Thread: struct member assignment (c-only)

Shift those declarations to before the other statements:

Code:

int main(void) {
	touch_switch_t S[8];
	int a=0,b=0,c=0,d=0,e=0,f=0,g=0,h=0;

	S[0].p_loc = 0x0;
	S[1].p_loc = 0x1;
	S[2].p_loc = 0x4;
	S[3].p_loc = 0x5;
	S[4].p_loc = 0x2;
	S[5].p_loc = 0x3;
	S[6].p_loc = 0x8;
	S[7].p_loc = 0x9;
	touch_switches_set(&S);
	return 0;
}

The reason you get an error on the int a ... is that you are not defining your variables before the start of code. In C++ you can literally put a variable definition anywhere any statement can go. Some C compilers allow this too, but far from all. So as soon as you start writing code statements (anything that isn't a type, function or variable declaration/definition), you can not declare any further variables in that block.

Your function prototype is also missing a () set.

The following code is compiling correctly on my machine with gcc -Wall -ansi -pedantic:

Code:

typedef struct touch_switch {
	int p_loc;
} touch_switch_t;

void touch_switches_set(touch_switch_t (*switches)[]);


int main(void) {
	touch_switch_t S[8];
	int a=0,b=0,c=0,d=0,e=0,f=0,g=0,h=0;

	S[0].p_loc = 0x0;
	S[1].p_loc = 0x1;
	S[2].p_loc = 0x4;
	S[3].p_loc = 0x5;
	S[4].p_loc = 0x2;
	S[5].p_loc = 0x3;
	S[6].p_loc = 0x8;
	S[7].p_loc = 0x9;
	touch_switches_set(&S);

	return 0;
}

void touch_switches_set(touch_switch_t (*switches)[]) {
	(*switches)[0].p_loc = 0x0;
	(*switches)[1].p_loc = 0x1;
	(*switches)[2].p_loc = 0x4;
	(*switches)[3].p_loc = 0x5;
	(*switches)[4].p_loc = 0x2;
	(*switches)[5].p_loc = 0x3;
	(*switches)[6].p_loc = 0x8;
	(*switches)[7].p_loc = 0x9;
}

--
Mats

Originally Posted by emorrp1

Thank you all very much, this solution works. I've not come across the "define all variables at the start" rule before, and also thanks for solving a mysterious "suspicious pointer conversion" compiler warning, that I had no idea what to do with, but wasn't critical.

It wasn't "critical" becaue you were lucky that the start of the array and the address of the first element are the same thing - if you had wanted to do a slightly different variant, then it would quite possibly have been critical.

--
Mats

I may be missing something, but it seems you could simply define the function like so:

Code:

void touch_switches_set(touch_switch_t *switches) {
	switches[0].p_loc = 0x0;
	switches[1].p_loc = 0x1;
	switches[2].p_loc = 0x4;
	switches[3].p_loc = 0x5;
	switches[4].p_loc = 0x2;
	switches[5].p_loc = 0x3;
	switches[6].p_loc = 0x8;
	switches[7].p_loc = 0x9;
}

Originally Posted by emorrp1

you're almost right! I tried it, but since you're now dealing with the pointer directly rather than its dereferenced state, you need to also change the '.' to '->'

No, that's incorrect. The index operator [] dereferences the pointer.
void* p;
*p and p[0] are the same thing.
So (*p).something and p[0].something are also the same thing.