C++ error: The input and output stream object is not opened, how to solve it?

C is a high-level programming language widely used in software development. It is often used to develop system software, application software, games and other types of software. In the process of writing programs in C, we often encounter some errors, including errors that the input and output stream objects are not opened. This article will introduce the reasons and solutions for the input and output stream objects not being opened.

1. Error message

When we use the input and output stream object in the program, if we do not successfully open the corresponding input and output file stream, the following error message will appear:

输入输出流对象未打开

2. Cause of the error

1. The file does not exist or the path is wrong

When we open the file, if the file does not exist or the path is wrong, it cannot be opened. file stream, resulting in an error that the input and output stream objects are not opened.

2. File opening mode error

When opening a file stream, we need to specify the corresponding file opening mode (such as read-only, write-only, read-write, etc.). If we choose the wrong opening method, it will also cause an error that the input and output stream objects are not opened.

3. Read and write location error

For file streams, we need to specify the read and write location when reading and writing files. If the read and write location is specified incorrectly, it will also result in an error that the input and output stream object is not opened.

3. Solution

1. Check the file path

When we encounter an error that the input and output stream object is not opened, we must first check the file path correct and make sure the file exists. If the file does not exist or the file path is wrong, we need to reset the file path.

2. Check the file opening method

For file streams, we need to specify the corresponding file opening method. If we choose the wrong opening method, it will result in an error that the input and output stream objects are not opened. We need to confirm whether the selected file is opened correctly.

Normally, we can set the file opening mode to "r" (read-only) or "w" (write-only), etc.

3. Check the read and write location

For file streams, we need to specify the read and write location when reading and writing files. If the read and write location is specified incorrectly, it will also result in an error that the input and output stream object is not opened. We need to confirm that the read and write locations are set correctly.

4. Sample Code

The following code demonstrates how to use C's input and output streams to operate files and avoid errors that the input and output stream objects are not opened. Here we open the file in read-only mode and read the contents of the file and output them to the screen.

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

int main() {
    string filename = "example.txt";         // 文件路径
    ifstream infile;                         // 输入流对象

    infile.open(filename, ios::in);          // 打开文件
    if (!infile.is_open()) {                  // 检查是否打开成功
        cout << "无法打开文件！" << endl;
        return 0;                            // 返回主函数
    }

    string line;
    while (getline(infile, line)) {          // 逐行读取内容
        cout << line << endl;                // 输出
    }

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

In the above code, we use C's ifstream object to open the example.txt file, and use a while loop to read the contents of the file line by line and output it to the screen. At the end of the main function, we close the file.

5. Summary

When we encounter an error that the input and output stream objects are not opened when writing a program in C, we need to check whether the file path, file opening method, and read and write location are set correctly. . Only by setting these parameters correctly can we successfully open the file stream and read and write the file content, thereby avoiding errors that the input and output stream objects are not opened.

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