数组定义：
char acBuf[sizeof(TRANS_HEAD_S) + sizeof(USER_HEAD_S) + 4] = {0};
结构体定义：
typedef struct {int iOne;int iTwo;int iThr;}TRANS_HEAD_S;typedef struct {int iUser;}USER_HEAD_S;
1、实现结果：
acBuf[0] = 11acBuf[1] = 0acBuf[2] = 0acBuf[3] = 0acBuf[4] = 12acBuf[5] = 0acBuf[6] = 0acBuf[7] = 0acBuf[8] = 13acBuf[9] = 0acBuf[10] = 0acBuf[11] = 0acBuf[12] = 14acBuf[13] = 0acBuf[14] = 0acBuf[15] = 0acBuf[16] = 15acBuf[17] = 0acBuf[18] = 0acBuf[19] = 0
2、代码实现：
#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指针指向了acBuf的头*/pstTransHead = (TRANS_HEAD_S *)acBuf;pstTransHead->iOne = 11;pstTransHead->iTwo = 12;pstTransHead->iThr = 13;/*pstUserHead指向了acBuf的第13个字节的头，因为结构体TRANS_HEAD_S是12字节*/pstUserHead = (USER_HEAD_S *)&pstTransHead[1];pstUserHead->iUser = 14;/*pValue指向了acBuf的第17个字节的头，因为结构体TRANS_HEAD_S是12字节，USER_HEAD_S是4个字节*/pValue = (int *)&pstUserHead[1];(*pValue) = 15;for(i = 0; i < sizeof(acBuf); i++){printf("acBuf[%d] = %d\n", i, acBuf[i]);}return 0;}
3、对代码【pstUserHead = (USER_HEAD_S *)&pstTransHead[1];】
的解释——结构体赋值给另一个结构体
#include <stdio.h>typedef struct{int iA;int iB;int iC;}TEST_S;int main(void){TEST_S t1,t2;/*给t1结构体赋值*/t1.iA = 11;t1.iB = 12;t1.iC = 13;/*t1结构体赋值给t2结构体*/t2 = t1;printf("t2.iA=%d t2.iB=%d t2.iC=%d\n", t2.iA, t2.iB, t2.iC);return 0;}
结果显示：t2.iA=11 t2.iB=12 t2.iC=13
4、char类型指针指向int类型数值,取值结果显示
#include <stdio.h>int main(){int i = 1561;char c = 0;c = (char)i;printf("i=%d c=%hhu\n", i, c);return 0;}
结果显示是：i=1561 c=25
1561：是
25：是
