How to Get substring from given QString in Qt - c++

Question

I have a QString like this:
QString fileData = "SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication"
What I need to do is to create substrings as follow:
SoftwareName = MY_DISPLAY_OS //text after ':'
Version = 10.25.10086-1
Release = 2022-3
I tried using QString QString::sliced(qsizetype pos, qsizetype n) const but didn't worked as I'm using 5.9 and this is supported on 6.0.
QString fileData = "SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication";
QString SoftwareName = fileData.sliced(fileData.lastIndexOf(':'), fileData.indexOf('.'));
Please help me to code this in Qt.

Answer 1

Use QString::split 3 times:
Split by QLatin1Char('=') to two parts:
SOFT_PACKAGES.ABC
MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication
Next, split 2nd part by QLatin1Char(':'), probably again to just 2 parts if there can never be more than 2 parts, so the 2nd part can contain colons:
MY_DISPLAY_OS
MY-Display-OS.2022-3.10.25.10086-1.myApplication
Finally, split 2nd part of previous step by QLatin1Char('.'):
MY-Display-OS
2022-3
10
25
10086-1
myApplication
Now just assemble your required output strings from these parts. If exact number of parts is unknown, you can get Version = 10.25.10086-1 by removing two first elements and last element from the final list above, and then joining the rest by QLatin1Char('.'). If indexes are known and fixed, you can just use QStringLiteral("%1.%2.%3").arg(....

Answer 2

One way is using
QString::mid(int startIndex, int howManyChar);
so you probably want something like this:
QString fileData = "SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication";
QString SoftwareName = fileData.mid(fileData.indexOf('.')+1, (fileData.lastIndexOf(':') - fileData.indexOf('.')-1));
To extract the other part you requested and if the number of '.' characters remains constant along all strings you want to check you can use the second argument IndexOf to find shift the starting location to skip known many occurences of '.', so for example
int StartIndex = 0;
int firstIndex = fileData.indexOf('.');
for (int i=0; i<=6; i++) {
StartIndex += fileData.indexOf('.', firstIndex+StartIndex);
}
int EndIndex = fileData.indexOf('.', StartIndex+8);
should give the right indices to be cut out with
QString SoftwareVersion = fileData.mid(StartIndex, EndIndex - StartIndex);
If the strings to be parsed stay less consistent in this way, try switching to regular expressions, they are the more flexible approach.

Answer 3

In my experience, using regular expressions for these types of tasks is generally simpler and more robust. You can do this with a regular expressions with the following:
// Create the regular expression.
// Using C++ raw string literal to reduce use of escape characters.
QRegularExpression re(R"(.+=([\w_]+):[\w-]+\.(\d+-\d+)\.(\d+\.\d+\.\d+-?\d+))");
// Match against your string
auto match = re.match("SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication");
// Now extract the portions you are interested in
// match.captured(0) is always the full string that matched the entire expression
const auto softwareName = match.captured(1);
const auto version = match.captured(3);
const auto release = match.captured(2);
Of course for this to make sense, you have to understand regex, so here is my explanation of the regex used here:
.+=([\w_]+):[\w-]+\.(\d+-\d+)\.(\d+\.\d+\.\d+-?\d+)
.+=
get all characters up to and including the first equals sign
([\w_]+)
capture one or more word characters (alphanumeric characters) or underscores
:
a colon
[\w-]+\.
one or more alphanumeric or dash characters followed by a single period
(\d+-\d+)
capture one or more of digits followed by a dash followed by one or more digits
\.
a single period
(\d+\.\d+\.\d+-?\d*)
capture three sets of digits with periods in between, then an optional dash, and any number of digits (could be zero digits)
I think it is generally easier to make a regex that handles changes to the input - lets say version becomes 10.25.10087 - more easily than manually parsing things by index.
Regex is a powerful tool once you get used to it, but it can certainly seem daunting at first.
Example of this regex on regex101.com: https://regex101.com/r/dj3Z4U/1