Compare two numbers in a QString-CodePudding

There are two values:

QString str1 = "3.5.8", str2 = "20.3.6";

Let's imagine that these two numbers represent the software version, as it were.

It is known that QString compares character-by-character.

What if we approach this decision in this way:

str1.replace(".","");
str2.replace(".","");
int n = str1.toInt();
int m = str2.toInt();

if (n >= m)
{
    qDebug() << "YES";
} else if (n <= m) {
    qDebug() << "NO";
}

Maybe there is a more optimal and correct way to do this.

Could you tell me please how I can translate these values into numbers so that they can be compared in their entirety. Thanks.

CodePudding user response：

The QVersionNumber class was designed to solve this problem (requires Qt 5.6 ):

QVersionNumber version1 = QVersionNumber::fromString(str1);
QVersionNumber version2 = QVersionNumber::fromString(str2);

if (version1 > version2)
{
    qDebug() << "YES";
}
else
{
    qDebug() << "NO";
}

CodePudding user response：

Quite frankly I'd first parse them to real ints, and then convert those; something like this:

const std::string s1  = str1.toStdString();
const std::string s2  = str2.toStdString();
struct { int major, minor, tag; } v0, v1;
int r1=sscanf(s1.c_str(),"%i.%i.%i",&v0.major,&v0.minor,&v0.tag);
...

Then you can compare versions on major/minor/etc as you require. Of course you do want to add some error-checking on the result of sscanf, and possibly look into sscanf_s for safety concerns.

CodePudding user response：

Use split method to have QStringLists, use std::transform to convert them to vector<int>, finally use lexicographical_compare.

Suboptimal performance-wise, verbose, but correct and idiomatic.