is a pointer to an int. They are pointers to different types.

Solution 2

I'm not sure if this is related exactly to your warning or not, but be very careful assigning references to local variables to pointers within structs. If the_go_status is a local, as soon as your function returns, the reference to that local will become invalid. So, if your code (or someone else's code) uses your instance of error_struct outside the function declaring the_go_status, things will quickly break.

Solution 3

This is because enum error_type * isn't compatible with int *, because they point to values of different types (and possibly even different sizes). You should declare the_go_status as:

enum error_type the_go_status;

Although simply casting the pointer (i.e. (enum error_type *)&the_go_status) will make the warning go away, it may result in bugs on some platforms. See Is the sizeof(enum) == sizeof(int), always?

Solution 4

you should declare a pointer if you want to use a pointer:

int * the_go_status

otherwise you declare a primitive, which is not placed on the heap, but on the stack. (please correct my when being wrong on that)

However, I don't get why you want to use a pointer at all. Just do something like this in your struct definition:

enum error_type status;

and change your last line to:

error_struct.status = the_go_status; 

View more solutions