I am using Qt5 and errors exist from this line of codes after running sample project I found on the internet.
QFile f( "world.txt" );
if( f.open( QIODevice::ReadOnly ) ) {
QTextStream ts( &f );
Vertex v[3];
int vcount = 0;
bool allok, ok;
while( !ts.atEnd() )
{
QStringList line = QString::split( " ",ts.readLine().simplifyWhiteSpace() );
Errors are:
split is not a member of QStringList
simplifyWhiteSpace is not a member of QString
I don't know how to convert the line to work on Qt5.
Both QStringList::split() and QString::simplifyWhitespace() were functions in Qt3, and have been renamed or moved for Qt5 (which you are using according to your tags).
For QStringList::split(), the documentation says:
Use QString::split(sep, QString::SkipEmptyParts) or QString::split(sep, QString::KeepEmptyParts) instead.
Be aware that the QString::split()'s return value is a QStringList that always contains at least one element, even if str is empty.
You already changed this in your edit, so you are left with QString::simplifyWhitespace(), where the documentation says:
QString QString::simplifyWhiteSpace () const
Use simplified() instead.
Related
I have custom(dynamic QString) for example something like this 123+555 and i need to get this after +.Also there can be something different then + (/,*,- etc.). My question is how to get part of string after some char.
Use the split function, which allows you to specify the separator and returns a list of the elements.
QString string("123+555");
QStringList listItems = string.split('+', QString::SkipEmptyParts);
QString finalString = listItems[1];
Alternatively, you can find by index the separating character location and use that with a call to right
Since you're usin Qt, you could try the class: QRegExp.
With such class you could write code like this:
// This code was not tested.
QRegExp rx("(\\d+)(\\+|\\-|\\*|/)(\\d+)"); // Be aware, I recommend you to read the link above in order to see how construct the proper regular expression.
int pos = rx.indexIn("23+344");
if (pos > -1) {
QString number_1 = rx.cap(1); // "23"
QString op = rx.cap(2); // "+"
QString number_2 = rx.cap(3); // "344"
// ...
}
This way you don't have to write code to check which of the characters(operators) "+, -, *, /" is present to then perform a split on the string depending on what character was found.
I am writing data to a config file using the following code.
QSettings settings("/root/configFile.ini",QSettings::IniFormat);
QString userName = lineEditUsername.text();
QString password = lineEditPassword.text();
QList<QString> listUsername;
QList<QString> listPassword;
settings.beginWriteArray("UserData");
for(i=0;i<listUsername.size();i++)
{
Qstring user = listUsername.at(i);
Qstring pass = listPassword.at(i);
settings.setArryIndex(i);
settings.setValue("Username",user);
settings.setValue("Password",pass);
}
settings.endArray();
}
Now when I run the code first time and give 4 or 5 values they are formed in proper order in the file. However if I run the application for second time the values start overwriting from first position. Can some one suggest me some solution for this?
Instead of creating and maintaining arrays and indexes, I would propose to create user credentials map and store it in the settings file as follows:
QSettings settings("/root/configFile.ini", QSettings::IniFormat);
QString userName = lineEditUsername.text();
QString password = lineEditPassword.text();
QList<QString> listUsername;
QList<QString> listPassword;
//settings.beginWriteArray("UserData");
QVariantMap userDataMapping;
for(int i = 0; i < listUsername.size() ; i++)
{
QString user = listUsername.at(i);
QString pass = listPassword.at(i);
userDataMapping[user] = pass;
//settings.setArryIndex(i);
//settings.setValue("Username",user);
//settings.setValue("Password",pass);
}
// Store the mapping.
settings.setValue("UserData", userDataMapping);
//settings.endArray();
// ...
This will store your data in ini file in the following format:
UserData=#Variant(\0\0\0\b\0\0\0\x1\0\0\0\x6\0\x64\0\x64\0\x64\0\0\0\n\0\0\0\x6\0\x62\0\x62\0\x62)
When you read settings, do something like this:
[..]
QVariant v = settings.value("UserData");
QVariantMap map = v.value<QVariantMap>();
QMapIterator<QString, QVariant> i(map);
while (i.hasNext()) {
i.next();
QString user = i.key();
QString pass = i.value().toString();
}
You need to retrieve the amount of existing entries before adding a new one. Something like this:
int size = settings.beginReadArray( "UserData" );
settings.endArray();
settings.beginWriteArray( "UserData" );
settings.setArrayIndex( size ); // Note: Maybe 'size - 1', not sure
// ...
settings.endArray();
setArrayIndex( size ) will move the array index to the end and will thus no longer override an existing entry
How can i find a specific character in a QFile which has a text in it?
for example i have ' $5000 ' written somewhere in my file. in want to find the "$" sign so i will realize that I've reached the number.
I tried using QString QTextStream::read(qint64 maxlen) by putting 1 as the maxlen :
QFile myfile("myfile.txt");
myfile.open(QIODevice::ReadWrite | QIODevice::Text);
QTextStream myfile_stream(&myfile);
while(! myfile_stream.atEnd())
{
if( myfile_stream.read(1) == '$')
{
qDebug()<<"found";
break;
}
}
and i get "error: invalid conversion from 'char' to 'const char* "
i also tried using the operator[] but apparently it can't be used for files.
Read in a line at a time and search the text that you've read in
QTextStream stream(&myFile);
QString line;
do
{
line = stream.readLine();
if(line.contains("$"))
{
qDebug()<<"found";
break;
}
} while (!line.isNull());
The error message you've posted doesn't match the issue in your code. Possibly the error was caused by something else.
QTextStream::read returns QString. You can't compare QString and const char* directly, but operator[] can help:
QString s = stream.read(1);
if (s.count() == 1) {
if (s[0] == '$') {
//...
}
}
However reading a file by too small pieces will be very slow. If your file is small enough, you can read it all at once:
QString s = stream.readAll();
int index = s.indexOf('$');
If your file is large, it's better to read file by small chunks (1024 bytes for example) and calculate the index of found character using indexOf result and count of already read chunks.
a single char could be read with
QTextStream myfile_stream(&myfile);
QChar c;
while (!myfile_stream.atEnd())
myfile_stream >> c;
if (c == '$') {
...
}
myfile_stream.read(1) - this is not good practice, you should not read from file one byte at a time. Either read the entire file, or buffered/line by line if there is a risk for the file to be too big to fit in memory.
The error you get is because you compare a QString for equality with a character literal - needless to say that is not going to work as expected. A string is a string even if there is only one character in it. As advised - use either the [] operator or better off for reading - QString::at() const which is guaranteed to create no extra copy. You don't use it on the QFile, nor on the QTextStream, but on the QString that is returned from the read() method of the text stream targeted at the file.
Once you have the text in memory, you can either use the regular QString methods like indexOf() to search for the index of a contained character.
in want to find the "$" sign so i will realize that I've reached the
number.
It sounds to me that you're searching for the '$' symbol because you're more interested in the dollar value that follows it. In this case, I suggest reading the files line by line and running them through a QRegExp to extract any values you're looking for.
QRegExp dollarFind("\\$(\\d+)");
while(!myfile_stream.atEnd()){
QString line = myfile_stream.readLine();
if (dollarFind.exactMatch(line)){
QStringList dollars = dollarFind.capturedTexts();
qDebug() << "Dollar values found: " << dollars.join(", ");
}
}
Using Qt, I want this code to work:
QList<QPair<QString, QString>> list;
foreach (QPair<QString, QString> pair, list)
{
}
instead, I get the error:
'pair' : undeclared identifier
Using a typedef I can make it work, but this is not what I want (unless this is the only thing that works):
typedef QPair<QString, QString> MyPair;
QList<MyPair> list;
foreach (MyPair pair, list)
{
}
Can anyone explain why the first foreach doesn't compile?
it's not the foreach error. It's declaration error. You declared list like this:
QList<QPair<QString, QString>> list;
while it should this way:
QList<QPair<QString, QString> > list;
Just declare QPair outside of loop:
QPair<QString,QString> pair;
foreach(pair,list){
}
It is not possible to use template classes inside qt foreach statement which contains more than one template parameter, because comma separator conflicts with comma separator inside macros.
#define add( a, b ) (a + b)
template < typename T1, typename T2 >
struct DATA
{
static const T1 val1 = 1;
static const T2 val2 = 2;
};
// Usage
const int c = add( 1, 2 ); // OK
const int d = add( DATA< int, int >::val1 , DATA< int, int >::val2 ); // FAIL
because macros add will interpret "DATA< int" as first argument, and " int >::val1" as second, and so on.
Some explanation with above answer... if your compiler accept
QList<QPair<QString, QString>> list;
giving no error on such declaration, reasons for topic caster error is different and indeed has to do with a fact that declaration must be done outside of foreach() loop. That's explained in QT documentation.
regarding >> and > >... that's old story and latest GCC (so linux/mac) consider it to be a syntax mistake, because it's not conforming standard. >> in GCC manner is treated as operator with all follow-up errors..
My task is custom sorting items in QStandardItemModel.
By default for a sequance of rows
text1
text11
text12
text100
text110
text120
text1110
function QStandardItemModel::sort() sorting it as
text1
text100
text11
text110
text1110
text12
text120
I want that would be
text1
text11
text12
text100
text110
text120
text1110
For this purpose I overload function int QString::compare(const QString &s) const in the separeted compare.cpp file.
int QString::compare(const QString &s) const
{
QString strL = "";
strL.append(this);
QString strR = "";
strR.append(s);
QStringList list = strL.split(QRegExp("\\D+"),QString::SkipEmptyParts);
foreach (QString num, list) {
strL.replace(num, QString("%1").arg(num,10,'0'));
}
list = strR.split(QRegExp("\\D+"),QString::SkipEmptyParts);
foreach (QString num, list) {
strR.replace(num, QString("%1").arg(num,10,'0'));
}
return strL.localeAwareCompare(strR);
}
that using in operator
virtual bool operator< ( const QStandardItem & other ) const.
Such function as compare can be redefined in the separate file and it is simple to add it in *.pro and easy application will find its realization. But with more difficult applications such way it is impossible. Please tell me Why?
Example : code
Rather than using a QStandardItemModel directly, you want to wrap it in a QSortFilterProxyModel. This class was designed for exactly the situation you describe--when you want to implement custom sorting or filtering behavior. Just implement the QSortFilterProxyModel::lessThan method to reflect the desired behavior.
QStandardItemModel has a virtual function sort(int column, Qt::SortOrder order = Qt::AscendingOrder). I think it will be easier to subclass QStandardItemModel and reimplement sortfunction.
I did!
When i said "heavy application", i means application, that contains and binds many other plugins and libs. And for this purpose what I create the new lib with name QStringCompare, that contains one file compare.cpp with my new definiotoin of compare:
#include <QStringList>
#include <QRegExp>
int Q_DECL_EXPORT QString::compare(const QString &s) const
{
QString strL = "";
strL.append(this);
QString strR = "";
strR.append(s);
QStringList list = strL.split(QRegExp("\\D+"),QString::SkipEmptyParts);
foreach (QString num, list) {
strL.replace(num, QString("%1").arg(num,10,'0'));
}
list = strR.split(QRegExp("\\D+"),QString::SkipEmptyParts);
foreach (QString num, list) {
strR.replace(num, QString("%1").arg(num,10,'0'));
}
return strL.localeAwareCompare(strR);
}
and it links QStringCompare.lib to *.pro of Main apllication of my project. Generally it's not necessary to declare it in *.h files. All other plug-ins inherit this redefinition. The experiments showed that it is necessary to links to main application.
As that so.
There can be I am mistaken in reasonings, but it's working on linux and windows.
This is source of QStringCompare.libs. You can try.