將Arduino F（）宏與字符串數組一起使用

Question

我正在開發一個Arduino項目，可以在LCD屏幕上打印隨機引用。 大約有一百種不同的引號，但其中包含超過10種引號會使SRAM過載。

我已經調查了它，似乎我需要使用PROGMEM或F()將字符串存儲在閃存而不是SRAM中，但我無法弄清楚要存儲的語法，然后檢索它們。 當前程序看起來像這樣（偽代碼刪除不相關的部分）：

String quotes[] = {"quote 1", "quote2", "quote3", ... "quoteN"};
String currentQuote;    

void setup() {
  currentQuote = quotes[0];
}

void loop() {
  if (condition)
      currentQuote = quotes[random(N)];
}

如何將我的字符串數組存儲在閃存中，然后在需要時檢索單個元素？

Answer 1

直接來自http://arduino.cc/en/Reference/PROGMEM

It is important to use the datatypes outlined in pgmspace.h. 
Some cryptic bugs are generated by using ordinary datatypes for program memory calls.
Below is a list of variable types to use. 
Floating point numbers in program memory do not appear to be supported.

prog_char      - a signed char (1 byte) -127 to 128
prog_uchar     - an unsigned char (1 byte) 0 to 255
prog_int16_t   - a signed int (2 bytes) -32,767 to 32,768
prog_uint16_t  - an unsigned int (2 bytes) 0 to 65,535
prog_int32_t   - a signed long (4 bytes) -2,147,483,648 to * 2,147,483,647.
prog_uint32_t  - an unsigned long (4 bytes) 0 to 4,294,967,295

所以你不能使用String類型。 我建議使用引號[]的另一個定義，例如：

char a[][]={
    "quote1",
    "quote2",
    "...",
    "quoten",

};

順便說一句，同一頁http://arduino.cc/en/Reference/PROGMEM有一個你需要的例子：

/*
 PROGMEM string demo
 How to store a table of strings in program memory (flash), 
 and retrieve them.

 Information summarized from:
 http://www.nongnu.org/avr-libc/user-manual/pgmspace.html

 Setting up a table (array) of strings in program memory is slightly complicated, but
 here is a good template to follow. 

 Setting up the strings is a two-step process. First define the strings.

*/

#include <avr/pgmspace.h>
prog_char string_0[] PROGMEM = "String 0";   // "String 0" etc are strings to store - change to suit.
prog_char string_1[] PROGMEM = "String 1";
prog_char string_2[] PROGMEM = "String 2";
prog_char string_3[] PROGMEM = "String 3";
prog_char string_4[] PROGMEM = "String 4";
prog_char string_5[] PROGMEM = "String 5";


// Then set up a table to refer to your strings.

PROGMEM const char *string_table[] =       // change "string_table" name to suit
{   
  string_0,
  string_1,
  string_2,
  string_3,
  string_4,
  string_5 };

char buffer[30];    // make sure this is large enough for the largest string it must hold

void setup()              
{
  Serial.begin(9600);
}


void loop()           
{
  /* Using the string table in program memory requires the use of special functions to retrieve the data.
     The strcpy_P function copies a string from program space to a string in RAM ("buffer"). 
     Make sure your receiving string in RAM  is large enough to hold whatever
     you are retrieving from program space. */


  for (int i = 0; i < 6; i++)
  {
strcpy_P(buffer, (char*)pgm_read_word(&(string_table[i]))); // Necessary casts and dereferencing, just copy.     
    Serial.println( buffer );
    delay( 500 );
  }
}

Answer 2

我在代碼中看到String類中支持F（）。 但我不知道如何使用它。

我建議查看http://arduino.cc/en/Reference/PROGMEM，它解釋了PROGMEM的使用相當好，並且與您的應用程序相關。 我認為PROGMEM更適用於char字符串，而不是字符串。