How do I assign values to an array within a typdef structure in C?

Question

I am trying to assign values to an array within a typedef struct and continually am getting an syntax error.

Error expected '=', ',', ';', 'asm' or '__attribute__' before '.' token

Here is my code:

myfile.h

#define  Digit12  0x00u
#define  Digit34  0x01u
#define  Digit56  0x01u

typedef struct
{
   uint8_t trData[3]; 
} CImageVersion;

myfile.c

CImageVersion oImageVersion; // declare an instance

oImageVersion.trData = { Digit12, Digit34, Digit56};

Later on in the code

otherfile.c

extern CImageVersion oImageVersion;

An arry is a pointer but if i change the assignment to

oImageVersion->trData = { Digit12, Digit34, Digit56};

I get the same error. I am very confused as to what I am doing wrong The error is pointing to directly after the oImageVersion when I assign the values

You can't assign to an array. Only initialize it on definition or copy to it. — Some programmer dude
– Some programmer dude, Commented Oct 23, 2017 at 17:18
Try CImageVersion oImageVersion; // declare an instance oImageVersion.trData = { Digit12, Digit34, Digit56}; --> CImageVersion oImageVersion = { {Digit12, Digit34, Digit56} }; — BLUEPIXY
– BLUEPIXY, Commented Oct 23, 2017 at 17:19
Also, -> is for pointers to structures. Actual structures use . — Lee Daniel Crocker
– Lee Daniel Crocker, Commented Oct 23, 2017 at 17:38
Rather than assign the array, assign the structure: oImageVersion = (CImageVersion) { {Digit12, Digit34, Digit56} }; — chux
– chux, Commented Oct 23, 2017 at 17:41

dbush · Accepted Answer · 2017-10-23 17:21:49Z

3

You can't assign directly to an array. The syntax you're using is only valid when a variable is defined. I.e. you can do this:

CImageVersion oImageVersion = { { Digit12, Digit34, Digit56} };

But not this:

CImageVersion oImageVersion;
oImageVersion.trData = { Digit12, Digit34, Digit56};

If you don't assign the values when the variable is defined, you need to assign to each array element individually:

oImageVersion.trData[0] = Digit12;
oImageVersion.trData[1] = Digit34;
oImageVersion.trData[2] = Digit56;

answered Oct 23, 2017 at 17:21

dbush

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