QT Creator，返回（C ++）

Question

Could somebody explain me why are these 2 types of return used?

int parse(QTextStream& out, const QString fileName) {
    QDomDocument doc;
    QFile file(fileName);
    if (!file.open(QIODevice::ReadOnly|QIODevice::Text)) {
        out<<"Datei "<<fileName<<" nicht lesbar"<<endl;


>   return 1;

    }
    QString errorStr;
    int errorLine;
    if (!doc.setContent(&file, false, &errorStr, &errorLine)) {
        out<<"Fehler in Zeile "<<errorLine<<": "<<errorStr<<endl;


>  return 2;

    }
    ...
}

Here stays a part of another program.Why the code here doesn`t work the same way with

return 0;

?

int main(int argc, char *argv[])
{
    QTextStream out(stdout);
       out.setCodec("UTF-8");
       if (argc != 3) {
           out<<"Usage: "<<argv[0]<<"   XML-Datei ist nicht vorhanden."<<endl;
           return(1);
       }
       List wayList(out, argv[1]);
       out<<"DOM-Baum gelesen."<<endl;
       wayList.convert(argv[2]);

return 1;

}

Answer 1

In your first example, the function returns early to indicate an error . The file couldn't be opened so the function returns a value to the caller of that function. Couldn't set content, function returns a different value to the caller.

if (!file.open(QIODevice::ReadOnly|QIODevice::Text)) {
    out<<"Datei "<<fileName<<" nicht lesbar"<<endl;

    return 1; // return value to caller
}

A function could for example call parse and check it's return value for success:

if ((parse(args...)) == 0) // success

In the end of function main() , return 0; indicates that the program ran successfully.