Bit-fields at two separate locations in a Structure in C -

in structure have contiguous bit-fields; is, 1 after other , adjacent each other — example:

struct demo {   char a;   char b:1;   char c:2;   char d:2;   int  e;   } demo1; 

the size of demo1 8 bytes:

• size = a(1 byte) + bit-fields(1 byte) + gap(2 bytes) + e(4 bytes))

now consider following structure:

struct demo {   char a;   int  b:1;   char c;   char d;   int  e:2; } demo1; 

when use sizeof(demo1), gives me 8 bytes — want know how these bit-fields presented in memory.

if calculated above structure size should be:

• size = a(1 byte) + b(4 bytes) + c(1 byte) + d(1 byte) + e(4 bytes)

during programming don't bother thing how size calculated using sizeof , don't use bit-fields @ 2 different locations, type of question asked interviewers.

consecutive (non-zero width) bit-fields can merged single memory location, while bit-field followed non-bit-field distinct memory locations.

 struct demo  {       char a;       int b:1;       char c;       char d;       int  e:2;  } demo1; 

so in struct, there 1 non bit-field , 1 bit-field , 2 non bit-fields , bit-field.

having non-bit-field (or zero-length bit-field) right after bit-field member, follows next different/independent memory location/object.

and also:

a compiler not reorder elements of struct, because violate c standard. section 6.7.2.1 of c99 standard states:

within structure object, non-bit-field members , units in bit-fields reside have addresses increase in order in declared.