Qt, QFile write on specific line
Solution 1
If the line you want to insert into the file is always the last line (as the function 1 suggest) you can try to open the file in append mode using QIODevice::Append in your Write method.
If you want to insert a line in the middle of the file, I suppose an easy way is to use a temp file (or, if it is possible, to load the lines into a QList, insert the line and write the list back to the file)
Solution 2
QString fileName = "student.txt";
QFile mFile(fileName);
if(!mFile.open(QFile::Append | QFile::Text)){
qDebug() << "Could not open file for writing";
return 0;
}
QTextStream out(&mFile);
out << "The magic number is: " << 4 << "\n";
mFile.close();
The above code snippet will append the text "The magic number is: 4" , at the end of the file.
![Gabriel](https://i.stack.imgur.com/QipEc.png?s=256&g=1)
Comments
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Gabriel about 2 years
I've run into another problem in Qt, I can't seem to figure out how to write on a specific line on a text file with
QFile
. Instead, everything is erased written at the beginning. So with the given information, how would I write to a specific line inQFile
?Here are two functions.
- The first function searches a file, and then gets two variables. One that finds the next empty line, one that gets the current ID number.
- Second function is supposed to write. But I've looked for documentation on what I need, I've googled it and tried many searches to no avail.
Function 1
QString fileName = "C:\\Users\\Gabe\\SeniorProj\\Students.txt"; QFile mFile(fileName); QTextStream stream(&mFile); QString line; int x = 1; //this counts how many lines there are inside the text file QString currentID; if(!mFile.open(QFile::ReadOnly | QFile::Text)){ qDebug() << "Could not open file for reading"; return; } do { line = stream.readLine(); QStringList parts = line.split(";", QString::KeepEmptyParts); if (parts.length() == 3) { QString id = parts[0]; QString firstName = parts[1]; QString lastName = parts[2]; x++; //this counts how many lines there are inside the text file currentID = parts[0];//current ID number } }while (!line.isNull()); mFile.flush(); mFile.close(); Write(x, currentID); //calls function to operate on file }
The function above reads the file, which looks like this.
1001;James;Bark 1002;Jeremy;Parker 1003;Seinfeld;Parker 1004;Sigfried;FonStein 1005;Rabbun;Hassan 1006;Jenniffer;Jones 1007;Agent;Smith 1008;Mister;Anderson
And the function gets two bits of information that I figured I might need. I'm not too familiar with
QFile
and searching, but I thought that I'd need these variables:int x; //This becomes 9 at the end of the search. QString currentID; //This becomes 1008 at the end of the search.
So I passed in those variables to the next function, at the end of function 1.
Write(x, currentID);
Function 2
void StudentAddClass::Write(int currentLine, QString idNum){ QString fileName = "C:\\Users\\Gabe\\SeniorProj\\Students.txt"; QFile mFile(fileName); QTextStream stream(&mFile); QString line; if(!mFile.open(QFile::WriteOnly | QFile::Text)){ qDebug() << "Could not open file for writing"; return; } QTextStream out(&mFile); out << "HelloWorld"; }
I've left out any attempts at fixing the problem myself, all this function does is replace all the contents of the text file with "HelloWorld".
Does anyone know how to write on a specific line, or at least go to the end of the file and then write?
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Gabriel about 12 yearsI might have to copy it all and then put into the new file. I tried using append but I'm not to sure how to use it ^_^
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Gianluca about 12 yearsopen the file with mFile.open(QFile::Append | QFile::Text)
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Gabriel about 12 yearsand then what? There still aren't any functions that I know of to work on 1 line...
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Gianluca about 12 yearsand then write the line (your
out << "HelloWorld"
line). Opening the file in append mode set the current pointer of the file to the end of it, which is what you don't do in yourWrite
method and so you write the new line at the beginning of the file. -
Neurotransmitter almost 8 yearsAnd how to write text to, say, 2nd line of 1000?