如何只执行一段代码？ [英] How to execute a piece of code only once?

问题描述

我有一个应用程序，它有几个功能。根据用户输入可以多次调用每个功能。但是，我只需要在应用程序启动时执行一次函数中的一小段代码。当在稍后的时间再次调用这个相同的函数时，这段代码不能被执行。代码位于 VC ++ 中。请告诉我处理这种情况的最有效的方法。

解决方案

在构造函数中使用全局静态对象$ C>主）？或者只是在一个例程中

  static bool initialized; 
 if（！initialized）{
 initialized = true; 
 //执行初始化部分
} 
  

这还不够快！

---

addenda

在多线程这可能是不够的：

您可能也对 pthread_once 或 功能 __属性__ GCC 。

使用C ++ 11，您可能需要 std :: call_once 。

您可能需要使用 < atomic> 并且可能会声明 static volatile std :: atomic_bool initialized; （但你编辑小心）如果你的函数可以从多个线程中调用。

^{但是这些可能不适用于你的系统。它们在Linux上可用！}

I have an application which has several functions in it. Each function can be called many times based on user input. However I need to execute a small segment of the code within a function only once, initially when the application is launched. When this same function is called again at a later point of time, this particular piece of code must not be executed. The code is in VC++. Please tell me the most efficient way of handling this.

解决方案

Use global static objects with constructors (which are called before main)? Or just inside a routine

static bool initialized;
if (!initialized) {
   initialized = true;
   // do the initialization part
}

There are very few cases when this is not fast enough!

---

addenda

In multithreaded context this might not be enough:

You may also be interested in pthread_once or constructor function __attribute__ of GCC.

With C++11, you may want std::call_once.

You may want to use <atomic> and perhaps declare static volatile std::atomic_bool initialized; (but you need to be careful) if your function can be called from several threads.

^{But these might not be available on your system; they are available on Linux!}

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