How to convert QString to int?

You don't have all digit characters in your string. So you have to split by space

QString Abcd = "123.5 Kb";
Abcd.split(" ")[0].toInt();    //convert the first part to Int
Abcd.split(" ")[0].toDouble(); //convert the first part to double
Abcd.split(" ")[0].toFloat();  //convert the first part to float

Update: I am updating an old answer. That was a straight forward answer to the specific question, with a strict assumption. However as noted by @DomTomCat in comments and @Mikhail in answer, In general one should always check whether the operation is successful or not. So using a boolean flag is necessary.

bool flag;
double v = Abcd.split(" ")[0].toDouble(&flag); 
if(flag){
  // use v
}

Also if you are taking that string as user input, then you should also be doubtful about whether the string is really splitable with space. If there is a possibility that the assumption may break then a regex verifier is more preferable. A regex like the following will extract the floating point value and the prefix character of 'b'. Then you can safely convert the captured strings to double.

([0-9]*\.?[0-9]+)\s+(\w[bB])

You can have an utility function like the following

QPair<double, QString> split_size_str(const QString& str){
    QRegExp regex("([0-9]*\\.?[0-9]+)\\s+(\\w[bB])");
    int pos = regex.indexIn(str);
    QStringList captures = regex.capturedTexts();
    if(captures.count() > 1){
        double value = captures[1].toDouble(); // should succeed as regex matched
        QString unit = captures[2]; // should succeed as regex matched
        return qMakePair(value, unit);
    }
    return qMakePair(0.0f, QString());
}

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Don't forget to check if the conversion was successful!

bool ok;
auto str= tr("1337");
str.toDouble(&ok); // returns 1337.0, ok set to true
auto strr= tr("LEET");
strr.toDouble(&ok); // returns 0.0, ok set to false

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The string you have here contains a floating point number with a unit. I'd recommend splitting that string into a number and unit part with QString::split().

Then use toDouble() to get a floating point number and round as you want.

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You can use:

QString str = "10";
int n = str.toInt();

Output:

n = 10

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Use .toInt() for int .toFloat() for float and .toDouble() for double

toInt();

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As a suggestion, you also can use the QChar::digitValue() to obtain the numeric value of the digit. For example:

for (int var = 0; var < myString.length(); ++var) {
    bool ok;
    if (myString.at(var).isDigit()){
        int digit = myString.at(var).digitValue();
        //DO SOMETHING HERE WITH THE DIGIT
    }
}

Source: Converting one element from a QString to int

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On the comments:

sscanf(Abcd, "%f %s", &f,&s);

Gives an Error.

This is the right way:

sscanf(Abcd, "%f %s", &f,qPrintable(s));

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