HP C/aC++ for PA-RISC Software manual Data Alignment Pragmas

// Offset 0, no padding // Offset 1, no padding // Offset 13, nopadding

// sizeof(S3)==14, alignment 1

// Offset 0, no padding // Offset 1, no padding // Offset 7, no padding

// sizeof(S4)==8, alignment 1

// Same as S1

// Offset 0, 3 bytes padding // Offset 4, no padding

// Offset 8, 3 bytes padding // sizeof(S5)==12, alignment 4

int i;		// Offset 4, no padding
char	c2;	// Offset 8, 3 bytes padding
};		// sizeof(S1)==12, alignment 4
#pragma	pack 1
struct S2 {
char	c1;	// Offset 0, no padding
int i;		// Offset 1, no padding
char	c2;	// Offset 5, no padding
};		// sizeof(S2)==6, alignment 1

//S3 and S4 show that the pragma does not affect class fields

//unless the class itself was defined under the pragma. struct S3 {

char c1; S1 s; char c2;

};

struct S4 { char c1; S2 s; char c2;

};

#pragma pack

struct S5 { char c1; int i; char c2;

};

#pragma pack (push, my_new_align, 1)

struct S6 {		//	Same as S2
char	c1;	//	Offset 0, no padding
int i;		//	Offset 1, no padding
char	c2;	//	Offset 5, no padding
};		//	sizeof(S6)==6, alignment 1
#pragma	pack	2
#pragma	pack	show // compiler diagnostic
			// that shows current
			// pragma pack setting
struct S7 {
char	c1; // Offset 0, 1 byte padding
int i;		// Offset 2, no padding
char	c2; // Offset 6, 1 byte padding
};		//	sizeof(S7)==8, alignment 2
#pragma	pack	(pop, my_new_align)
struct S8		{	// Same as S1
char	c1;	//	Offset 0, 3 bytes padding
int i;		//	Offset 4, no padding
char	c2;	//	Offset 8, 3 bytes padding
};		//	sizeof(S8)==12, alignment 4

The pack pragma may be useful when porting code between different architectures where data type alignment and storage differences are of concern. Refer to the following examples:

Data Alignment Pragmas 99