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This article shows you the detailed usage of C++ ofstream and ifstream. The content is concise and easy to understand. It will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

First, the two important operators of the stream class 1, the inserter (x;) means to read a specified type of data from the standard input stream.

In C++, the manipulation of files is achieved through the subclass fstream (file stream) of stream, so to manipulate files in this way, you must add the header file fstream.h.

Second, common file operations 1. Open files

In the fstream class, there is a member function open (), which is used to open a file, and its prototype is:

Void open (const char* filename,int mode,int access)

Parameters:

Filename: name of the file to open

Mode: how you want to open a file

Access: properties of the open file

The way to open a file is defined in the class ios, which is the base class for all streaming Imax O classes.

Common values are as follows:

Ios::app: open a file as an append

Ios::ate: navigate to the end of the file after the file is opened, and ios:app contains this attribute

Ios::binary: open the file in binary mode, which is text by default. For the difference between the two ways, see above.

Ios::in: file opening as input (file data input to memory)

Ios::out: file is opened as output (memory data is exported to file)

Ios::nocreate: no file is created, so it fails to open if the file does not exist.

Ios::noreplace: do not overwrite the file, so if the file exists failure when opening the file

Ios::trunc: if the file exists, set the file length to 0

You can connect the above attributes with "or", such as ios::out | ios::binary

The values for the properties of the open file are:

0: normal file, open and access

1: read-only fil

2: implied file

4: system Fil

You can connect the above attributes with "or" or "+", such as 3 or 1 | 2 to open the file with read-only and implicit attributes.

For example:

Open the file c:\ config.sys as binary input

Fstream file1

File1.open ("c:\\ config.sys", ios::binary | ios::in,0)

If the open function has only one argument to the file name, it opens as a read / write normal file, that is:

File1.open ("c:\\ config.sys"); file1.open ("c:\\ config.sys", ios::in | ios::out,0)

In addition, fstream has the same constructor as open (). For the above example, you can open the file when it is defined:

Fstream file1 ("c:\\ config.sys");

In particular, fstream has two subclasses:

Ifstream (input file stream) and ofstream (outpu file stream)

Ifstream opens the file as input by default

Ofstream opens the file as output by default.

Ifstream file2 ("c:\\ pdos.def"); / / Open the file ofstream file3 ("c:\\ x.123") as input; / / Open the file as output

Therefore, in the practical application, according to the different needs, choose different classes to define:

If you want to open it as input, use ifstream to define it.

If you want to open it as output, use ofstream to define it.

If you want to open it as input / output, use fstream to define it.

2. Close the file

Open files must be closed after use. Fstream provides a member function close () to complete this operation.

Such as: file1.close ()

Close the files connected to file1.

3. Read and write files

Read and write files are divided into text files and binary files.

It is easy to read a text file, just use an inserter and a parser

It is more complicated to read binary, so we will introduce these two methods in detail.

(1) Reading and writing of text files:

Use the inserter () to import from the file.

Suppose file1 is opened as input and file2 as output.

Examples are as follows:

File2i;// enters an integer value from the file.

This method also has a simple formatting ability, for example, you can specify the output to hexadecimal, and so on, the specific formats are as follows

Manipulator function input / output

Dec formatted as decimal numerical data input and output

Endl outputs a newline character and refreshes the stream output

Ends output an empty character output

Hex formatted as hexadecimal numeric data input and output

Oct formatted as octal numeric data input and output

Setpxecision (int p) sets the precision digit output of floating-point numbers

Example:

# include # include using namespace std;void main (void) {/ / use the constructor of the ofstream class to create a file output stream object to open the file ofstream fout ("d:\\ mytest.txt"); if (! Fout) {cout

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