C: Errors for Incompatible Types

[ekay1]

I am writing a program in C. The following is an extract from my code:

enum coin_types
{
    FIVE_CENTS=5,
    TEN_CENTS=10,
    TWENTY_CENTS=20,
    FIFTY_CENTS=50,
    ONE_DOLLAR=100,
    TWO_DOLLARS=200
};

struct coin
{
    enum coin_types denomination;
    unsigned count;
};


void * safe_malloc(size_t size)
{
    void * mem = malloc(size);
    if(!mem)
    {
        perror("Failed to allocate memory");
        abort();
    }
    return mem;
}



FILE * coinsf = NULL;
   char line[600];


   coinsf = fopen(coinsfile, "r");
   
   /* Read in each line, while line is not null */
   while(fgets(line, 600, coinsf) != NULL)
    {
       struct coin * new;


          line[strlen(line)-1] = 0;
      
       new = new_coins_data_line(line);
        }


/* this function is in another file */
struct coin new_coins_data_line(char * line)
{


   struct coin * newdata = NULL;
   newdata = (struct coin *)
      safe_malloc(sizeof(struct coin));
   
   return newdata;
   
}

I'm getting the following errors:
For: new = new_coins_data_line(line);
"Incompatible types in assignment"

For: return newdata;
"Incompatible types in return"

There seem to be problems with my variables and perhaps it is related to the type 'struct coin' which has an enumerated type within it.

Please help me fix these errors. Thank you.

[stahta01]

"struct coin" and "struct coin *" are two different types. Decide if you are returning a struct or a pointer to a struct.

struct coin new_coins_data_line(char * line)

Tim S.

[SirPrattlepod]

Additionally, you're not closing coinsf (or even checking that is was opened for that matter).

As an aside, and not that it matters, let's also look at these lines (even though they're not the source of any error -- at the moment):

char line[600];
//...
while(fgets(line, 600, coinsf) != NULL)
//...

I don't particularly like that 600. You could do something like #define MAXLINELEN 600 and use that in both your array declaration and in the fgets, but is there something better you could replace the 600 in the fgets with?

As food for thought, consider what the value of foo might be after the following line is executed:

size_t foo = sizeof line;

and also

size_t foo = sizeof line / sizeof line[0];

If you change the "element type" of line to, say, int line[600], what are the values of foo then?

[ekay1]

"struct coin" and "struct coin *" are two different types. Decide if you are returning a struct or a pointer to a struct.

struct coin new_coins_data_line(char * line)

Tim S.

Thanks, I had completely overlooked the * in the function.
I have changed it to:
struct coin * new_coins_data_line(char * line)
and that error is gone now.

I still have an error for:
new = new_coins_data_line(line);
saying "incompatible types in assignment"

[stahta01]

Do you know what a function prototype is?
If yes, use one or correct the one you are using.

// Function Prototype must be before first use of function in the file.
struct coin * new_coins_data_line(char * line);

[ekay1]

Do you know what a function prototype is?
If yes, use one or correct the one you are using.

// Function Prototype must be before first use of function in the file.
struct coin * new_coins_data_line(char * line);

This fixed it! Thank you!