Storage of Bit Fields

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ANSI 3.5.2.1** The order of allocation of bit fields within an int

Bit fields are allocated within an integer from least-significant to most-significant bit. In the following code

struct mybitfields  
{  
   unsigned a : 4;  
   unsigned b : 5;  
   unsigned c : 7;  
} test;  
  
int main( void )  
{  
   test.a = 2;  
   test.b = 31;  
   test.c = 0;  
}  

the bits would be arranged as follows:

00000001 11110010  
cccccccb bbbbaaaa  

Since the 80x86 processors store the low byte of integer values before the high byte, the integer 0x01F2 above would be stored in physical memory as 0xF2 followed by 0x01.

Structures, Unions, Enumerations, and Bit Fields