C語言—用結構體指針給數組指派（結構體指針指向字元串，給字元串指派）

數組定義：

char acBuf[sizeof(TRANS_HEAD_S) + sizeof(USER_HEAD_S) + 4] = {0};
           

結構體定義：              

typedef struct 
{
	int iOne;
	int iTwo;
	int iThr;
}TRANS_HEAD_S;

typedef struct 
{
	int iUser;
}USER_HEAD_S;
           

1、實作結果：

acBuf[0] = 11
acBuf[1] = 0
acBuf[2] = 0
acBuf[3] = 0
acBuf[4] = 12
acBuf[5] = 0
acBuf[6] = 0
acBuf[7] = 0
acBuf[8] = 13
acBuf[9] = 0
acBuf[10] = 0
acBuf[11] = 0
acBuf[12] = 14
acBuf[13] = 0
acBuf[14] = 0
acBuf[15] = 0
acBuf[16] = 15
acBuf[17] = 0
acBuf[18] = 0
acBuf[19] = 0
           

2、代碼實作：

#include <stdio.h>

typedef struct 
{
	int iOne;
	int iTwo;
	int iThr;
}TRANS_HEAD_S;

typedef struct 
{
	int iUser;
}USER_HEAD_S;

int main()
{
	char acBuf[sizeof(TRANS_HEAD_S) + sizeof(USER_HEAD_S) + 4] = {0};
	TRANS_HEAD_S *pstTransHead = NULL;
	USER_HEAD_S *pstUserHead = NULL;
	int i=0;	
	int *pValue = NULL;
    
    /*pstTransHead指針指向了acBuf的頭*/
	pstTransHead = (TRANS_HEAD_S *)acBuf;

	pstTransHead->iOne = 11;
	pstTransHead->iTwo = 12;
	pstTransHead->iThr = 13;

    /*pstUserHead指向了acBuf的第13個位元組的頭，因為結構體TRANS_HEAD_S是12位元組*/
	pstUserHead = (USER_HEAD_S *)&pstTransHead[1];
	
	pstUserHead->iUser = 14;

   /*pValue指向了acBuf的第17個位元組的頭，因為結構體TRANS_HEAD_S是12位元組，USER_HEAD_S是4個位元組*/
	pValue = (int *)&pstUserHead[1];

	(*pValue) = 15;

	for(i = 0; i < sizeof(acBuf); i++)
	{
		printf("acBuf[%d] = %d\n", i, acBuf[i]);
	}
	
	return 0;
}
           

3、對代碼【pstUserHead = (USER_HEAD_S *)&pstTransHead[1];】

     的解釋——結構體指派給另一個結構體

#include <stdio.h>

typedef struct
{
	int iA;
	int iB;
	int iC;
}TEST_S;

int main(void)
{
	TEST_S t1,t2;

    /*給t1結構體指派*/	
	t1.iA = 11;
	t1.iB = 12;
	t1.iC = 13;

    /*t1結構體指派給t2結構體*/
	t2 = t1;

	printf("t2.iA=%d t2.iB=%d t2.iC=%d\n", t2.iA, t2.iB, t2.iC);
	return 0;
}
           

 結果顯示：t2.iA=11 t2.iB=12 t2.iC=13

4、char類型指針指向int類型數值,取值結果顯示

#include <stdio.h>

int main()
{
	int i = 1561;
	char c = 0;
	
	c = (char)i;
	
	printf("i=%d c=%hhu\n", i, c);
	return 0;
}
           

結果顯示是：i=1561 c=25

1561：是

25：是