change the positions of characters in a string

[arunvv]

Hi

I want to change the positions of characters in a string.
Ex: QString x = "341256";
I want to Change the x string from "341256" to "123456";

How can I change the character positions within a string.

Thanks & Regards,
Arun.

[wysota]

You mean you want to sort it or make an arbitrary change?

This might just work:

QString str = "341256";
QChar *dat = str.data();
qSort(dat, dat+str.length());

QString str = "341256";
QChar *dat = str.data();
qSort(dat, dat+str.length());

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If you want arbitrary changes then swap characters manually.

QString str="342516";
qSwap(str[2], str[3]);

QString str="342516";
qSwap(str[2], str[3]);

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[arunvv]

Thanks for your reply.
I gave me error if I am trying to swap characters using qswap. It seems to me qswap is used to swap a whole string, not to swap individual characters inside the string.

So I resolved the issue by converting QString to Std C++ string and using the method which you stated in reply i.e. swapping.

Resolved as Shown here:

classname::function()
{
        ....
        QString str = "341256";
        char * str1;
	str1 = (char *)Q_date.toAscii().constData();
	swap( str1[0], str1[2] );	
	swap( str1[1], str1[3] );	
	str = (const char *)str1; // Now str has string "123456"
 
       ....
}
void  clasname::swap(char &a,char& b )
{
 char temp = b;
 b = a;
 a = temp;
}

classname::function()
{
        ....
        QString str = "341256";
        char * str1;
	str1 = (char *)Q_date.toAscii().constData();
	swap( str1[0], str1[2] );	
	swap( str1[1], str1[3] );	
	str = (const char *)str1; // Now str has string "123456"
         
       ....
}
void  clasname::swap(char &a,char& b )
{
 char temp = b;
 b = a;
 a = temp;
}

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Thanks again for giving me idea of swapping.

[jpn]

Even if qSwap() doesn't work as expected, it compiles fine for me at least:

QString str("12");
qSwap(str[0], str[1]); 
qDebug() << str; // "22"

QString str("12");
qSwap(str[0], str[1]); 
qDebug() << str; // "22"

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However, the first method suggested by Wysota works perfectly.

QString str("341256");
QChar* dat = str.data();
qSort(dat, dat + str.length());
qDebug() << str; // "12345"

QString str("341256");
QChar* dat = str.data();
qSort(dat, dat + str.length());
qDebug() << str; // "12345"

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[wysota]

However, the first method suggested by Wysota works perfectly.

So this will work as well:

QString str="173562";
QChar *dat = str.data();
qSwap(dat[1], dat[2]);

QString str="173562";
QChar *dat = str.data();
qSwap(dat[1], dat[2]);

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[spud]

The following code will in most likely cause your application to crash:

char * str1 = Q_date.toAscii().constData();
swap( str1[0], str1[2] );

char * str1 = Q_date.toAscii().constData();
swap( str1[0], str1[2] );

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and even if it doesn't it won't work.
You shouldn't save a pointer to the temporary object returned by toAscii(), it goes out of scope immediately. Go with Wysota's suggestion.

@jpn + wysota: It's an interesting side effect of Qt's trick with QCharRef that swap doesn't work as expected. I think they should mention QCharRef in the documentation and that it's sometimes more efficient(in this case necessary) to work on the raw QChar array returned by data()