C语言指针操作字符数组demo

C语言指针操作字符数组demo，本意是使用指针操作source，函数调用一次取16个字节，调用两次获取到整个数据。

char source[32] = {0};
int *header = (int *)source;
int *pos = (int *)source;void print_value(int *arg0, int *arg1, int *arg2, int *arg3)
{if (  4 * (pos - header) >= 32)pos = header;*arg0 = *pos;pos++;*arg1 = *pos;pos++;*arg2 = *pos;pos++;*arg3 = *pos;pos++;printf("arg0:%x, arg1:%x, arg2:%x, arg3:%x\n", *arg0, *arg1, *arg2, *arg3);
}int main(void) {memcpy(source, "11223344112233445566778855667788", 32);printf("sourceData is:\n");for (int i = 0; i < 32; i++){printf("%x", source[i]);}printf("\n");printf("Result:\n");int arg0;int arg1;int arg2;int arg3;char data[32] = {0};for (int j = 0; j < 2; j++){print_value(&arg0, &arg1, &arg2, &arg3);}printf("print again.\n");for (int j = 0; j < 2; j++){print_value(&arg0, &arg1, &arg2, &arg3);}
}

运行结果：

$ ./test
sourceData is:
3131323233333434313132323333343435353636373738383535363637373838
Result:
arg0:32323131, arg1:34343333, arg2:32323131, arg3:34343333
arg0:36363535, arg1:38383737, arg2:36363535, arg3:38383737
print again.
arg0:32323131, arg1:34343333, arg2:32323131, arg3:34343333
arg0:36363535, arg1:38383737, arg2:36363535, arg3:38383737
$

===================================================
下面是稍微变化点的操作，
需求是这样的：操作RPMB的data_frame长度是512字节，写入数据时需要计算数据的hmac，但是计算hmac是从data_frame结构体去掉stuff和keymac后数据。

RPMB data_frame的结构体定义如下：

#define RPMB_SZ_STUFF          196
#define RPMB_SZ_MAC           32
#define RPMB_SZ_DATA          256
#define RPMB_SZ_NONCE         16
#define RPMB_SZ_COUNTER       4
#define RPMB_SZ_ADDRESS       2
#define RPMB_SZ_BLK_COUNT     2
#define RPMB_SZ_RESULT        2
#define RPMB_SZ_REQ_RESP      2
#define RPMB_SZ_RESERVED      4#define HMAC_DATALEN
#define HMAC_COUNT(x) (x + 1)typedef struct {char Stuff[RPMB_SZ_STUFF];char KeyMac[RPMB_SZ_MAC];char Data[RPMB_SZ_DATA];char Nonce[RPMB_SZ_NONCE];               //16byteschar WriteCounter[RPMB_SZ_COUNTER];      //4byteschar Address[RPMB_SZ_ADDRESS];           //2byteschar BlockCount[RPMB_SZ_BLK_COUNT];      //2byteschar Result[RPMB_SZ_RESULT];             //2byteschar RequestResponse[RPMB_SZ_REQ_RESP];  //2bytes
} RpmbDataFrame;

为了便于跨模块调用，这里重新定义了一个新的结构体，去掉了Stuff和KeyMac字段，如下：

typedef struct {                                //total 288byte = 16 * 18char Hmac_Data[RPMB_SZ_DATA];                 //256 byteschar Hmac_Nonce[RPMB_SZ_NONCE];               //16  byteschar Hmac_WriteCounter[RPMB_SZ_COUNTER];      //4   byteschar Hmac_Address[RPMB_SZ_ADDRESS];           //2   byteschar Hmac_BlockCount[RPMB_SZ_BLK_COUNT];      //2   byteschar Hmac_Result[RPMB_SZ_RESULT];             //2   byteschar Hmac_RequestResponse[RPMB_SZ_REQ_RESP];  //2   byteschar Hmac_Reserved[RPMB_SZ_RESERVED];         //4   bytes
} HmacRpmbDataFrame;

下面开始构建测试的数据，传输时可能会用到这些字段

 RpmbDataFrame dataFrame;memset(&dataFrame, 0, sizeof(RpmbDataFrame));//init datamemcpy(dataFrame.Stuff, "aaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaa", 196);memcpy(dataFrame.KeyMac, "hhiijjkkhhiijjkkhhiijjkkhhiijjkk", 32);memcpy(dataFrame.Data, "1111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444", 256);memcpy(dataFrame.WriteCounter, "1234", RPMB_SZ_COUNTER); //4 bytesmemcpy(dataFrame.Address, "12", RPMB_SZ_COUNTER);        //2 bytememcpy(dataFrame.BlockCount, "34", RPMB_SZ_BLK_COUNT);   //2 bytesmemcpy(dataFrame.RequestResponse, "56", RPMB_SZ_REQ_RESP); //2 bytes

然后我们把这些初始的数据，拷贝到另一个待运算的结构体中

 //copy data to HmacRpmbDataFrame structHmacRpmbDataFrame hmacRpmbData;memset(&hmacRpmbData, 0, sizeof(HmacRpmbDataFrame));memcpy(hmacRpmbData.Hmac_Data, dataFrame.Data, RPMB_SZ_DATA);memcpy(hmacRpmbData.Hmac_Nonce, dataFrame.Nonce, RPMB_SZ_NONCE);memcpy(hmacRpmbData.Hmac_WriteCounter, dataFrame.WriteCounter, RPMB_SZ_COUNTER);memcpy(hmacRpmbData.Hmac_Address, dataFrame.Address, RPMB_SZ_ADDRESS);memcpy(hmacRpmbData.Hmac_BlockCount, dataFrame.BlockCount, RPMB_SZ_BLK_COUNT);memcpy(hmacRpmbData.Hmac_Result, dataFrame.Result, RPMB_SZ_RESULT);memcpy(hmacRpmbData.Hmac_RequestResponse, dataFrame.RequestResponse, RPMB_SZ_REQ_RESP);

接下来的跨模块传输需求是一次只能发送16个字节，函数有四个参数，每个参数4个字节。

 int *RotInfoPoint = (int *)&hmacRpmbData;int *RotInfoPointHeader = (int *)&hmacRpmbData;int arg0, arg1, arg2, arg3;for (int i = 0; i < 18; i++) //284 bytes ,18*16 = 288{arg0 = *RotInfoPoint;RotInfoPoint++;arg1 = *RotInfoPoint;RotInfoPoint++;arg2 = *RotInfoPoint;RotInfoPoint++;arg3 = *RotInfoPoint;RotInfoPoint++;printf("[%d] arg0:0x%x, arg1:0x%x, arg2:0x%x, arg3:0x%x\n",i+1, arg0,arg1,arg2,arg3);}//reset point to header positionRotInfoPoint = RotInfoPointHeader;

完整demo Code：

#define RPMB_SZ_STUFF          196
#define RPMB_SZ_MAC           32
#define RPMB_SZ_DATA          256
#define RPMB_SZ_NONCE         16
#define RPMB_SZ_COUNTER       4
#define RPMB_SZ_ADDRESS       2
#define RPMB_SZ_BLK_COUNT     2
#define RPMB_SZ_RESULT        2
#define RPMB_SZ_REQ_RESP      2
#define RPMB_SZ_RESERVED      4#define HMAC_DATALEN
#define HMAC_COUNT(x) (x + 1)typedef struct {char Stuff[RPMB_SZ_STUFF];char KeyMac[RPMB_SZ_MAC];char Data[RPMB_SZ_DATA];char Nonce[RPMB_SZ_NONCE];               //16byteschar WriteCounter[RPMB_SZ_COUNTER];      //4byteschar Address[RPMB_SZ_ADDRESS];           //2byteschar BlockCount[RPMB_SZ_BLK_COUNT];      //2byteschar Result[RPMB_SZ_RESULT];             //2byteschar RequestResponse[RPMB_SZ_REQ_RESP];  //2bytes
} RpmbDataFrame;typedef struct {                                //total 288byte = 16 * 18char Hmac_Data[RPMB_SZ_DATA];                 //256 byteschar Hmac_Nonce[RPMB_SZ_NONCE];               //16  byteschar Hmac_WriteCounter[RPMB_SZ_COUNTER];      //4   byteschar Hmac_Address[RPMB_SZ_ADDRESS];           //2   byteschar Hmac_BlockCount[RPMB_SZ_BLK_COUNT];      //2   byteschar Hmac_Result[RPMB_SZ_RESULT];             //2   byteschar Hmac_RequestResponse[RPMB_SZ_REQ_RESP];  //2   byteschar Hmac_Reserved[RPMB_SZ_RESERVED];         //4   bytes
} HmacRpmbDataFrame;int main(void) {printf("test hmac\n");RpmbDataFrame dataFrame;memset(&dataFrame, 0, sizeof(RpmbDataFrame));//init datamemcpy(dataFrame.Stuff, "aaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaabbbbccccddddaaaa", 196);memcpy(dataFrame.KeyMac, "hhiijjkkhhiijjkkhhiijjkkhhiijjkk", 32);memcpy(dataFrame.Data, "1111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444111122223333444411112222333344441111222233334444", 256);memcpy(dataFrame.WriteCounter, "1234", RPMB_SZ_COUNTER); //4 bytesmemcpy(dataFrame.Address, "12", RPMB_SZ_COUNTER);        //2 bytememcpy(dataFrame.BlockCount, "34", RPMB_SZ_BLK_COUNT);   //2 bytesmemcpy(dataFrame.RequestResponse, "56", RPMB_SZ_REQ_RESP); //2 bytes//copy data to HmacRpmbDataFrame structHmacRpmbDataFrame hmacRpmbData;memset(&hmacRpmbData, 0, sizeof(HmacRpmbDataFrame));memcpy(hmacRpmbData.Hmac_Data, dataFrame.Data, RPMB_SZ_DATA);memcpy(hmacRpmbData.Hmac_Nonce, dataFrame.Nonce, RPMB_SZ_NONCE);memcpy(hmacRpmbData.Hmac_WriteCounter, dataFrame.WriteCounter, RPMB_SZ_COUNTER);memcpy(hmacRpmbData.Hmac_Address, dataFrame.Address, RPMB_SZ_ADDRESS);memcpy(hmacRpmbData.Hmac_BlockCount, dataFrame.BlockCount, RPMB_SZ_BLK_COUNT);memcpy(hmacRpmbData.Hmac_Result, dataFrame.Result, RPMB_SZ_RESULT);memcpy(hmacRpmbData.Hmac_RequestResponse, dataFrame.RequestResponse, RPMB_SZ_REQ_RESP);int *RotInfoPoint = (int *)&hmacRpmbData;int *RotInfoPointHeader = (int *)&hmacRpmbData;int arg0, arg1, arg2, arg3;for (int i = 0; i < 18; i++) //284 bytes ,18*16 = 288{arg0 = *RotInfoPoint;RotInfoPoint++;arg1 = *RotInfoPoint;RotInfoPoint++;arg2 = *RotInfoPoint;RotInfoPoint++;arg3 = *RotInfoPoint;RotInfoPoint++;printf("[%d] arg0:0x%x, arg1:0x%x, arg2:0x%x, arg3:0x%x\n",i+1, arg0,arg1,arg2,arg3);}//reset point to header positionRotInfoPoint = RotInfoPointHeader;printf("test hmac done.\n");
}

运行结果：

$ ./test
test hmac
[1] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[2] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[3] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[4] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[5] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[6] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[7] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[8] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[9] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[10] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[11] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[12] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[13] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[14] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[15] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[16] arg0:0x31313131, arg1:0x32323232, arg2:0x33333333, arg3:0x34343434
[17] arg0:0x0, arg1:0x0, arg2:0x0, arg3:0x0
[18] arg0:0x34333231, arg1:0x34333231, arg2:0x36350000, arg3:0x0
test hmac done.
$

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