关于Arduino上的strcpy和内存

问题描述

我正在我的 Arduino Uno 上运行这段代码:

I'm running this code on my Arduino Uno:

#include <stdlib.h>


#include <Arduino.h>
#include <SoftwareSerial.h>
#include <MemoryFree.h>


void setup() {
  Serial.begin(9600);
  char cc[300];
  char* ce = "Bonjour ca va et toi ?Bonjour ca va et toi ?Bonjour ca va et toi ?Bonjour ca va et toi ?";
  strcpy(cc, ce, 300);
  Serial.println(getFreeMemory());
}

void loop() {
  // Put your main code here, to run repeatedly:

}

所以我想看看这占用了多少内存.我很惊讶，它不是我预期的300，而是300 + len(cc).我想我不明白 strcpy 的工作原理.但是我认为这段代码会将ce复制到cc并且不会使用更多的内存.

So I wanted to see how much memory this was taking. And I was surprised that it was not 300 as I expected, but 300 + len(cc). I think I don't understand how strcpy works. But I thought this code would copy ce into cc and wouldn't use more memory.

另一件事:当我在没有strcpy的情况下运行代码时，好像SRAM中什么都没有.

Another thing: When I run the code without the strcpy it's like nothing was in my SRAM.

推荐答案

您缺少的部分是双引号字符串常量同时使用了闪存(程序大小)和RAM.不是因为strcpy而是因为这是此哈佛架构MCU上不同类型的内存的产物.

The part you're missing is that double-quoted string constants use both flash memory (program size) and RAM. It's not because of strcpy; it's an artifact of the different types of memory on this Harvard Architecture MCU.

为避免将Flash和RAM都用作字符串常量，请使用F宏强制仅从Flash对其进行访问:

To avoid using both flash and RAM for string constants, use the F macro to force it to be accessible from flash ONLY:

void setup() {
  Serial.begin(9600);
  char cc[300];
  strcpy_P(cc, (const char *) F("Bonjour ca va et toi ?Bonjour ca va et toi ?"
                                "Bonjour ca va et toi ?Bonjour ca va et toi ?") );
  Serial.println(getFreeMemory());
}

...或将其定义为PROGMEM字符数组:

... or define it as a PROGMEM character array:

const char ce[] PROGMEM =
        "Bonjour ca va et toi ?Bonjour ca va et toi ?"
        "Bonjour ca va et toi ?Bonjour ca va et toi ?";

void setup() {
  Serial.begin(9600);
  char cc[300];
  strcpy_P(cc,ce);
  Serial.println(getFreeMemory());
}

注意:

• 您必须使用strcpy_P变体从闪存而不是RAM复制.
长双引号字符串可以分解为几个相邻的双引号字符串.编译器将为您串联它们.

NOTES:

• you have to use the strcpy_P variant to copy from flash, not RAM.
• long double-quoted strings can be broken up into several adjacent double-quoted strings. The compiler will concatenate them for you.

如果您可以用这些东西做事"，那么您可能不需要一个大数组.例如，请勿制作一个大阵列，以便您可以打印或发送它.只需打印或发送各个片段-一些片段来自RAM(例如变量)，而另一些片段来自flash(例如双引号字符串常量).这样可以节省RAM(很多！)和处理时间(没有副本或串联).

You may not need one big array if you can do your "thing" with the pieces. For example, don't make one big array so you can print or send it. Just print or send the individual pieces -- some pieces from RAM (e.g., variables) and some from flash (e.g., double-quoted string constants). This saves RAM (lots!) and processing time (no copies or concatenations).

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