我想知道 volatile 关键字与注册, const 和静态的不同用法,关键字。我不知道是什么影响,所以我想:
注册volatile int T = 10;建议编译器将T存储在寄存器中,T的值可以从外部OS,硬件,另一个线程)
const volatile int T = 10;程序本身不能修改T,但是T可以在代码之外的地方修改。 p>
static volatile int T = 10;如果T是类的数据成员,则表示类的所有对象都具有相同T和T的值可以从外部修改。如果T是文件中的全局变量,则其他文件(作为项目的一部分)中的源代码无法访问T,但是T可以从外部访问。如果T是一个函数中的局部变量,一旦它被初始化,就会保留在内存中,直到程序结束,并且可以从外部修改。
思想是正确的,任何经验丰富的C ++开发人员都可以给出一个例子,上面的例子可能在现实世界的应用程序中使用,或者是非常罕见的。
解决方案pre> register volatile int T = 10;
volatile 限定符意味着编译器不能应用优化或重新访问 T ,而寄存器是提示编译器 T 将被大量使用。如果采用 T 的地址,编译器将忽略提示。请注意,寄存器已弃用,但仍在使用。
实用用法:
我从来没有使用过它,从来没有感觉到它的需要,
const volatile int T = 10;const 限定符表示 T 无法通过代码修改。如果尝试这样做,编译器将提供诊断。 volatile 仍然意味着与情况1相同。编译器无法优化或重新排序对 T 的访问。
实用用法:
- 以只读模式存取共享内存。
- 以只读模式访问硬件寄存器。
static c> T 静态存储持续时间(C ++ 11§3.7)和内部链接,而 volatile 仍然管理优化和重新排序。
实用用法:
- 与 volatile 相同,除了您需要对象具有静态存储时长,并且无法从其他翻译单位访问。
I am wondering about the different uses of the volatile keyword in combination with register, const and static keywords. I am not sure what are the effects, so I think:
register volatile int T=10;Suggest the compiler to store T in a register and the value of T can be modified from somewhere outside (OS, hardware, another thread)
const volatile int T=10;The program itself can not modify T, but T can be modified frow somewhere outside the code.
static volatile int T=10;If T is a data member of a class it means that all the objects of the class have the same value for T and T can be modified from somewhere outside. If T is a global variable in a file, the source code in other files (that are part of the project) cannot access T, but T can be accessed from somewhere outside. If T is a local variable in a function,once it has been initialized remains in the memory until the end of the program and can be modified from somewhere outside.
Are my thoughts correct and can any experienced C++ developer give an example where the above maybe used in real-world applications or it is very rare?
解决方案 register volatile int T=10;volatile qualifier means that the compiler cannot apply optimizations or reorder access to T, While register is a hint to the compiler that T will be heavily used. If address of T is taken, the hint is simply ignored by the compiler. Note that register is deprecated but still used.
Practical Usage:
I have never used it never felt the need for it and can't really think of any right now.
const volatile int T=10;const qualifier means that the T cannot be modified through code. If you attempt to do so the compiler will provide a diagnostic. volatile still means the same as in case 1. The compiler cannot optimize or reorder access to T.
Practical Usage:
- Accessing shared memory in read-only mode.
- Accessing hardware registers in read-only mode.
static storage qualifier gives T static storage duration (C++11 §3.7) and internal linkage, while volatile still governs the optimization and reordering.
Practical Usage:
- Same as volatile except that you need the object to have static storage duration and to be inaccessible from other translation units.
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const volatile,寄存器volatile,C ++中的静态volatile
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