C++ Truncation of constant value

Question

I'm getting this warning

warning C4309: 'initializing' : truncation of constant value

and when I try to execute my dll it only sends 4 bytes instead of the 10 bytes.
What could be wrong?

Here is my code:

int WINAPI MySend(SOCKET s, const char* buf, int len, int flags)
{

    cout << "[SEND:" << len << "] ";

    for ( int i = 0; i < len; i++ ) {
        printf( "%02x ", static_cast<unsigned char>( buf[i] ) );
    }

    printf("\n");

    //causing the warning:
    char storagepkt[] = {0x0A, 0x00, 0x01, 0x40, 0x79, 0xEA, 0x60, 0x1D, 0x6B, 0x3E};

    buf = storagepkt;
    len = sizeof(storagepkt);

    return pSend(s, buf, len, flags);
}

---

UPDATE

int (WINAPI *pSend)(SOCKET s, const char* buf, int len, int flags) = send;
int WINAPI MySend(SOCKET s, const char* buf, int len, int flags);

---

UPDATE

As suggested I tried memcpy:

memcpy((char*) buf, storagepkt, sizeof(storagepkt));

---

UPDATE

unsigned char storagepkt[] = {0x0A, 0x00, 0x01, 0x40, 0x79, 0xEA, 0x60, 0x1D, 0x6B, 0x3E};

Fixed it.

Answer 1

You're initializing a buffer of char which is signed. Anything over 0x7f is beyond what it can handle and will be converted to a negative number. The actual data is probably OK and you can ignore the warning, although it would be better to make it unsigned char.

As for why it's only sending 4 bytes, that sounds suspiciously like the size of a pointer. Are you sure the code is exactly as you've represented it, using an array, rather than a pointer passed to a function? A function doesn't know the size of an array even when you declare the parameter as an array - you need to pass the size of the array into the function.

Answer 2

I can reproduce this warning with the following code:

char aa = 0xff;

the warning is solved with

unsigned char aa = 0xff;

(as Mark Ransom already pointed out, I just added a minimal sample code to reproduce the warning)