Question

I have a struct and a function, which returns a pointer to the struct it read:

typedef struct cal_t {
    float xm; 
    float ym; 
    float xn; 
    float yn; 
} cal_t;


struct cal_t *lld_tpReadCalibration(void);

Somewhere else, I do have an instance of that struct:

struct cal_t cal;

Now I need to assign tha values of that instance of the struct to the values of the struct I get the pointer returned of. So what I want is that cal.xm is the same value as cal->xm in inside lld_tpReadCalibration(). Symbolicly:

struct cal_t cal;

cal = lld_tpReadCalibration();

But this dosen’t work, of course:

error: incompatible types when assigning to type 'volatile struct cal_t' from type 'struct cal_t *'

How can I make this work the way I want it?

Thanks for your help.

Answer 1

You need to dereference the pointer somehow. You’re getting back a pointer from the function, so you’re looking for either a * operator or ->, which is of course a synonym for a * with .

You define cal as a struct cal_t, the function returns a pointer to cal_t. so you need to dereference the pointer.

cal = *lld_tpReadCalibration();