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/* Packed structs */
#include <stdio.h>
#define offsetof(s,f) (int)&(((struct s *)0)->f)
/* Simple packing */
#pragma pack(1)
struct s1 { unsigned short x; int y; double z; };
void test1(void)
{
struct s1 s1;
printf("sizeof(struct s1) = %d\n", sizeof(struct s1));
printf("offsetof(x) = %d, offsetof(y) = %d, offsetof(z) = %d\n",
offsetof(s1,x), offsetof(s1,y), offsetof(s1,z));
s1.x = 123; s1.y = -456; s1.z = 3.14159;
printf("s1 = {x = %d, y = %d, z = %.5f}\n\n", s1.x, s1.y, s1.z);
}
/* Packing plus alignment */
#pragma pack(2,16)
struct s2 { unsigned char x; int y; double z; };
char filler1;
struct s2 s2;
void test2(void)
{
printf("sizeof(struct s2) = %d\n", sizeof(struct s2));
printf("&s2 mod 16 = %d\n", ((int) &s2) & 0xF);
printf("offsetof(x) = %d, offsetof(y) = %d, offsetof(z) = %d\n",
offsetof(s2,x), offsetof(s2,y), offsetof(s2,z));
s2.x = 12345; s2.y = -456; s2.z = 3.14159;
printf("s2 = {x = %d, y = %d, z = %.5f}\n\n", s2.x, s2.y, s2.z);
}
/* Now with byte-swapped fields */
#pragma pack(1,1,1)
struct s3 {
unsigned char x;
unsigned short y;
unsigned int z;
signed short v;
signed int w;
char * p;
unsigned int t[3];
unsigned char s[2];
};
struct s3 s3;
void test3(void)
{
char xx;
printf("sizeof(struct s3) = %d\n", sizeof(struct s3));
printf("offsetof(s) = %d\n", offsetof(s3,s));
s3.x = 123;
s3.y = 45678;
s3.z = 0x80000001U;
s3.v = -456;
s3.w = -1234567;
s3.p = &xx;
s3.t[0] = 111;
s3.t[1] = 222;
s3.t[2] = 333;
s3.s[0] = 'o';
s3.s[1] = 'k';
printf("s3 = {x = %u, y = %u, z = %u, v = %d, w = %d, p is %s, t = {%d,%d,%d}, s = {'%c','%c'}}\n\n",
s3.x, s3.y, s3.z, s3.v, s3.w,
(s3.p == &xx ? "ok" : "BAD"),
s3.t[0], s3.t[1], s3.t[2],
s3.s[0], s3.s[1]);
}
/* Back to normal */
#pragma pack()
struct s4 { unsigned short x; int y; double z; };
void test4(void)
{
struct s4 s4;
printf("sizeof(struct s4) = %d\n", sizeof(struct s4));
printf("offsetof(x) = %d, offsetof(y) = %d, offsetof(z) = %d\n",
offsetof(s4,x), offsetof(s4,y), offsetof(s4,z));
s4.x = 123; s4.y = -456; s4.z = 3.14159;
printf("s4 = {x = %d, y = %d, z = %.5f}\n\n", s4.x, s4.y, s4.z);
}
/* One more, with packed attribute */
struct __attribute((packed)) s5 { unsigned short x; int y; double z; };
void test5(void)
{
struct s5 s5;
printf("sizeof(struct s5) = %d\n", sizeof(struct s5));
printf("offsetof(x) = %d, offsetof(y) = %d, offsetof(z) = %d\n",
offsetof(s5,x), offsetof(s5,y), offsetof(s5,z));
s5.x = 123; s5.y = -456; s5.z = 3.14159;
printf("s5 = {x = %d, y = %d, z = %.5f}\n\n", s5.x, s5.y, s5.z);
}
/* Test harness */
int main(int argc, char ** argv)
{
test1();
test2();
test3();
test4();
test5();
return 0;
}
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