c - How to fill bitfields with 0xff -

is there way initialize unsigned field in bitfield 0xfff...(according its' size ofcourse) ? if use -1 warning assigning signed unsigned variable.

one solution manually create init values in enum , use them:

enum init_bit {   // etc   i_3 = 7u, // use longer names because global space   i_4 = 15u,   i_5 = 31u,   // etc }; 

you write once , becomes easy:

x x = {/*other fields*/, i_4, /*other fields*/}; 

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another solution found init 0 , decrement. defined because dealing unsigned type. if need initialize can create function this:

x get_x() {   x x;   x.a = 0;   --x.a;    return x; } 

with optimizations enable compiler direct initialize:

get_x:         movl    $15, %eax         ret 

you can use function initialization:

x x = get_x(); 

of course has disadvantage need init other fields of x in get_x.

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where x defined as:

struct x {   unsigned : 4; };  typedef struct x x; 

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it seems tricky initialize bit fields without warnings (gcc 6.1):

x x = {-1}; //!!warning: negative integer implicitly converted unsigned type [-wsign-conversion]  x x = {-1u}; //!!warning: large integer implicitly truncated unsigned type [-woverflow]  x x = {(unsigned)-1}; //!!warning: large integer implicitly truncated unsigned type [-woverflow]  x x = {~0}; //!!warning: negative integer implicitly converted unsigned type [-wsign-conversion]  x x = {~0u}; //!!warning: large integer implicitly truncated unsigned type [-woverflow]