I am making a c++ qt program and I need to write data to a binary file. But there's a problem. When I do this, extra empty bytes are written to the file. Here is my code:
QDataStream output(&fileOut);
QBitArray result;
result.resize(8);
result.fill(true);
output << result;
As a result, my file consists of 5 bytes instead of 1:
00000000
00000000
00000000
00001000
11111111
Does anyone know how to solve this problem?
Using QDataStream to write binary data in any form which should not be read again by QDataStream will not work since QDataStream adds some more bytes to be able to deserialize the data later on. QDataStream is not meant to write plain data (as can be seen in the documentation) - use QFile::write() for it.
A data stream is a binary stream of encoded information which is 100% independent of the host computer's operating system, CPU or byte order. For example, a data stream that is written by a PC under Windows can be read by a Sun SPARC running Solaris. So it's universal and do not mislead people
So it's universal and do not mislead people - yes, it's universal in the way that it can be read and write from/to QDataStream on different platforms. But it's data format is not specified so you can not read it with something without known the Qt internals.For example QTcpSocket is realized on top of QDataStream, - no, QTcpSocket does not use QDataStream at all - you can send your data encoded as a QDataStream through a QTcpSocket but you have to read it on the other side with QDataStream too.For example QTcpSocket is realized on top of QDataStream, but it works with any socket. I should be more correct, i wanted to say, that QDataStream provides serialization of binary data to a QIODevice, while QIODevice provides both a common implementation and an abstract interface for devices that support reading and writing of blocks of data, such as QFile, QBuffer and QTcpSocket. So you are free to use QDataStream to write/read to/from any stream without worry how this data would be read on another end.There may be some under the hood conversion shenanigans w/ qBitArray being sent to a stream.
QDatastream resource
qt, but for standard C++, you have to use the stream'swritefunction to specify the exact number of bytes to write, and not use<<. This is especially the case if you're writing the file as "binary", where you need total control of how many bytes are written.