在 Visual C++ 中执行基本文件 I/O

项目
07/17/2023

本文介绍如何在 Microsoft Visual C++ 或 Visual C++ .NET 中执行基本的文件输入/输出 (I/O) 操作。

原始产品版本： Visual C++
原始 KB 编号： 307398

摘要

如果你不熟悉.NET Framework，你会发现.NET Framework中用于文件操作的对象模型类似于FileSystemObject许多 Visual Studio 开发人员常用的。

若要简化转换，请参阅如何将 FileSystemObject 与 Visual Basic 配合使用。
有关本文的 Visual C# .NET 版本，请参阅如何在 Visual C# 中执行基本文件 I/O。

本文介绍了以下.NET Framework类库命名空间：

System::ComponentModel
System::Windows::Forms
System::Drawing

仍可以在.NET Framework中使用 FileSystemObject 。 FileSystemObject由于是 COM) 组件的组件对象模型 (，因此.NET Framework要求通过互操作层访问对象。如果要使用，.NET Framework会为你生成组件包装器。但是，File.NET Framework中的类、FileInfo类、DirectoryDirectoryInfo类和其他相关类提供的功能在不使用互操作层开销的情况下提供FileSystemObject。

演示的文件 I/O 操作

本文中的示例介绍了基本的文件 I/O 操作。分步示例部分介绍如何创建演示以下六个文件 I/O 操作的示例程序：

读取文本文件
编写文本文件
查看文件信息
列出磁盘驱动器
列出子文件夹
列出文件

读取文本文件

下面的示例代码使用 StreamReader 类来读取文本文件。文件的内容将添加到 ListBox 控件。块 try...catch 用于在文件为空时向程序发出警报。有多种方法可以确定何时到达文件末尾;此示例使用 Peek 方法在阅读前检查下一行。

listBox1->Items->Clear();
try
{
    String* textFile = String::Concat(windir, (S"\\mytest.txt"));
    StreamReader *reader=new  StreamReader(textFile);
    do
    {
        listBox1->Items->Add(reader->ReadLine());
    } while(reader->Peek() != -1);
}

catch (System::Exception *e)
{
    listBox1->Items->Add(e);
}

在 Visual C++ 中，必须添加公共语言运行时支持编译器选项 (/clr：oldSyntax) ，才能成功将以前的代码示例编译为托管 C++。若要添加公共语言运行时支持编译器选项，请执行以下步骤：

单击“ 项目”，然后单击“ <ProjectName> 属性”。

注意

<ProjectName> 是项目名称的占位符。
展开 “配置属性”，然后单击“ 常规”。
在右窗格中，单击以在 公共语言运行时支持项目设置中选择“公共语言运行时支持”、“旧语法 (/clr：oldSyntax) ”。
在“拨号计划(电话上下文)”框中，单击“浏览”以查找用户的拨号计划。

编写文本文件

此示例代码使用 StreamWriter 类创建和写入文件。如果有现有文件，则可以以相同方式打开它。

StreamWriter* pwriter = new StreamWriter(S"c:\\KBTest.txt");
pwriter->WriteLine(S"File created using StreamWriter class.");
pwriter->Close();
listBox1->Items->Clear();
String *filew = new String(S"File Written to C:\\KBTest.txt");
listBox1->Items->Add(filew);

查看文件信息

此示例代码使用 FileInfo 类访问文件的属性。此示例使用 Notepad.exe。属性显示在 ListBox 控件中。

listBox1->Items->Clear();
String* testfile = String::Concat(windir, (S"\\notepad.exe"));
FileInfo *pFileProps =new FileInfo(testfile);

listBox1->Items->Add(String::Concat(S"File Name = ", (pFileProps->get_FullName())));
listBox1->Items->Add(String::Concat(S"Creation Time = ", (pFileProps->get_CreationTime()).ToString()));
listBox1->Items->Add(String::Concat(S"Last Access Time = " ,(pFileProps->get_LastAccessTime()).ToString()));
listBox1->Items->Add(String::Concat(S"Last Write Time = ", (pFileProps->get_LastWriteTime()).ToString()));
listBox1->Items->Add(String::Concat(S"Size = ", (pFileProps->get_Length()).ToString()));

列出磁盘驱动器

此示例代码使用 Directory 和 Drive 类列出系统上的逻辑驱动器。对于此示例，结果显示在 ListBox 控件中。

listBox1->Items->Clear();
String* drives[] = Directory::GetLogicalDrives();
int numDrives = drives->get_Length();
for (int i=0; i<numDrives; i++)
{
    listBox1->Items->Add(drives[i]);
}

列出子文件夹

此示例代码使用 GetDirectories 类的 Directory 方法来获取文件夹列表。

listBox1->Items->Clear();
String* dirs[] = Directory::GetDirectories(windir);
int numDirs = dirs->get_Length();
for (int i=0; i<numDirs; i++)
{
    listBox1->Items->Add(dirs[i]);
}

列出文件

此示例代码使用 GetFiles 类的 Directory 方法获取文件列表。

listBox1->Items->Clear();
String* files[]= Directory::GetFiles(this->windir);
int numFiles = files->get_Length();
for (int i=0; i<numFiles; i++)
{
    listBox1->Items->Add(files[i]);
}

当用户获得对文件的访问权限时，许多事情都可能会出错。这些文件可能不存在，文件可能正在使用，或者用户可能没有权限访问他们尝试访问的文件夹的文件。编写代码来处理可能生成的异常时，请考虑这些可能性。

分步示例

启动 Visual Studio .NET。
在"文件"菜单上，指向"新建"，然后单击"项目"。
在“ 项目类型”下，单击“ Visual C++ 项目”。在“模板”部分下，单击“Windows 窗体应用程序” (.NET) 。
在“名称”框中键入KB307398，C:\在“位置”框中键入，然后单击“确定”。
在“设计”视图中打开 Form1 窗体，然后按 F4 打开 “属性” 窗口。
在 “属性” 窗口中，展开 “大小” 文件夹。在“ 宽度 ”框中，键入 700。在“ 高度 ”框中，键入 320。
向 Form1 添加一个 ListBox 控件和六个按钮控件。

注意

若要查看工具箱，请单击“视图”菜单上的“工具箱”。

在 “属性” 窗口中，更改这些控件的 Location、 Name、 Size、 TabIndex 和 Text 属性，如下所示：

控件 ID	位置	名称	Size	TabIndex	Text
button1	500, 32	button1	112, 23	1	读取文本文件
button2	500, 64	button2	112, 23	2	写入文本文件
button3	500, 96	button3	112, 23	3	查看文件信息
button4	500, 128	button4	112, 23	4	列出驱动器
button5	500, 160	button5	112, 23	5	列出子文件夹
button6	500, 192	button6	112, 23	6	列出文件
listBox1	24, 24	listBox1	450, 200	0	listBox1

打开 Form1.h 文件。在 Form1 类声明中，使用以下代码声明一个私有 String 变量：
```
private:
String *windir;
```

在 Form1 类构造函数中，添加以下代码：

windir = System::Environment::GetEnvironmentVariable("windir");

若要执行文件输入输出操作，请 System::IO 添加命名空间。

按 SHIFT+F7 在“设计”视图中打开 Form1 。双击“ 读取文本文件 ”按钮，然后粘贴以下代码：

// How to read a text file:
// Use try...catch to deal with a 0 byte file or a non-existant file.
listBox1->Items->Clear();

try
{
    String* textFile = String::Concat(windir, (S"\\mytest.txt"));
    StreamReader *reader=new  StreamReader(textFile);
    do
    {
        listBox1->Items->Add(reader->ReadLine());
    } while(reader->Peek() != -1);
}
catch(FileNotFoundException *ex)
{
    listBox1->Items->Add(ex);
}  

catch (System::Exception *e)
{
    listBox1->Items->Add(e);
}

在“Form1 设计”视图中，双击“ 写入文本文件” 按钮，然后粘贴以下代码：

// This demonstrates how to create and to write to a text file.
StreamWriter* pwriter = new StreamWriter(S"c:\\KBTest.txt");
pwriter->WriteLine(S"The file was created by using the StreamWriter class.");
pwriter->Close();
listBox1->Items->Clear();
String *filew = new String(S"File written to C:\\KBTest.txt");
listBox1->Items->Add(filew);

在“Form1 设计”视图中，双击“ 查看文件信息 ”按钮，然后将以下代码粘贴到方法中：

// This code retrieves file properties. The example uses Notepad.exe.
listBox1->Items->Clear();
String* testfile = String::Concat(windir, (S"\\notepad.exe"));
FileInfo *pFileProps =new FileInfo(testfile);

listBox1->Items->Add(String::Concat(S"File Name = ", (pFileProps->get_FullName())));
listBox1->Items->Add(String::Concat(S"Creation Time = ", (pFileProps->get_CreationTime()).ToString()));
listBox1->Items->Add(String::Concat(S"Last Access Time = " ,(pFileProps->get_LastAccessTime()).ToString()));
listBox1->Items->Add(String::Concat(S"Last Write Time = ", (pFileProps->get_LastWriteTime()).ToString()));
listBox1->Items->Add(String::Concat(S"Size = ", (pFileProps->get_Length()).ToString()));

在“Form1 设计”视图中，双击“列出驱动器”按钮，然后粘贴以下代码：

// This demonstrates how to obtain a list of disk drives.
listBox1->Items->Clear();
String* drives[] = Directory::GetLogicalDrives();
int numDrives = drives->get_Length();
for (int i=0; i<numDrives; i++)
{
    listBox1->Items->Add(drives[i]);
}

在“Form1 设计”视图中，双击“列出子文件夹”按钮，然后粘贴以下代码：

// This code obtains a list of folders. This example uses the Windows folder.
listBox1->Items->Clear();
String* dirs[] = Directory::GetDirectories(windir);
int numDirs = dirs->get_Length();
for (int i=0; i<numDirs; i++)
{
    listBox1->Items->Add(dirs[i]);
}

在“Form1 设计”视图中，双击“列出文件”按钮，然后粘贴以下代码：

// This code obtains a list of files. This example uses the Windows folder.
listBox1->Items->Clear();
String* files[]= Directory::GetFiles(this->windir);
int numFiles = files->get_Length();
for (int i=0; i<numFiles; i++)
{
    listBox1->Items->Add(files[i]);
}

若要生成并运行程序，请按 Ctrl+F5。

完整代码示例

//Form1.h
#pragma once

namespace KB307398
{
    using namespace System;
    using namespace System::IO;
    using namespace System::ComponentModel;
    using namespace System::Collections;
    using namespace System::Windows::Forms;
    using namespace System::Data;
    using namespace System::Drawing;

    /// <summary>
    /// Summary for Form1
    /// WARNING: If you change the name of this class, you will need to change the
    ///          'Resource File Name' property for the managed resource compiler tool
    ///          associated with all .resx files this class depends on.  Otherwise,
    ///          the designers will not be able to interact properly with localized
    ///          resources associated with this form.
    /// </summary>
    public __gc class Form1 : public System::Windows::Forms::Form
    {
        private:
        String *windir;
        public:
        Form1(void)
        {
            windir = System::Environment::GetEnvironmentVariable("windir");
            InitializeComponent();
        }

        protected:
        void Dispose(Boolean disposing)
        {
            if (disposing && components)
            {
            components->Dispose();
            }
            __super::Dispose(disposing);
        }
        private: System::Windows::Forms::Button *  button1;
        private: System::Windows::Forms::Button *  button2;
        private: System::Windows::Forms::Button *  button3;
        private: System::Windows::Forms::Button *  button4;
        private: System::Windows::Forms::Button *  button5;
        private: System::Windows::Forms::Button *  button6;
        private: System::Windows::Forms::ListBox *  listBox1;

        private:
        /// <summary>
        /// Required designer variable.
        /// </summary>
        System::ComponentModel::Container * components;

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        void InitializeComponent(void)
        {
            this->button1 = new System::Windows::Forms::Button();
            this->button2 = new System::Windows::Forms::Button();
            this->button3 = new System::Windows::Forms::Button();
            this->button4 = new System::Windows::Forms::Button();
            this->button5 = new System::Windows::Forms::Button();
            this->button6 = new System::Windows::Forms::Button();
            this->listBox1 = new System::Windows::Forms::ListBox();
            this->SuspendLayout();
            // button1
            this->button1->Location = System::Drawing::Point(500, 32);
            this->button1->Name = S"button1";
            this->button1->Size = System::Drawing::Size(112, 23);
            this->button1->TabIndex = 1;
            this->button1->Text = S"Read Text File";
            this->button1->Click += new System::EventHandler(this, button1_Click);
            // button2
            this->button2->Location = System::Drawing::Point(500, 64);
            this->button2->Name = S"button2";
            this->button2->Size = System::Drawing::Size(112, 23);
            this->button2->TabIndex = 2;
            this->button2->Text = S"Write Text File";
            this->button2->Click += new System::EventHandler(this, button2_Click);
            // button3
            this->button3->Location = System::Drawing::Point(500, 96);
            this->button3->Name = S"button3";
            this->button3->Size = System::Drawing::Size(112, 23);
            this->button3->TabIndex = 3;
            this->button3->Text = S"View File Information";
            this->button3->Click += new System::EventHandler(this, button3_Click);
            // button4
            this->button4->Location = System::Drawing::Point(500, 128);
            this->button4->Name = S"button4";
            this->button4->Size = System::Drawing::Size(112, 23);
            this->button4->TabIndex = 4;
            this->button4->Text = S"List Drives";
            this->button4->Click += new System::EventHandler(this, button4_Click);
            // button5
            this->button5->Location = System::Drawing::Point(500, 160);
            this->button5->Name = S"button5";
            this->button5->Size = System::Drawing::Size(112, 23);
            this->button5->TabIndex = 5;
            this->button5->Text = S"List Subfolders";
            this->button5->Click += new System::EventHandler(this, button5_Click);
            // button6
            this->button6->Location = System::Drawing::Point(500, 188);
            this->button6->Name = S"button6";
            this->button6->Size = System::Drawing::Size(112, 23);
            this->button6->TabIndex = 6;
            this->button6->Text = S"List Files";
            this->button6->Click += new System::EventHandler(this, button6_Click);
            // listBox1
            this->listBox1->Location = System::Drawing::Point(24, 24);
            this->listBox1->Name = S"listBox1";
            this->listBox1->Size = System::Drawing::Size(450, 199);
            this->listBox1->TabIndex = 0;
            // Form1
            this->AutoScaleBaseSize = System::Drawing::Size(5, 13);
            this->ClientSize = System::Drawing::Size(692, 293);
            this->Controls->Add(this->listBox1);
            this->Controls->Add(this->button6);
            this->Controls->Add(this->button5);
            this->Controls->Add(this->button4);
            this->Controls->Add(this->button3);
            this->Controls->Add(this->button2);
            this->Controls->Add(this->button1);
            this->Name = S"Form1";
            this->Text = S"Form1";
            this->ResumeLayout(false);
        }
        private: System::Void button1_Click(System::Object *  sender, System::EventArgs *  e)
        {
            // This code shows how to read a text file.
            // The try...catch code is to deal with a 0 byte file or a non-existant file.
            listBox1->Items->Clear();

            try
            {
                String* textFile = String::Concat(windir, (S"\\mytest.txt"));
                StreamReader *reader=new  StreamReader(textFile);
                do
                {
                    listBox1->Items->Add(reader->ReadLine());
                }
                while(reader->Peek() != -1);
            }
            catch(FileNotFoundException *ex)
            {
                listBox1->Items->Add(ex);
            }

            catch (System::Exception *e)
            {
                listBox1->Items->Add(e);
            }
        }

        private: System::Void button2_Click(System::Object *  sender, System::EventArgs *  e)
        {
            // This code demonstrates how to create and to write to a text file.
            StreamWriter* pwriter = new StreamWriter(S"c:\\KBTest.txt");
            pwriter->WriteLine(S"The file was created by using the StreamWriter class.");
            pwriter->Close();
            listBox1->Items->Clear();
            String *filew = new String(S"The file was written to C:\\KBTest.txt");
            listBox1->Items->Add(filew);
        }

        private: System::Void button3_Click(System::Object *  sender, System::EventArgs *  e)
         {
            // This code retrieves file properties. This example uses Notepad.exe.
            listBox1->Items->Clear();
            String* testfile = String::Concat(windir, (S"\\notepad.exe"));
            FileInfo *pFileProps  =new FileInfo(testfile);

            listBox1->Items->Add(String::Concat(S"File Name = ", (pFileProps->get_FullName() )) );
            listBox1->Items->Add(String::Concat(S"Creation Time = ", (pFileProps->get_CreationTime() ).ToString()) );
            listBox1->Items->Add(String::Concat(S"Last Access Time = "  ,(pFileProps->get_LastAccessTime() ).ToString()) );
            listBox1->Items->Add(String::Concat(S"Last Write Time = ", (pFileProps->get_LastWriteTime() ).ToString()) );
            listBox1->Items->Add(String::Concat(S"Size = ", (pFileProps->get_Length() ).ToString()) );
        }

        private: System::Void button4_Click(System::Object *  sender, System::EventArgs *  e)
        {
            // The code demonstrates how to obtain a list of disk drives.
            listBox1->Items->Clear();
            String* drives[] = Directory::GetLogicalDrives();
            int numDrives = drives->get_Length();
            for (int i=0; i<numDrives; i++)
            {
                listBox1->Items->Add(drives[i]);
            }
        }

        private: System::Void button5_Click(System::Object *  sender, System::EventArgs *  e)
        {
            // This code obtains a list of folders. This example uses the Windows folder.
            listBox1->Items->Clear();
            String* dirs[] = Directory::GetDirectories(windir);
            int numDirs = dirs->get_Length();
            for (int i=0; i<numDirs; i++)
            {
                listBox1->Items->Add(dirs[i]);
            }
        }

        private: System::Void button6_Click(System::Object *  sender, System::EventArgs *  e)
        {
            // This code obtains a list of files. This example uses the Windows folder.
            listBox1->Items->Clear();
            String* files[]= Directory::GetFiles(this->windir);
            int numFiles = files->get_Length();
            for (int i=0; i<numFiles; i++)
            {
                listBox1->Items->Add(files[i]);
            }
        }
    };
}

//Form1.cpp
#include "stdafx.h"
#include "Form1.h"
#include <windows.h>

using namespace KB307398;

int APIENTRY _tWinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,
                     int       nCmdShow)
{
    System::Threading::Thread::CurrentThread->ApartmentState = System::Threading::ApartmentState::STA;
    Application::Run(new Form1());
    return 0;
}

References

有关详细信息，请访问 Microsoft 支持部门。有关如何在 C++ 的托管扩展中创建 Windows 窗体的详细信息，请参阅 ManagedCWinFormWiz Visual Studio .NET 帮助中的示例。