CODEWITHSUNDEEP
c++
A191919
A191919

Reputation: 3462

C++ memcpy Access violation big chunk of memory

I am new in c++ area. On line memcpy(combined + 14 + 40, pThirdPart, size); it's throws

Exception thrown at 0x0FB046EE (vcruntime140d.dll) in Memcpy.exe: 0xC0000005: Access violation reading location 0x00544000.

Why it's happening?

const long size = 8294400;
char firstPart[14] = "3412345";
char secondPart[40] = "daffda";
char *thirdPart = new char[size];

sprintf_s(thirdPart, size, "Test TEst tset ... and other symbols");

BYTE *pFirstPart = reinterpret_cast<BYTE*>(&firstPart);
BYTE *pSecondPart = reinterpret_cast<BYTE*>(&secondPart);
BYTE *pThirdPart = reinterpret_cast<BYTE*>(&thirdPart);

BYTE *combined = new BYTE[(size + 14 + 40)];

memcpy(combined, pFirstPart, 14);
memcpy(combined + 14, pSecondPart, 40);
memcpy(combined + 14 + 40, pThirdPart, size);

Upvotes: 0

Views: 1557

Answers (1)

gmoshkin
gmoshkin

Reputation: 1135

pThirdPart points to the address of thirdPart, not the address pointed to by *thirdPart.

You are probably confused because the address of an array is not the same as the address of a pointer. When you have an array like so

char array[10];

taking the address of this variable is the same as just referencing it without and index. array is the same value as &array.

But with a pointer the situation is different

char *pointer;

pointer is not the same value as &pointer

This is just a quirk of C/C++ that you have to be aware of.

So in your program you should have

BYTE *pFirstPart = reinterpret_cast<BYTE*>(&firstPart);
BYTE *pSecondPart = reinterpret_cast<BYTE*>(&secondPart);
BYTE *pThirdPart = reinterpret_cast<BYTE*>(thirdPart);

or even

BYTE *pFirstPart = reinterpret_cast<BYTE*>(firstPart);
BYTE *pSecondPart = reinterpret_cast<BYTE*>(secondPart);
BYTE *pThirdPart = reinterpret_cast<BYTE*>(thirdPart);

both variants will work.

Upvotes: 2

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