codebackup/byte_alignment.c at master · M4cr0v/codebackup · GitHub

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/*
 * =====================================================================================
 *
 *       Filename:  byte_alignment.c
 *
 *    Description:
 *
 *        Version:  1.0
 *        Created:  2012年09月24日 10时54分12秒
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  YOUR NAME (),
 *   Organization:
 *
 * =====================================================================================
 */

#include <stdio.h>
//#pragma pack (8)

void byte_alignment_test(void)
{
	struct S12 {
		char a;
		short b;
	} s12;
	struct S124 {
		char a;
		short b;
		int c;
	} s124;
	struct S142 {
		char a;
		int b;
		short c;
	} s142;
	struct S18 {
		char a;
		double b;	/* the alignment modulus of double and long double type are 4 bytes in 32bit Linux, though they take 8 and 12 bytes respectively; in windows, modulus and space are all 8 bytes */
	} s18;
	struct S181 {
		char a;
		double b;
		char c;
	} s181;
	struct S184 {
		char a;
		double b;
		int c;
	} s184;
	struct S1824 {
		char a;
		double b;
		short c;
		int d;
	} s1824;
	struct S1_142_2 {
		char a;
		struct S142 b;
		short c;
	} s1_142_2;

	printf
	    ("Note that the alignment modulus of double and long double type are 4 bytes in 32bit Linux, though they take 8 and 12 bytes respectively; in windows, modulus and space are all 8 bytes.\n");
	printf("s12: %d + %d = %d \n", sizeof(s12.a), sizeof(s12.b),
	       sizeof(s12));
	printf("s124: %d + %d + %d = %d \n", sizeof(s124.a),
	       sizeof(s124.b), sizeof(s124.c), sizeof(s124));
	printf("s142: %d + %d + %d = %d \n", sizeof(s142.a),
	       sizeof(s142.b), sizeof(s142.c), sizeof(s142));
	printf("s18: %d + %d = %d \n", sizeof(s18.a), sizeof(s18.b),
	       sizeof(s18));
	printf("s181: %d + %d + %d = %d \n", sizeof(s181.a),
	       sizeof(s181.b), sizeof(s181.c), sizeof(s181));
	printf("s184: %d + %d + %d = %d \n", sizeof(s184.a),
	       sizeof(s184.b), sizeof(s184.c), sizeof(s184));
	printf("s1824: %d + %d + %d + %d = %d \n", sizeof(s1824.a),
	       sizeof(s1824.b), sizeof(s1824.c), sizeof(s1824.d),
	       sizeof(s1824));
	printf("s1_142_2: %d + %d + %d = %d \n", sizeof(s1_142_2.a),
	       sizeof(s1_142_2.b), sizeof(s1_142_2.c), sizeof(s1_142_2));

}