如何解决指针和PROGMEM的问题
我在Arduino UNO上编程,遇到了非常烦人的路障。
我在PROGMEM中遇到了一个非常奇怪的问题,我将其范围缩小到了指针数组的问题。
当我用变量j索引PROGMEM数组时。根据天气的不同,它会返回不同的结果,变量j是由静态数字设置还是由另一个变量设置。
程序号是存储在对象中的整数,并且只能按以下方式设置,对内存进行分配并且变量保留其值。我已经测试过了。
*(this->program) = 0;
将j设置为0直接产生正确的地址
uint16_t j = 0;
Serial.println(j);
//printed 0 as expected
address = (uint16_t)*(pgmStringTable + (uint16_t)j);
Serial.println(address);
//gave address = 105,which is correct and PROGMEM reads the correct bytes
但是,如下使用progam变量设置j会产生错误的地址
uint16_t j = *(this->program);
Serial.println(j);
//printed 0 as expected
address = (uint16_t)*(pgmStringTable + (uint16_t)j);
Serial.println(address);
//gave address = 4,which isnt right and results in PROGMEM read errors
即使尝试解决此设置问题,例如对*(this-> program)进行算术运算或将其发送到返回相同值的整数的函数也无济于事。唯一有效的方法是遍历所有整数,如下所示:
//loops through most unsigned integer values
for(uint16_t j = 0; j < 65000; j++){
if(j == *(this->program)){
address = (uint16_t)*(pgmStringTable + (uint16_t)j);
//address is correct and PROGMEM works correctly
}
}
上述工作甚至是确认malloc正常工作的更多原因,因为*(this-> program)在与j比较时返回正确的值。
这是一个非常糟糕的解决方法,因为它效率很低,并且会导致我的程序浪费大量的时间,这对时间很敏感。
任何指向解决方案的指针或该指针表现为滑稽的原因都将非常有用。
问题出在一个非常大的项目中,因此为了缩小错误范围,我在一个更小的.ino文件中重新创建了该问题
整个代码是这个。上传我的arduino UNO时,它产生了相同的错误
编辑:
- 在进一步研究中,将j设置为在我的主项目中不是恒定的任何变量(因此该变量不能在项目中的其他任何地方)似乎以与上述相同的方式破坏了PGM。
const char pgmString1[] PROGMEM = "String 1__";
const char pgmString2[] PROGMEM = "2nd String";
const char *const pgmStringTable[] PROGMEM = {pgmString1,pgmString2};
class testObject{
private:
uint16_t* program;
public:
testObject(){
program = (uint16_t*) malloc(sizeof(uint16_t));
*(this->program) = 0;
}
void read(){
if(*(this->program) == 0){
//the console prints the below,meaning the value is definitly 0
Serial.println("it was 0");
*(this->program) = 0;
}else{
Serial.println("it wasnt 0");
//if this is uncommeneted,this program outputs the correct values but the above comment will not be dispalyed
//*(this->program) = 0;
}
char temp[10];
uint16_t j = 0;
uint16_t address = 0;
////////////////////////////////////////////// indirectly setting j
//sets the j value to be 0,which is what is stored in this->program
j = *(this->program);
//prints j to make sure its 0,then finds the address of the progmem string
Serial.print(j);
Serial.print(" 1 Address: |");
address = (uint16_t)*(pgmStringTable + (uint16_t)j);
Serial.print(address); //the address printed is incorrect
Serial.print(" ");
//reads byte by byte from the address,it reads the wrong bytes
for(int i = 0; i < 10; i++){
char myChar = pgm_read_byte( address + i );
Serial.print(myChar);
}
Serial.println("\n");
////////////////////////////////////////////// directly setting j
//but just setting j = 0 works fine
j=0;
//so directly setting j as 0,same code as above but it produces the correct output
//SAME AS ABOVE,COULDNT SEPERATE INTO ITS ONW FUNCTION
Serial.print(j);
Serial.print(" 2 Address: |");
address = (uint16_t)*(pgmStringTable + (uint16_t)j);
Serial.print(address);
Serial.print(" ");
for(int i = 0; i < 10; i++){
char myChar = pgm_read_byte( address + i );
Serial.print(myChar);
}
Serial.println();
//
}
};
testObject pgmReader;
void setup(){
Serial.begin(9600);
}
void loop(){
Serial.println("\n\n\n\n\n\n\n\n");
delay(1000);
pgmReader.read();
}
解决方法
不仅pgmString1
和pgmString2
也是pgmStringTable
都是PROGMEM。因此,您必须使用pgm_read_
函数来读取pgmStringTable
。
address = pgm_read_ptr(pgmStringTable + (uint16_t)j);
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