Shulou(Shulou.com)06/02 Report--

This article mainly explains "what is the use method of Qt QFile file operation", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let Xiaobian take you to learn "What is the use method of Qt QFile file operation"!

Many applications require the ability to manipulate files, including reading/writing file content, creating and deleting files, etc. Some applications are even born purely to manipulate files, such as WPS Office, PDFedit, etc. To this end, the Qt framework provides the QFile class specifically designed to manipulate files.

QFile file manipulation

QFile class supports reading, writing, deleting, renaming, copying and other operations on files. It can operate both file files and binary files.

Before you can manipulate files using the QFile class, you need to introduce header files into your program. To create objects of QFile class, common constructors are:

QFile::QFile()QFile::QFile(const QString &name)

Parameter name is used to specify the target file to be operated on, including the storage path and file name of the file. The storage path can be an absolute path (such as "D:/Demo/test.txt") or a relative path (such as "./ Demo/test.txt"), the delimiter in the path should be represented by"/".

Usually, we call the second constructor, which directly indicates the file to operate on. For the QFile object created by the first constructor, you need to call the setFileName() method again to indicate the file to operate on.

As with the C++ rules for reading and writing files, you must first open the file before reading and writing files using QFile. You can call the open() member method. The common syntax format is:

bool QFile::open(OpenMode mode)

The mode parameter is used to specify how the file is opened. The following table lists the optional values of this parameter and their respective meanings:

QIODevice::ReadOnly can read files QIODevice::WriteOnly can write files, if the target file does not exist, it will create a new file. QIODevice::ReadWrite is equivalent to ReadOnly| WriteOnly, able to read and write files. QIODevice::Append opens a file in append mode, appending data to the end of the file (the original content of the file is retained). QIODevice::Truncate is turned on in overwrite mode, and the data written will erase all the original data. Note that this opening method cannot be used alone, and is usually paired with ReadOnly or WriteOnly. QIODevice::Text converts the end-of-line character ("\n" on Unix,"\r\n" on Windows) to '\n' when reading a file; converts the end-of-line character to a native format when writing data to a file, such as '\r\n' on Win32 platforms.

Table 1 QFile file opening method

As needed, you can specify multiple values for the mode parameter at once, with values between| Split. For example:

QIODevice::ReadOnly |QIODevice::Text: indicates that only reading operations are allowed on files. When reading files, the end-of-line character will be converted to '\n';

QIODevice::WriteOnly |QIODevice::Text: means that only write operations are allowed to the file. When data is written to the file, the end-of-line character will be converted to the local format;

QIODevice::ReadWrite | QIODevice::Append |QIODevice::Text: indicates that the file is written, the written data will be stored at the end of the file, and the end of the line in the data will be converted to the local format.

Note that multiple values passed to the mode parameter cannot conflict with each other, for example Append and Truncate cannot be used simultaneously.

The open() function returns true if the file was successfully opened, false otherwise.

QFile class provides a lot of functional and practical methods, which can quickly complete the operation of files. The following table lists some commonly used methods:

QFile::size() const Gets the size of the current file. For an open file, this method returns the number of bytes in the file that can be read. bool QIODevice::getChar(char *c) reads a character from a file and stores it in c. The method returns true if the read succeeds, false otherwise. bool QIODevice::putChar(char c) Writes the character c to a file, returns true on success, false otherwise. QByteArray QIODevice::read(qint64 maxSize) Reads maxSize bytes at most from a file at a time and returns the bytes read. qint64 QIODevice::read(char *data, qint64 maxSize) reads maxSize bytes from a file at once, and stores the bytes read into the memory control specified by the data pointer. This method returns the number of bytes successfully read. QByteArray QIODevice::readAll() reads all the data in the file. qint64 QIODevice::readLine(char *data, qint64 maxSize) reads data from a file one line at a time or maxSize-1 bytes at most and stores it in data. This method returns the actual number of bytes read. qint64 QIODevice::write(const char *data, qint64 maxSize) Writes maxSize bytes to data at a time, this method returns the actual number of bytes written. qint64 QIODevice::write(const char *data) Writes data to a file, which returns the number of bytes actually written. qint64 QIODevice::write(const QByteArray &byteArray) Writes bytes stored in byteArray to a file, returning the number of bytes actually written. bool QFile::copy(const QString &newName) Copies the contents of the current file into a file named newName, returning true if successful, false otherwise.

The copy method closes the source file before performing the copy operation. bool QFile::rename(const QString &newName) Renames the current file to newName, returns true on success, false on failure. bool QFile::remove() deletes the current file, returns true on success, false on failure.

Table 2 QFile common methods

Example 1 demonstrates the process of reading and writing text files in QFile class.

#include #include int main(int argc, char *argv[]){ //Create a QFile object and specify the file to manipulate QFile file("D:/demo.txt"); //write to file if(! file.open(QIODevice::WriteOnly|QIODevice::Text)){ qDebug()

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.