Suppose I have the following (made up) definition:
typedef union {
struct {
unsigned int red: 3;
unsigned int grn: 3;
unsigned int blu: 2;
} bits;
uint8_t reg;
} color_t;
I know I can use this to initialize a variable that gets passed to a function, such as :
color_t white = {.red = 0x7, .grn = 0x7, .blu = 0x3};
printf("color is %x\n", white.reg);
... but in standard C, is it possible to instantiate a color_t as an immediate for passing as an argument without assigning it first to a variable?
[I discovered that yes, it's possible, so I'm answering my own question. But I cannot promise that this is portable C.]
Yes, it's possible. And the syntax more or less what you'd expect. Here's a complete example:
#include <stdio.h>
#include <stdint.h>
typedef union {
struct {
unsigned int red: 3;
unsigned int grn: 3;
unsigned int blu: 2;
} bits;
uint8_t reg;
} color_t;
int main() {
// initializing a variable
color_t white = {.bits={.red=0x7, .grn=0x7, .blu=0x3}};
printf("color1 is %x\n", white.reg);
// passing as an immediate argument
printf("color2 is %x\n", (color_t){.bits={.red=0x7, .grn=0x7, .blu=0x3}}.reg);
return 0;
}
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