Upplite trading options32 comments
Rm binary options hot tips for indian stock market eurocapital
QByteArray is an Array of Chars. The class offers many convenient features, such as the ability to resize the array at any time. Once you start using it, you will abandon the archaic memcpy and memset functions. And if your application tries to access an element that is out of bounds, you will get a run-time warning. It is very similar to an old-fashioned C-style char array, only nicer. QByteArray is an explicitly shared class.
This makes the class more efficient in most cases, but can lead to subtle bugs. You can use these options to test your programs. QByteArray is the perfect class to store non-textual data in memory. QCString is a String of Chars. The C vocabulary consisted of scientific and technical terms which it behooved no one but scientists and technicians to use. We call copy to obtain a deep copy of the array. If it isn't, make it so:.
QCString 's main benefit is that it requires only about half the memory of QString , but this is rarely an issue. In general QString is the best class to use for user-visible strings, not least because it uses Unicode. QString is a Unicode String. But why do you need to mix one- and two-byte characters anyway? The QString class stores a bit Unicode string. Qt provides operators and constructors to convert from one to the other conveniently, but that's not always enough.
But if the QString contains non-Latin-1 characters, the result is undefined. This will ensure that you must call latin1 explicitly:. If you use qmake , you can disable the conversion for your whole project by adding this line to the. There are other ways of converting a QString to a QCString see the QString and QTextCodec class documentation ; the utf8 function is one way, and it has the advantage of preserving all the information:.
QCString doesn't mandate a particular encoding. If you use encodings other than Latin-1, this automatic conversion is dangerous. A similar function exists for UTFencoded strings.
The following rules of thumb can help you achieve faster, more reliable code: Choose your data types carefully. Check that the necessary conversions are correct. Neither prospect is very attractive. And here's how to read a bit signed integer in big endian the default from a file called "gritty":.
QDataStream supports a lot of types: Here's the code to write out the value of the properties:. The file starts with a bit magic number, then an 8-bit version that specifies which version of QDataStream is used to write out the data. When inputting or outputting complex types such as QVariant , it's very important to make sure that the same version of the stream is used for reading and writing.
If you need both forward and backward compatibility, you can hardcode the version number in the application:. The disadvantage of hardcoding is that the application will not benefit from improvements in Qt 3. In the following code snippet, we use writeProperties and readProperties to save a frame's properties across sessions:. The image's width and height are the first two fields of the image header "IHDR" chunk. Here's the complete code source of a Qt program that prints out the width and height of the PNG images specified on the command line:.
Now let's suppose that we have a PNG image embedded in our application using qembed or a similar tool:. How can we determine the size of that image without creating a QImage? The answer follows from these four facts: A char array can be converted into a QByteArray. Here's how to transform these ideas into running code:. By default, it uses the 8-bit encoding prescribed by the locale Latin-1 in most of Europe.
If you want QTextStream s to work seamlessly in any locale, you usually need to reflect on the type of data that you are dealing with. QTextStream can even operate on a QString. And here's how to simulate cout with QTextOStream:.