From f9f77578f6bc2a4803ac4ea0a5cb180de8266331 Mon Sep 17 00:00:00 2001 From: wyxplus <32919297+wyxplus@users.noreply.github.com> Date: Wed, 31 Mar 2021 11:07:33 +0800 Subject: [PATCH 1/3] =?UTF-8?q?=E6=8F=90=E4=BA=A4=E7=BF=BB=E8=AF=91?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ...210326 How to read and write files in C.md | 144 ------------------ ...210326 How to read and write files in C.md | 141 +++++++++++++++++ 2 files changed, 141 insertions(+), 144 deletions(-) delete mode 100644 sources/tech/20210326 How to read and write files in C.md create mode 100644 translated/tech/20210326 How to read and write files in C.md diff --git a/sources/tech/20210326 How to read and write files in C.md b/sources/tech/20210326 How to read and write files in C.md deleted file mode 100644 index 8fe721461e..0000000000 --- a/sources/tech/20210326 How to read and write files in C.md +++ /dev/null @@ -1,144 +0,0 @@ -[#]: subject: (How to read and write files in C++) -[#]: via: (https://opensource.com/article/21/3/ccc-input-output) -[#]: author: (Stephan Avenwedde https://opensource.com/users/hansic99) -[#]: collector: (lujun9972) -[#]: translator: (wyxplus) -[#]: reviewer: ( ) -[#]: publisher: ( ) -[#]: url: ( ) - -How to read and write files in C++ -====== -If you know how to use I/O streams in C++, you can (in principle) handle -any kind of I/O device. -![Computer screen with files or windows open][1] - -In C++, reading and writing to files can be done by using I/O streams in conjunction with the stream operators `>>` and `<<`. When reading or writing to files, those operators are applied to an instance of a class representing a file on the hard drive. This stream-based approach has a huge advantage: From a C ++ perspective, it doesn't matter what you are reading or writing to, whether it's a file, a database, the console, or another PC you are connected to over the network. Therefore, knowing how to write files using stream operators can be transferred to other areas. - -### I/O stream classes - -The C++ standard library provides the class [ios_base][2]. This class acts as the base class for all I/O stream-compatible classes, such as [basic_ofstream][3] and [basic_ifstream][4]. This example will use the specialized types for reading/writing characters, `ifstream` and `ofstream`. - - * `ofstream` means _output file stream_, and it can be accessed with the insertion operator, `<<`. - * `ifstream` means _input file stream_, and it can be accessed with the extraction operator, `>>`. - - - -Both types are defined inside the header ``. - -A class that inherits from `ios_base` can be thought of as a data sink when writing to it or as a data source when reading from it, completely detached from the data itself. This object-oriented approach makes concepts such as [separation of concerns][5] and [dependency injection][6] easy to implement. - -### A simple example - -This example program is quite simple: It creates an `ofstream`, writes to it, creates an `ifstream`, and reads from it: - - -``` -#include <iostream> // cout, cin, cerr etc... -#include <fstream> // ifstream, ofstream -#include <string> - -int main() -{ -    std::string sFilename = "MyFile.txt";     - -    /****************************************** -     *                                        * -     *                WRITING                 * -     *                                        * -     ******************************************/ - -    std::ofstream fileSink(sFilename); // Creates an output file stream - -    if (!fileSink) { -        std::cerr << "Canot open " << sFilename << std::endl; -        exit(-1); -    } - -    /* std::endl will automatically append the correct EOL */ -    fileSink << "Hello Open Source World!" << std::endl; - -    /****************************************** -     *                                        * -     *                READING                 * -     *                                        * -     ******************************************/ -    -    std::ifstream fileSource(sFilename); // Creates an input file stream - -    if (!fileSource) { -        std::cerr << "Canot open " << sFilename << std::endl; -        exit(-1); -    } -    else { -        // Intermediate buffer -        std::string buffer; - -        // By default, the >> operator reads word by workd (till whitespace) -        while (fileSource >> buffer) -        { -            std::cout << buffer << std::endl; -        } -    } - -    exit(0); -} -``` - -This code is available on [GitHub][7]. When you compile and execute it, you should get the following output: - -![Console screenshot][8] - -(Stephan Avenwedde, [CC BY-SA 4.0][9]) - -This is a simplified, beginner-friendly example. If you want to use this code in your own application, please note the following: - - * The file streams are automatically closed at the end of the program. If you want to proceed with the execution, you should close them manually by calling the `close()` method. - * These file stream classes inherit (over several levels) from [basic_ios][10], which overloads the `!` operator. This lets you implement a simple check if you can access the stream. On [cppreference.com][11], you can find an overview of when this check will (and won't) succeed, and you can implement further error handling. - * By default, `ifstream` stops at white space and skips it. To read line by line until you reach [EOF][12], use the `getline(...)`-method. - * For reading and writing binary files, pass the `std::ios::binary` flag to the constructor: This prevents [EOL][13] characters from being appended to each line. - - - -### Writing from the systems perspective - -When writing files, the data is written to the system's in-memory write buffer. When the system receives the system call [sync][14], this buffer's contents are written to the hard drive. This mechanism is also the reason you shouldn't remove a USB stick without telling the system. Usually, _sync_ is called on a regular basis by a daemon. If you really want to be on the safe side, you can also call _sync_ manually: - - -``` -#include <unistd.h> // needs to be included - -sync(); -``` - -### Summary - -Reading and writing to files in C++ is not that complicated. Moreover, if you know how to deal with I/O streams, you also know (in principle) how to deal with any kind of I/O device. Libraries for various kinds of I/O devices let you use stream operators for easy access. This is why it is beneficial to know how I/O steams work. - --------------------------------------------------------------------------------- - -via: https://opensource.com/article/21/3/ccc-input-output - -作者：[Stephan Avenwedde][a] -选题：[lujun9972][b] -译者：[译者ID](https://github.com/译者ID) -校对：[校对者ID](https://github.com/校对者ID) - -本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 - -[a]: https://opensource.com/users/hansic99 -[b]: https://github.com/lujun9972 -[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/browser_screen_windows_files.png?itok=kLTeQUbY (Computer screen with files or windows open) -[2]: https://en.cppreference.com/w/cpp/io/ios_base -[3]: https://en.cppreference.com/w/cpp/io/basic_ofstream -[4]: https://en.cppreference.com/w/cpp/io/basic_ifstream -[5]: https://en.wikipedia.org/wiki/Separation_of_concerns -[6]: https://en.wikipedia.org/wiki/Dependency_injection -[7]: https://github.com/hANSIc99/cpp_input_output -[8]: https://opensource.com/sites/default/files/uploads/c_console_screenshot.png (Console screenshot) -[9]: https://creativecommons.org/licenses/by-sa/4.0/ -[10]: https://en.cppreference.com/w/cpp/io/basic_ios -[11]: https://en.cppreference.com/w/cpp/io/basic_ios/operator! -[12]: https://en.wikipedia.org/wiki/End-of-file -[13]: https://en.wikipedia.org/wiki/Newline -[14]: https://en.wikipedia.org/wiki/Sync_%28Unix%29 diff --git a/translated/tech/20210326 How to read and write files in C.md b/translated/tech/20210326 How to read and write files in C.md new file mode 100644 index 0000000000..67d7b6c583 --- /dev/null +++ b/translated/tech/20210326 How to read and write files in C.md @@ -0,0 +1,141 @@ +[#]: subject: (How to read and write files in C++) +[#]: via: (https://opensource.com/article/21/3/ccc-input-output) +[#]: author: (Stephan Avenwedde https://opensource.com/users/hansic99) +[#]: collector: (lujun9972) +[#]: translator: (wyxplus) +[#]: reviewer: ( ) +[#]: publisher: ( ) +[#]: url: ( ) + +如何用 C++ 读写文件 +====== + +如果你知道如何在 C++ 中使用输入输出I/O输入输出I/O流，那么你便能够（原则上）处理任何类型的输入输出设备。 + +![Computer screen with files or windows open][1] + +在 C++ 中，可以通过将输入输出流与流运算符 `>>` 和 `<<` 结合使用来进行文件读写。当读写文件的时候，这些运算符将应用于代表硬盘驱动器上文件类的实例上。这种基于流的方法有个巨大的优势：从 C++ 的角度，无论你要读取或写入的内容是文件、数据库、控制台，亦或是你通过网络连接的另外一台电脑，这都无关紧要。因此，知道如何使用流运算符来写入文件能够被利用到其他领域。 + +### 输入输出流类 + +C++ 标准库提供了 [ios_base][2] 类。该类充当所有 I/O 流的基类，例如 [basic_ofstream][3] 和 [basic_ifstream][4]。本例将使用特殊的类型来读写字符，`ifstream` 和 `ofstream`。 + +- `ofstream`：输出文件流，并且其能通过插入运算符 `<<` 来实现。 +- `ifstream`：输入文件流，并且其能通过提取运算符 `>>` 来实现。 + +该两种类型都是在头文件 `` 中所定义。 + +从 `ios_base` 继承的类在写入时可被视为数据接收器，在从其读取时可被视为数据源，与数据本身完全分离。这种面向对象的方法使 [关注点分离][5]separation of concerns[关注点分离][5]separation of concerns 和 [依赖注入][6]dependency injection[依赖注入][6]dependency injection 等概念易于实现。 + +### A simple example 一个简单的例子 + +本例程是非常简单：实例化了一个 `ofstream` 来写入，和实例化一个 `ifstream` 来读取。 + + +``` +#include <iostream> // cout, cin, cerr etc... +#include <fstream> // ifstream, ofstream +#include <string> + +int main() +{ + std::string sFilename = "MyFile.txt"; + + /****************************************** + * * + * WRITING * + * * + ******************************************/ + + std::ofstream fileSink(sFilename); // Creates an output file stream + + if (!fileSink) { + std::cerr << "Canot open " << sFilename << std::endl; + exit(-1); + } + + /* std::endl will automatically append the correct EOL */ + fileSink << "Hello Open Source World!" << std::endl; + + /****************************************** + * * + * READING * + * * + ******************************************/ + + std::ifstream fileSource(sFilename); // Creates an input file stream + + if (!fileSource) { + std::cerr << "Canot open " << sFilename << std::endl; + exit(-1); + } + else { + // Intermediate buffer + std::string buffer; + + // By default, the >> operator reads word by workd (till whitespace) + while (fileSource >> buffer) + { + std::cout << buffer << std::endl; + } + } + + exit(0); +} +``` + +该代码可以在 [GitHub][7] 上查看。当你编译并且执行它时，你应该能获得以下输出： + +![Console screenshot][8] + +(Stephan Avenwedde, [CC BY-SA 4.0][9]) + +这是个简易、适合初学者的例子。如果你想去使用该代码在你自己的应用中，最好遵从以下建议： + + * 文件流在程序结束的时候自动关闭。如果你想继续执行，那么应该通过调用 `close()` 方法手动关闭。 + * 这些文件流类继承自 [basic_ios][10]（在多个级别上），并且重载了 `!` 运算符。这使你可以进行简单的检查，是否可以访问该流。在 [cppreference.com][11] 上，你可以找到该检查何时会（或不会）成功的概述，并且可以进一步实现错误处理。 + * 默认情况下，`ifstream` 停在空白处并跳过它。要逐行读取直到到达 [EOF][13] ，请使用 `getline(...)` 方法。 + * 为了读写二进制文件，请将 `std::ios::binary` 标志传递给构造函数：这样可以防止 [EOL][13] 字符附加到每一行。 + +### 从系统角度进行写入 + +写入文件时，数据将写入系统的内存写入缓冲区中。当系统收到系统调用 [sync][14] 时，此缓冲区的内容将被写入硬盘。这也是你在不告知系统的情况下，不要卸下 U 盘的原因。通常，守护进程会定期调用 _sync_。为了安全起见，也可以手动调用 _sync_： + + +``` +#include <unistd.h> // needs to be included + +sync(); +``` + +### 总结 + +在 C++ 中读写文件并不那么复杂。更何况，如果你知道如何处理输入输出流，（原则上）那么你也知道如何处理任何类型的输入输出设备。对于各种输入输出设备的库能让你更容易地使用流运算符。这就是为什么知道输入输出流的流程会对你有所助益的原因。 + +-------------------------------------------------------------------------------- + +via: https://opensource.com/article/21/3/ccc-input-output + +作者：[Stephan Avenwedde][a] +选题：[lujun9972][b] +译者：[wyxplus](https://github.com/wyxplus) +校对：[校对者ID](https://github.com/校对者ID) + +本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 + +[a]: https://opensource.com/users/hansic99 +[b]: https://github.com/lujun9972 +[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/browser_screen_windows_files.png?itok=kLTeQUbY "Computer screen with files or windows open" +[2]: https://en.cppreference.com/w/cpp/io/ios_base +[3]: https://en.cppreference.com/w/cpp/io/basic_ofstream +[4]: https://en.cppreference.com/w/cpp/io/basic_ifstream +[5]: https://en.wikipedia.org/wiki/Separation_of_concerns +[6]: https://en.wikipedia.org/wiki/Dependency_injection +[7]: https://github.com/hANSIc99/cpp_input_output +[8]: https://opensource.com/sites/default/files/uploads/c_console_screenshot.png "Console screenshot" +[9]: https://creativecommons.org/licenses/by-sa/4.0/ +[10]: https://en.cppreference.com/w/cpp/io/basic_ios +[11]: https://en.cppreference.com/w/cpp/io/basic_ios/operator! +[12]: https://en.wikipedia.org/wiki/End-of-file +[13]: https://en.wikipedia.org/wiki/Newline +[14]: https://en.wikipedia.org/wiki/Sync_%28Unix%29 From 747f87b340527608592fbdf11fc1380acdf47573 Mon Sep 17 00:00:00 2001 From: wyxplus <32919297+wyxplus@users.noreply.github.com> Date: Wed, 31 Mar 2021 11:09:13 +0800 Subject: [PATCH 2/3] =?UTF-8?q?=E6=8F=90=E4=BA=A4=E7=BF=BB=E8=AF=91?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- translated/tech/20210326 How to read and write files in C.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/translated/tech/20210326 How to read and write files in C.md b/translated/tech/20210326 How to read and write files in C.md index 67d7b6c583..72250fde0f 100644 --- a/translated/tech/20210326 How to read and write files in C.md +++ b/translated/tech/20210326 How to read and write files in C.md @@ -10,7 +10,7 @@ 如何用 C++ 读写文件 ====== -如果你知道如何在 C++ 中使用输入输出I/O输入输出I/O流，那么你便能够（原则上）处理任何类型的输入输出设备。 +如果你知道如何在 C++ 中使用输入输出I/O流，那么你便能够（原则上）处理任何类型的输入输出设备。 ![Computer screen with files or windows open][1] From e9935bce9c50c0a721754261c456704ca1a1d8d4 Mon Sep 17 00:00:00 2001 From: wyxplus <32919297+wyxplus@users.noreply.github.com> Date: Wed, 31 Mar 2021 11:12:06 +0800 Subject: [PATCH 3/3] Update 20210326 How to read and write files in C.md --- translated/tech/20210326 How to read and write files in C.md | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/translated/tech/20210326 How to read and write files in C.md b/translated/tech/20210326 How to read and write files in C.md index 72250fde0f..63b71f7a6a 100644 --- a/translated/tech/20210326 How to read and write files in C.md +++ b/translated/tech/20210326 How to read and write files in C.md @@ -25,9 +25,9 @@ C++ 标准库提供了 [ios_base][2] 类。该类充当所有 I/O 流的基类 该两种类型都是在头文件 `` 中所定义。 -从 `ios_base` 继承的类在写入时可被视为数据接收器，在从其读取时可被视为数据源，与数据本身完全分离。这种面向对象的方法使 [关注点分离][5]separation of concerns[关注点分离][5]separation of concerns 和 [依赖注入][6]dependency injection[依赖注入][6]dependency injection 等概念易于实现。 +从 `ios_base` 继承的类在写入时可被视为数据接收器，在从其读取时可被视为数据源，与数据本身完全分离。这种面向对象的方法使 [关注点分离][5]separation of concerns 和 [依赖注入][6]dependency injection 等概念易于实现。 -### A simple example 一个简单的例子 +### 一个简单的例子 本例程是非常简单：实例化了一个 `ofstream` 来写入，和实例化一个 `ifstream` 来读取。