Question

I have a structure as:

//GUID structure
typedef struct {
    var8 octet[16];
} GPTGUID_t;

And a long #define as:

#define PTYPE_MRP_UPPER     0x4db80b5ce3c9e316ULL
#define PTYPE_MRP_LOWER     0xae1502f02df97d81ULL

I wish to copy UPPER part in octet 0 to 7 and LOWER in 8 to 15.
Unfortunately all attempts including memcpy has failed and given segfault.

I tried something as:

        strcpy(guid.octet[0], PTYPE_MRP_UPPER);
        strcpy(guid.octet[8], PTYPE_MRP_LOWER);

And also,

memcpy(guid.octet[0], PTYPE_MRP_UPPER, sizeof(PTYPE_MRP_UPPER));
memcpy(guid.octet[8], PTYPE_MRP_LOWER, sizeof(PTYPE_MRP_LOWER));

Both have failed.

Just as a side note:

typedef unsigned char       var8;
typedef unsigned short      var16;
typedef unsigned int        var32;

However, I am able to extract the individual octets as:

    memcpy( guid.octet, pHdr->partTypeGUID, sizeof(GPTGUID_t));//copy the partitionTypeGUID
    p1 = getvar64(guid.octet[0]);
    p2 = getvar64(guid.octet[8]);

where, #define getvar64(x) (*(var64*)(&x))

Answer 1

The value 0x4db80b5ce3c9e316ULL is not a string, so strcpy treats is as a pointer and with a value like that it’s pointing way wrong.

You also can’t use strcpy as it copies until it finds a zero byte (the character '\0'). Use memcpy instead.

You also doesn’t pass pointers to the memcpy function, but values. You should turn on more warnings because the compiler will not like it, but not enough to make it an error apparently.

Try to call memcpy like this:

unsigned long long val;

val = PTYPE_MRP_UPPER;
memcpy(&guid.octet[0], &val, sizeof(val));
val = PTYPE_MRP_LOWER;
memcpy(&guid.octet[8], &val, sizeof(val));