c - Copy a structure to a member of another structure -

i'm on sdcc 3.4 , midi project musical instrument, , it's couple of days i'm struggling this... find somehow difficult explain, here try make better example. basically, scanning button presses, send midi information , lit leds accordingly. need sort of database holding data related each button, of part must constant (ids of buttons , leds) , part can variable because can varied user. @ initialization phase need assign constant part structure , leave variable part unchanged. when user modifies function of button, need overwrite variable part , leave constant part unchanged.

// structure constant part typedef struct {   unsigned char btnid; // holds n. of input pin button   unsigned char ledid; // holds n. of output pin led } sbtnconst;  // structure variable part typedef struct {   unsigned char ccnum; // holds cc number send   unsigned char ccval; // holds cc value tu send } sbtnvar;  // structure containing data typedef struct {   sbtnconst c;   sbtnvar v; } sbutton;  // declare array of button structures // these contain both constant , variable data sbutton button[4];  // initialize constant structure constant part const sbtnconst cbtndefinitions[4] = {   { 15, 0 },   { 14, 1 },   { 10, 8 },   { 12, 5 }, }; 

now, need copy whole content of cbtndefinitions[] button[]->c. if

memcpy(&button->c, &cbtndefinitions, sizeof(cbtndefinitions)); 

the data copied in c , v sequentially, not in member c.

the rest of code in main loop() goes this:

void dobutton(sbutton *btn, unsigned char value) {   litled(btn->c.ledid, !value);   sendmidicc(btn->v.ccnum, btn->v.ccval); }  // callback function called every time button has been pushed void abuttonhasbeenpushed(unsigned char id, unsigned char value) {   unsigned char i;   (i=0; i<num_of_buttons; ++i)     if (i == button[i].c.btnid)       dobutton(&button[i], value); } 

of course may have different types of buttons, can use sbutton structure other purposes, , have them processed same functions.

you need loop, source cbtndefinitions contiguous memory area whilst destination consists of 4 separate memory areas.

you can memcpy:

int i; (i = 0; < 4; ++i) {     memcpy(&button[i].c, cbtndefinitions + i, sizeof(sbtnconst)); } 

but simple assignment works gcc:

int i; (i = 0; < 4; ++i) {     button[i].c = cbtndefinitions[i]; }