HP aC++/HP C A.06.28 Programmer's Guide Integrity servers (769150-001, March 2014)

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; // Offset 0, no padding
S1 s; // Offset 1, no padding
char c2; // Offset 13, nopadding
}; // sizeof(S3)==14, alignment 1
struct S4 {
char c1; // Offset 0, no padding
S2 s; // Offset 1, no padding
char c2; // Offset 7, no padding
}; // sizeof(S4)==8, alignment 1
#pragma pack
struct S5 { // Same as S1
char c1; // Offset 0, 3 bytes padding
int i; // Offset 4, no padding
char c2; // Offset 8, 3 bytes padding
}; // sizeof(S5)==12, alignment 4
#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