c - Structure member declaration with " : 1 " -

i found structure in linux kernel file include/sound/soc-dapm.h . confused declaration of members.i looked on google couldn't find informative stuff. if can explain why there :1 after every variable declaration,it great help. here part of code.

struct snd_soc_dapm_widget {      unsigned int off_val;                   /* off state value */     unsigned char power:1;                  /* block power status */     unsigned char invert:1;                 /* invert power bit */     unsigned char active:1;                 /* active stream on dac, adc's */     unsigned char connected:1;              /* connected codec pin */  } 

thanks.

it's called "bit field". it's memory optimization. lets store type in less space need otherwise.

(code above link).

#include <stdio.h> #include <string.h>  struct {   unsigned int age : 3; } age;  int main( ) {    age.age = 4;    printf( "sizeof( age ) : %d\n", sizeof(age) );    printf( "age.age : %d\n", age.age );     age.age = 7;    printf( "age.age : %d\n", age.age );     age.age = 8;    printf( "age.age : %d\n", age.age );     return 0; } 

outputs:

sizeof( age ) : 4 age.age : 4 age.age : 7 age.age : 0  

notice how assigning value higher 2³ reduces size of age.age 0? because :3. means unsigned char active:1; example great storing booleans: can only true or false, can't accidentally store 255 (which happens maximum value of unsigned char).