QT的QFile没有提供定位到具体那一行的函数，只是提供了seek函数。
qint64 QIODevice::readLine ( char * data, qint64 maxSize )
This function reads a line of ASCII characters from the device, up to a maximum of maxSize - 1 bytes, stores the characters in data, and returns the number of bytes read. If a line could not be read but no error ocurred, this function returns 0. If an error occurs, this function returns what it could the length of what could be read, or -1 if nothing was read.
A terminating '\0' byte is always appended to data, so maxSize must be larger than 1.
Data is read until either of the following conditions are met:
The first '\n' character is read.
maxSize - 1 bytes are read.
The end of the device data is detected.
For example, the following code reads a line of characters from a file:
QFile file("box.txt");
if (file.open(QFile::ReadOnly)) {
char buf[1024];
qint64 lineLength = file.readLine(buf, sizeof(buf));
if (lineLength != -1) {
// the line is available in buf
}
}
The newline character ('\n') is included in the buffer. If a newline is not encountered before maxSize - 1 bytes are read, a newline will not be inserted into the buffer. On windows newline characters are replaced with '\n'.
This function calls readLineData(), which is implemented using repeated calls to getChar(). You can provide a more efficient implementation by reimplementing readLineData() in your own subclass.
See also getChar(), read(), and write().
