How To Make A Text File In Dev C++

I will enter a file name, then the program should add '000' three zeros before the filename, and should create a.txt file. For example if I enter the file name as '1234567' (only digits), It should create 'OP.txt' I can manage to put data on it. Please help me any C experts, I. C program to write and read text in/from file In this program, we will create a file and then write some text into then file, after writing text file will be closed and again file will open in read mode, read all written text.

When you open a file, all kinds of things can go wrong. A file lives on a physical device — a fixed disk, for example, or perhaps on a flash drive or SD card — and you can run into problems when working with physical devices.

For example, part of the disk might be damaged, causing an existing file to become corrupted. Or, less disastrous, you might run out of disk space. Or, even less disastrous, you might try to open a file in a directory that doesn’t exist.

If you try to open a file for writing by specifying a full path and filename but the directory does not exist, the computer responds differently, depending on the operating system you’re using. If you’re unsure how your particular operating system will respond, try writing a simple test application that tries to create and open something like /abc/def/ghi/jkl/abc.txt. (Of course, you’ll want to be sure to use a directory that doesn’t exist.)

Then one of two things will happen: Either the directory and the file will get created, or nothing will happen.

For example, on a Windows system, if we attempt to create a file in a directory that doesn’t exist, the system does not create the directory. That’s because deep down inside, the application ultimately calls an operating system function that does the dirty work of creating the file. And this particular operating system function (it’s called CreateFile(), if you even care) has a rule that it will not create a directory for you.

If you want to determine whether the ostream class was unable to create a file, you can call its fail() member function. This function returns true if the object couldn’t create the file. And that’s what happens when a directory doesn’t exist. The DirectoryCheck01 example shown demonstrates an example of this.

When you run this code, assuming that you don’t have a directory called /abc/def/ghi on your system, you should see the message Couldn’t open the file! Assuming that your particular operating system doesn’t create a directory in this case; if it does, your computer will open the file, write Hi to it, and move on with its happy life after closing things out.

As an alternative to calling the fail() member function, you can use an operator available in various stream classes. This is !, fondly referred to as the “bang” operator, and you would use it in place of calling fail(), as in this code:

Most people prefer to use !outfile instead of outfile.fail(), although !outfile makes confusing code. The reason is that outfile is an object, and the notion of !outfile simply doesn’t make sense.

In fact, !outfile trips up many beginning programmers. They know that outfile is not a pointer in this sample code, and they wonder how you could test it against 0 as you normally can only do with a pointer. (Remember, by saying !x, where x is some pointer, you’re testing x against 0.) And that simply doesn’t make sense! And so, to avoid confusion, just call fail(). It makes more sense.

Here are some reasons your file creation may choke:

  • The directory doesn’t exist.

  • You’re out of disk space and out of luck.

  • Your application doesn’t have the right permissions to create a file.

  • The filename was invalid — that is, it contained characters the operating system doesn’t allow in a filename, such as * or ?.

Like any good application, your application should do two things:

  1. 1.Check whether a file creation succeeded.

  2. 2.If the file creation failed, handle it appropriately.

    Don’t just print a horrible message like Oops!Aborting!, leaving your poor users with no choice but to toss the monitor onto the floor. Instead, do something friendlier — such as presenting a message telling them there’s a problem and suggesting that they might free more disk space.

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This walkthrough shows how to create a traditional Windows desktop application in Visual Studio. The example application you'll create uses the Windows API to display 'Hello, Windows desktop!' in a window. You can use the code that you develop in this walkthrough as a pattern to create other Windows desktop applications.

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The Windows API (also known as the Win32 API, Windows Desktop API, and Windows Classic API) is a C-language-based framework for creating Windows applications. It has been in existence since the 1980s and has been used to create Windows applications for decades. More advanced and easier-to-program frameworks have been built on top of the Windows API. For example, MFC, ATL, the .NET frameworks. Even the most modern Windows Runtime code for UWP and Store apps written in C++/WinRT uses the Windows API underneath. For more information about the Windows API, see Windows API Index. There are many ways to create Windows applications, but the process above was the first.

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Important

For the sake of brevity, some code statements are omitted in the text. The Build the code section at the end of this document shows the complete code.

Prerequisites

  • A computer that runs Microsoft Windows 7 or later versions. We recommend Windows 10 for the best development experience.

  • A copy of Visual Studio. For information on how to download and install Visual Studio, see Install Visual Studio. When you run the installer, make sure that the Desktop development with C++ workload is checked. Don't worry if you didn't install this workload when you installed Visual Studio. You can run the installer again and install it now.

  • An understanding of the basics of using the Visual Studio IDE. If you've used Windows desktop apps before, you can probably keep up. For an introduction, see Visual Studio IDE feature tour.

  • An understanding of enough of the fundamentals of the C++ language to follow along. Don't worry, we don't do anything too complicated.

Create a Windows desktop project

Follow these steps to create your first Windows desktop project. As you go, you'll enter the code for a working Windows desktop application. To see the documentation for your preferred version of Visual Studio, use the Version selector control. It's found at the top of the table of contents on this page.

To create a Windows desktop project in Visual Studio 2019

  1. From the main menu, choose File > New > Project to open the Create a New Project dialog box.

  2. At the top of the dialog, set Language to C++, set Platform to Windows, and set Project type to Desktop.

  3. From the filtered list of project types, choose Windows Desktop Wizard then choose Next. In the next page, enter a name for the project, for example, DesktopApp.

  4. Choose the Create button to create the project.

  5. The Windows Desktop Project dialog now appears. Under Application type, select Desktop application (.exe). Under Additional options, select Empty project. Choose OK to create the project.

  6. In Solution Explorer, right-click the DesktopApp project, choose Add, and then choose New Item.

  7. In the Add New Item dialog box, select C++ File (.cpp). In the Name box, type a name for the file, for example, HelloWindowsDesktop.cpp. Choose Add.

Your project is now created and your source file is opened in the editor. To continue, skip ahead to Create the code.

To create a Windows desktop project in Visual Studio 2017

  1. On the File menu, choose New and then choose Project.

  2. In the New Project dialog box, in the left pane, expand Installed > Visual C++, then select Windows Desktop. In the middle pane, select Windows Desktop Wizard.

    In the Name box, type a name for the project, for example, DesktopApp. Choose OK.

  3. In the Windows Desktop Project dialog, under Application type, select Windows application (.exe). Under Additional options, select Empty project. Make sure Precompiled Header isn't selected. Choose OK to create the project.

  4. In Solution Explorer, right-click the DesktopApp project, choose Add, and then choose New Item.

  5. In the Add New Item dialog box, select C++ File (.cpp). In the Name box, type a name for the file, for example, HelloWindowsDesktop.cpp. Choose Add.

Your project is now created and your source file is opened in the editor. To continue, skip ahead to Create the code.

To create a Windows desktop project in Visual Studio 2015

  1. On the File menu, choose New and then choose Project.

  2. In the New Project dialog box, in the left pane, expand Installed > Templates > Visual C++, and then select Win32. In the middle pane, select Win32 Project.

    In the Name box, type a name for the project, for example, DesktopApp. Choose OK.

  3. On the Overview page of the Win32 Application Wizard, choose Next.

  4. On the Application Settings page, under Application type, select Windows application. Under Additional options, uncheck Precompiled header, then select Empty project. Choose Finish to create the project.

  5. In Solution Explorer, right-click the DesktopApp project, choose Add, and then choose New Item.

  6. In the Add New Item dialog box, select C++ File (.cpp). In the Name box, type a name for the file, for example, HelloWindowsDesktop.cpp. Choose Add.

Your project is now created and your source file is opened in the editor.

Create the code

Next, you'll learn how to create the code for a Windows desktop application in Visual Studio.

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To start a Windows desktop application

  1. Just as every C application and C++ application must have a main function as its starting point, every Windows desktop application must have a WinMain function. WinMain has the following syntax.

    For information about the parameters and return value of this function, see WinMain entry point.

    Note

    What are all those extra words, such as CALLBACK, or HINSTANCE, or _In_? The traditional Windows API uses typedefs and preprocessor macros extensively to abstract away some of the details of types and platform-specific code, such as calling conventions, __declspec declarations, and compiler pragmas. In Visual Studio, you can use the IntelliSense Quick Info feature to see what these typedefs and macros define. Hover your mouse over the word of interest, or select it and press Ctrl+K, Ctrl+I for a small pop-up window that contains the definition. For more information, see Using IntelliSense. Parameters and return types often use SAL Annotations to help you catch programming errors. For more information, see Using SAL Annotations to Reduce C/C++ Code Defects.

  2. Windows desktop programs require <windows.h>. <tchar.h> defines the TCHAR macro, which resolves ultimately to wchar_t if the UNICODE symbol is defined in your project, otherwise it resolves to char. If you always build with UNICODE enabled, you don't need TCHAR and can just use wchar_t directly.

  3. Along with the WinMain function, every Windows desktop application must also have a window-procedure function. This function is typically named WndProc, but you can name it whatever you like. WndProc has the following syntax.

    They have a custom graphical user interface (GUI) with controls copying physical knobs that we find on audio hardware. Massive vst for fl studio 10 free download microsoft.

    In this function, you write code to handle messages that the application receives from Windows when events occur. For example, if a user chooses an OK button in your application, Windows will send a message to you and you can write code inside your WndProc function that does whatever work is appropriate. It's called handling an event. You only handle the events that are relevant for your application.

    For more information, see Window Procedures.

To add functionality to the WinMain function

  1. In the WinMain function, you populate a structure of type WNDCLASSEX. The structure contains information about the window: the application icon, the background color of the window, the name to display in the title bar, among other things. Importantly, it contains a function pointer to your window procedure. The following example shows a typical WNDCLASSEX structure.

    For information about the fields of the structure above, see WNDCLASSEX.

  2. Register the WNDCLASSEX with Windows so that it knows about your window and how to send messages to it. Use the RegisterClassEx function and pass the window class structure as an argument. The _T macro is used because we use the TCHAR type.

  3. Now you can create a window. Use the CreateWindow function.

    This function returns an HWND, which is a handle to a window. A handle is somewhat like a pointer that Windows uses to keep track of open windows. For more information, see Windows Data Types.

  4. At this point, the window has been created, but we still need to tell Windows to make it visible. That's what this code does:

    The displayed window doesn't have much content because you haven't yet implemented the WndProc function. In other words, the application isn't yet handling the messages that Windows is now sending to it.

  5. To handle the messages, we first add a message loop to listen for the messages that Windows sends. When the application receives a message, this loop dispatches it to your WndProc function to be handled. The message loop resembles the following code.

    For more information about the structures and functions in the message loop, see MSG, GetMessage, TranslateMessage, and DispatchMessage.

    At this point, the WinMain function should resemble the following code.

To add functionality to the WndProc function

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  1. To enable the WndProc function to handle the messages that the application receives, implement a switch statement.

    One important message to handle is the WM_PAINT message. The application receives the WM_PAINT message when part of its displayed window must be updated. The event can occur when a user moves a window in front of your window, then moves it away again. Your application doesn't know when these events occur. Only Windows knows, so it notifies your app with a WM_PAINT message. When the window is first displayed, all of it must be updated.

    To handle a WM_PAINT message, first call BeginPaint, then handle all the logic to lay out the text, buttons, and other controls in the window, and then call EndPaint. For the application, the logic between the beginning call and the ending call is to display the string 'Hello, Windows desktop!' in the window. In the following code, notice that the TextOut function is used to display the string.

    HDC in the code is a handle to a device context, which is a data structure that Windows uses to enable your application to communicate with the graphics subsystem. The BeginPaint and EndPaint functions make your application behave like a good citizen and doesn't use the device context for longer than it needs to. The functions help make the graphics subsystem is available for use by other applications.

  2. An application typically handles many other messages. For example, WM_CREATE when a window is first created, and WM_DESTROY when the window is closed. The following code shows a basic but complete WndProc function.

Build the code

As promised, here's the complete code for the working application.

To build this example

  1. Delete any code you've entered in HelloWindowsDesktop.cpp in the editor. Copy this example code and then paste it into HelloWindowsDesktop.cpp:

  2. On the Build menu, choose Build Solution. The results of the compilation should appear in the Output window in Visual Studio.

  3. To run the application, press F5. A window that contains the text 'Hello, Windows desktop!' should appear in the upper-left corner of the display.

Congratulations! You've completed this walkthrough and built a traditional Windows desktop application.

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See also