C++ Notes: File Operations

Contents

I. Text Files
1.1 Writing to a File
1.2 Reading a File
II. Binary Files
2.1 Writing to a File
2.2 Reading a File

Data generated while a program is running is temporary and is released once the program finishes.

Files can be used to persist data.

File operations in C++ require the #include<fstream> directive.

There are two types of files:

Text files: Files are stored on the computer as ASCII text.
Binary files: Files are stored on the computer in the binary form of text and generally cannot be read directly by users.

File operations:

ofstream: write operations
ifstream: read operations
fstream: read and write operations

I. Text Files

1.1 Writing to a File

The steps for writing to a file are as follows:

Include the header
```
#include<fstream>
```
Create a stream object
```
ofstream ofs;
```

Open the file

ofs.open("文件路径", 打开方式)

Open mode	Explanation
ios::in	Open the file for reading
ios::out	Open the file for writing
ios::ate	Initial position: end of file
ios::app	Write to the file in append mode
ios::trunc	If the file exists, delete it before creating it
ios::binary	Binary mode

File open modes can be combined using the | operator. For example: ios::binary | ios::out

Write data
```
ofs << "写入的数据"
```
Close the file
```
ofs.close
```

1.2 Reading a File

The steps for reading a file are as follows:

Include the header
```
#include<fstream>
```
Create a stream object
```
ifstream ifs;
```

Open the file and check whether it was opened successfully

ifs.open("文件路径", 打开方式)
if(!ifs.is_open()){
    cout << "Error: File open failed." << endl;
    return;
}

Read data

string buf;
while(getline(ifs, buf)){
    cout << buf << endl;
}

Close the file
```
ifs.close();
```

Example:

#include<iostream>
#include<fstream>
#include<string>
using namespace std;

void test(){
	ifstream ifs;
	ifs.open("test.txt", ios::in);
	if(!ifs.is_open()){
		cout << "Error: File open failed." << endl;
		return;
	}
	string buf;
	while(getline(ifs, buf)){
		cout << buf << endl;
	}
	ifs.close();
}

int main(){
	test();
	system("pause");
	return 0;
}

II. Binary Files

Read from and write to files in binary mode.

The open mode must be specified as ios::binary.

2.1 Writing to a File

Writing to a file in binary mode mainly uses the stream object’s write member function.

Function prototype: ostream& write(const char * buffer, int len);

Parameter explanation: The character pointer buffer points to a region of storage in memory. len is the number of bytes read or written.

//例：将Person类中的数据写入文件
#include<iostream>
#include<fstream>
using namespace std;

class Person{
public:
	char m_Name[64];
	int m_Age;
};

void test(){
	ofstream ofs("person.txt",ios::out | ios::binary);
	Person p = {"Huffie", 21};
	ofs.write((const char *)&p, sizeof(Person));
	ofs.close();
}

int main(){
	test();
	system("pause");
	return 0;
}

2.2 Reading a File

Reading a file in binary mode mainly uses the stream object’s read member function.

Function prototype: istream& read(const char * buffer, int len);

//例：读取文件中的数据
#include<iostream>
#include<fstream>
using namespace std;

class Person{
public:
	char m_Name[64];
	int m_Age;
};

void test(){
	ifstream ifs;
	ifs.open("person.txt",ios::in | ios::binary);
	if(!ifs.is_open()){
		cout << "Error: File open failed." << endl;
		return;
	}
	Person p;
	ifs.read((char *)&p, sizeof(Person));
	cout << "Name:" << p.m_Name << endl;
	cout << "Age: " << p.m_Age << endl;
	ifs.close();
}

int main(){

	test();

	system("pause");
	return 0;
}

Reference: Dark Horse Programmer’s Meticulous Work | C++ Tutorial: Start Programming at 0 and Advance to 1, Making Programming Easier to Learn Link: https://www.bilibili.com/video/BV1et411b73Z