TLV可变结构体

 1 #include <stdio.h>
 2 #include <malloc.h>
 3 #include <string.h>
 4 
 5 typedef unsigned char UCHAR;
 6 typedef char CHAR;
 7 typedef unsigned long ULONG;
 8 typedef unsigned int USHORT; 
 9 #include <stdio.h>
10 #include <string.h>
11 
12 
13 
14 typedef struct STRUCT_TLV
15 {
16     USHORT usType;
17     USHORT usLen;
18     UCHAR ucValue[0];
19 }TLV;
20 
21 int main() 
22 {
23     UCHAR *pdata = NULL;
24     TLV * pstTLV = NULL;
25     const CHAR * p1 = "ab";
26     const CHAR * p2 = "cde";
27 
28     printf("sizeof(TLV)=%d", sizeof(TLV));
29 
30     pdata = (UCHAR *)malloc(2 * (sizeof(TLV) + sizeof(UCHAR)));  /*此处虽然没按照所用空间申请，但结果正确，建议不这样做*/
     if (pdata == NULL)
32     {
33         return 0;
34     }
35 
36     pstTLV = (TLV *)pdata;
37 
38     pstTLV->usType = 0x01;
39     pstTLV->usLen = strlen(p1) + 1;
40     memcpy((void *)pstTLV->ucValue, (void *)p1, pstTLV->usLen);
41     printf("\r\n TLV1:"
42            "\r\n usType=%u"
43            "\r\n usLen=%u"
44            "\r\n ucValue=%s\r\n",
45            pstTLV->usType, pstTLV->usLen, pstTLV->ucValue);
46 
47     pstTLV++;
48     pstTLV->usType = 0x02;
49     pstTLV->usLen = strlen(p2) + 1;
50     memcpy((void *)pstTLV->ucValue, (void *)p2, pstTLV->usLen);
51     
52     printf("\r\n TLV2:"
53         "\r\n usType=%u"
54         "\r\n usLen=%u"
55         "\r\n ucValue=%s\r\n",
56            pstTLV->usType, pstTLV->usLen, pstTLV->ucValue);
57 
58 
59     return 0;
60 }
61 

  pdata = (UCHAR *)malloc(2 * (sizeof(TLV) + sizeof(UCHAR)));  /*此处虽然没按照所用空间申请，但结果正确，建议不这样做*/
  虽然后面的操作越界，但结果还是对的，不知为什么。

  但最好还是按照实际所用申请。

pdata = (UCHAR *)malloc(2 * sizeof(TLV) + 3 * sizeof(UCHAR)+ 4 * sizeof(UCHAR));