I have a QByteArray with 4 values in little endian format
QByteArray ba;
ba.append(0xbb);
ba.append(0x1c);
ba.append(0x51);
ba.append(0x1e);
to convert ba to big endian I do the following :
baBigEndian[0] = ba[3];
baBigEndian[1] = ba[2];
baBigEndian[2] = ba[1];
baBigEndian[3] = ba[0];
to convert the big endian array to an unsigned long i tried the following:
baBigEndian.toULong(&ok,10);
The little endian byte array is correctly converted to big endian but the .toULong returns 0 in stead of 508632251.
How can I convert the baBigEndian array to an unsigned long? Or is there a way to directly convert from a little endian array to an unsigned long?
Thanks in advance!
toULong()
won't work, since it expects the QByteArray to contain a string representation of the number in ASCII format (eg "0xbb1c511e"
, which is 10 ASCII bytes), and your QByteArray contains the literal binary bytes instead (eg 0xbb1c511e
, which is 4 binary bytes).
Assuming your QByteArray contains the four bytes in big-endian format (as it does after step 2 in your example code), then this would work:
unsigned long val = ntohl(*((const unsigned long *)ba.data()));
Note however that sizeof(unsigned long)
is not guaranteed to be 4 bytes on all platforms, so you'd be better off using a fixed-width type that is guaranteed to always be 4 bytes wide instead, eg
quint32 val = ntohl(*((const quint32 *)ba.data()));
Try memcpy
quint32 value = 0; //or qint32
memcpy(&value, baBigEndian.data(), sizeof(quint32));//or baBigEndian instead baBigEndian.data() if you use plain array instead QByteArray
Also, it can be done with reinterpret_cast
but I do not recommend you to use reinterpret_cast
because I had some problems on arm
processors (while on x86
it works fine).
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