C conditional operator in GCC -

from "21st century c" example 10.8

typedef struct { double width, height; } size_s;  size_s width_height(char *papertype){ return !strcasecmp(papertype, "a4")     ? (size_s) {.width=210, .height=297} : !strcasecmp(papertype, "letter") ? (size_s) {.width=216, .height=279} : !strcasecmp(papertype, "legal")  ? (size_s) {.width=216, .height=356}                                  : (size_s) {.width=nan, .height=nan}; } 

trying use style in winavr gcc

    (a_t_g.value.ax > xx) ?      { leds |= rpr;                  //roll positive red        leds &= ~rpa;                 //clear amber      flag |= flagrdd;                   //set flag red } : (a_t_g.value.ax < -xx) ? { leds  |= rnr;                 //roll negative red   leds &= ~rna;                 //clear amber   flag |= flagrdd;                  //set flag red } :{} 

this results in error: expected expression before '{' token.

can gcc not handle or doing wrong? how 1 handle final nothing in style?

the ternary ?: operator use in expressions. both branches need expression value; doesn't make sense have empty block. note using compound blocks in expressions gcc extension, 1 there's no reason using here.

the way work use plain if , else.

if (a_t_g.value.ax > xx) {     leds |= rpr;                  //roll positive red      leds &= ~rpa;                 //clear amber     flag |= flagrdd;              //set flag red } else if (a_t_g.value.ax < -xx) {     leds  |= rnr;                 //roll negative red     leds &= ~rna;                 //clear amber     flag |= flagrdd;              //set flag red }