Assign member values of struct from pointer

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.

Charlie Martin · Accepted Answer · 2012-10-23 01:30:23Z

2

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();

answered Oct 23, 2012 at 1:30

Charlie Martin

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bbg · Accepted Answer · 2012-10-23 01:31:14Z

1

The function return value is struct cal_t *, which is pointer type.

So,you should assign the return value to variable that the type is a struct cal_t *.

For example,

struct cal_t *cal_ptr;

cal_ptr = lld_tpReadCalibration();

answered Oct 23, 2012 at 1:31

bbg

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