File functions to quickly read and write files

Documents are an integral part of our daily work and life. File functions are key tools for handling file operations and can help us quickly read and write file contents. In this article, we will introduce how to use file functions to improve work efficiency and convenience.

1. Overview of file functions

File functions are a set of functions used to process file operations. These functions can be used to read, write and manage various types of files. document. In most programming languages, standard file function libraries are provided, such as C's standard file library, Python's IO module, etc. These function libraries provide a variety of functions that can be called directly, greatly reducing the difficulty of encapsulating our code. .

File functions usually include the following categories:

1. Open and close files: These functions are used to open and close files for subsequent read and write operations.
2. Reading and writing file contents: These functions can read and write the contents of files.
3. File positioning: These functions are used to locate the file pointer position in order to continue reading and writing the file content.
4. File status query: These functions are used to query the status of the file, such as whether the file exists, file size and other information.

2. Specific use of file functions

Before using file functions, we need to understand several important concepts.

File pointer: The file pointer is a pointer to the internal location of the file. It is used to maintain the current read or write location. In most cases, we can use the default pointer provided by the system. When we use file functions to read and write files, the pointer will automatically increment and point to the next location that can be read or written.

File opening methods: The file function provides several ways to open files, including read-only, write-only and read-write. When opening a file, we need to use an appropriate method to determine the type of operation we want to achieve.

The following is a simple case to help us better understand how to use file functions.

Case: Reading student information from a file

Suppose we are writing a program to read student information from a file. Assume that each row contains a student's information, including name and grades, in the format of "name:grade", such as "Zhang San:90".

First, we need to open the file. In C, we can use the fstream library to manipulate files. The following is an example of opening a file:

#include <fstream>
using namespace std;

int main()
{
    fstream file("students.txt", ios::in); //打开students.txt文件，只读方式
    if(!file)  // 如果打开文件失败
    {
        cout << "文件打开失败" << endl;
        return -1; 
    }
    // 读取文件内容...

    file.close(); // 关闭文件
    return 0; 
}

In the above code, we use the fstream class in the fstream library to open the file, where "students.txt" represents the file name and ios::in represents only Open in read mode. If opening the file fails, a prompt message will be output and the program will exit; otherwise, we can continue to read and write the file.

Then, we need to read each line in the file and save the student information into a two-dimensional character array. The following is an example of reading a file and storing student information:

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

int main()
{
    fstream file("students.txt", ios::in); // 打开students.txt文件，只读方式
    if(!file)  // 如果打开文件失败
    {
        cout << "文件打开失败" << endl;
        return -1; 
    }

    string line; // 定义一个变量用于存储每行读取的内容
    string student[100][2]; // 定义数组用于存储学生信息

    int i = 0;
    while (getline(file, line)) // 逐行读取文件内容
    {
        int pos = line.find(":"); // find函数用于查找给定字符（‘：’）的位置
        if(pos != -1)
        {
            student[i][0] = line.substr(0, pos);  // substr函数用于截取子字符串
            student[i][1] = line.substr(pos + 1);
            i++;
        }
    }

    file.close(); // 关闭文件

    // 输出读取的学生信息
    for(int j = 0; j < i; j++)
    {
        cout << "姓名：" << student[j][0] << "，成绩：" << student[j][1] << endl;
    }

    return 0; 
}

In the above code, we use the getline function to read the file content line by line, and use the substr function to intercept the student name in each line and grades. Finally, we save the read student information into the student array and output the name and grades of each student.

Finally, we need to write some data to the file. The following is an example of writing a file:

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

int main()
{
    fstream file("students.txt", ios::out); // 打开students.txt文件，只写方式
    if(!file)  // 如果打开文件失败
    {
        cout << "文件打开失败" << endl;
        return -1; 
    }

    string student[2][2] = {
        {"张三", "90"},
        {"李四", "80"}
    }; // 定义学生信息

    // 将学生信息写入文件
    for(int i = 0; i < 2; i++)
    {
        file << student[i][0] << ":" << student[i][1] << endl;
    }

    file.close(); // 关闭文件

    return 0; 
}

In the above code, we use the ofstream class to open the file, ios:: out means opening the file for writing only. Then, we use a for loop to write the student information to the file one by one, and add a carriage return symbol at the end of each line. Finally, we close the file after the program has finished executing.

3. Limitations of file functions

File functions are necessary tools for processing file operations, but they also have some limitations. The following are some common limitations:

1. File size limitations: File functions may be limited by file size when reading and writing files. If when reading and writing a file, the file is too large to be read or written into memory at once, you need to read and write in segments.
2. Binary file processing issues: File functions are usually used to process text files. However, working with binary files requires the use of special functions and techniques.
3. File sharing problems: When reading and writing the same file in multiple programs at the same time, it may cause file sharing problems and conflicts.

To sum up, file functions are very useful when dealing with file operations. However, when using the file function, we need to pay attention to its limitations to avoid unnecessary problems.

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