在C / C ++中直接写入内存地址的最短代码是什么？ [英] What's the shortest code to write directly to a memory address in C/C++?

问题描述

我为没有内存保护的嵌入式系统编写系统级代码（在ARM Cortex-M1上，用gcc 4.3编译），需要直接读/写内存映射寄存器。到目前为止，我的代码看起来像这样：

I'm writing system-level code for an embedded system without memory protection (on an ARM Cortex-M1, compiling with gcc 4.3) and need to read/write directly to a memory-mapped register. So far, my code looks like this:

#define UART0     0x4000C000
#define UART0CTL  (UART0 + 0x30)

volatile unsigned int *p;
p = UART0CTL;
*p &= ~1;

有没有更短的方式（代码更短，我的意思），不使用指针？我正在寻找一种方法来写这么短的实际分配代码（如果我不得不使用更多的#defines就没问题）：

Is there any shorter way (shorter in code, I mean) that does not use a pointer? I looking for a way to write the actual assignment code as short as this (it would be okay if I had to use more #defines):

*(UART0CTL) &= ~1;

到目前为止，我尝试的任何事情都是由gcc抱怨它无法分配给lvalue的东西。 。

Anything I tried so far ended up with gcc complaining that it could not assign something to the lvalue...

推荐答案

我想成为一个nitpick：我们在说C或C ++吗？

I'd like to be a nitpick: are we talking C or C++ ?

如果C，我推迟到Chris的回答（我想要删除C ++标记）。

If C, I defer to Chris' answer willingly (and I'd like the C++ tag to be removed).

如果C ++，建议不要使用那些讨厌的C-Casts和 #define 。

If C++, I advise against the use of those nasty C-Casts and #define altogether.

惯用的C ++方法是使用全局变量：

The idiomatic C++ way is to use a global variable:

volatile unsigned int& UART0 = *((volatile unsigned int*)0x4000C000);
volatile unsigned int& UART0CTL = *(&UART0 + 0x0C);

我声明一个键入的全局变量，它将遵守范围规则宏）。

I declare a typed global variable, which will obey scope rules (unlike macros).

它可以很容易地使用（不需要使用 *（））， ！

It can be used easily (no need to use *()) and is thus even shorter!

UART0CTL &= ~1; // no need to dereference, it's already a reference

如果你想它是指针，将是：

If you want it to be pointer, then it would be:

volatile unsigned int* const UART0 = 0x4000C000; // Note the const to prevent rebinding

但是使用 const 指针不能为null？这在语义上为什么引用被创建为

But what is the point of using a const pointer that cannot be null ? This is semantically why references were created for.

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