有没有大佬帮我看看这是怎么回事，关于sd库 DF创客社区

operator 发表于 2024-3-31 12:18:55

有没有大佬帮我看看这是怎么回事，关于sd库

<h3>以下是完整代码：</h3> #include<SD.h>#include<SPI.h>#include<String.h>unsigned long fileLength=0;//文件长度unsigned long poipos=0;//文件指针位置File file;String matchPinyin(String);String search(String,unsigned long,unsigned long);void setup() {  // put your setup code here, to run once:  Serial.begin(115200);  Serial.println(SD.begin(SPI_HALF_SPEED, 4));  File file=SD.open("1.txt",FILE_READ);  fileLength=file.available();  file.close();  Serial.println("汉字");  Serial.println(matchPinyin("a "));  Serial.println(matchPinyin("zuo "));  Serial.println(matchPinyin("hao "));  Serial.println("done");}String matchPinyin(String val){  return search(val,0,fileLength);}String search(String val,unsigned long a,unsigned long b)//传递原值，首位，末位，识别位数{  char word=0;//缓存所取  int sub=0;//比较下标  File file=SD.open("1.txt",FILE_READ);  unsigned long mid=a/2+b/2;  Serial.print(a);  Serial.print(",");  Serial.print(b);  Serial.print(":");  Serial.println(mid);  if((b-a)<2)  {    return "";  }  //Serial.println("front find");  file.seek(mid);  while(file.peek()!=10/*不是换行*/)//连续向上查询  {    /*Serial.print("    ");    Serial.print(mid);    Serial.print(" ");    Serial.println(file.peek());*/    mid--;    file.seek(mid);  }  //Serial.println("back find");  poipos=mid;  while(file.peek()!=9/*不是空格*/)//连续向下查询  {    /*Serial.print("    ");    Serial.print(file.peek());    Serial.print(" ");    Serial.println(char(file.peek()));*/    file.seek(++poipos);  }  while(file.seek(++poipos),(word=file.peek())!='\r'/*不是回车*/)//依次比较  {    /*Serial.print("   ");    Serial.print(char(val));    Serial.print("==");    Serial.print(char(word));*/    if(val==word)    {      sub++;    }    else if(word>val)//从前寻找    {      Serial.println("front");      yield();      file.close();      return(search(val,a,(a+b)/2));    }    else if(word<val)//从后寻找    {      Serial.println("back");      yield();      file.close();      return(search(val,(a+b)/2,b));    }  }  //此次选择正确  String ret="";  file.seek(++mid);  while(file.peek()!=9)  {    ret+=char(file.read());  }  file.close();  return ret;}void loop() {  // put your main code here, to run repeatedly:  } <h3>想做一个从SD卡里的文件用拼音查询汉字的程序，但是File file=SD.open("1.txt",FILE_READ); 这一句只能写到递归函数里，写到初始化里在递归函数里就不能操作文件了，是什么情况？怎么改进呢？</h3>        <figure class="image"><img></figure>    <h3> </h3><h3>以下是打开的文件（部分）</h3>   <figure class="image"><img></figure>

operator 发表于 2024-3-31 12:42:59

补两张图片

DFEDU 发表于 2024-4-1 17:56:08

试试这样
#include <SD.h>
#include <SPI.h>
#include <String.h>

unsigned long fileLength = 0; //文件长度
unsigned long poipos = 0; //文件指针位置
File file;

String matchPinyin(String);
String search(String, unsigned long, unsigned long, File &);

void setup()
{
Serial.begin(115200);
Serial.println(SD.begin(SPI_HALF_SPEED, 4));

file = SD.open("1.txt", FILE_READ);
fileLength = file.available();
file.close();

Serial.println("汉字");
Serial.println(matchPinyin("a "));
Serial.println(matchPinyin("zuo "));
Serial.println(matchPinyin("hao "));
Serial.println("done");
}

String matchPinyin(String val)
{
file = SD.open("1.txt", FILE_READ);
return search(val, 0, fileLength, file);
}

String search(String val, unsigned long a, unsigned long b, File &file)
{
char word = 0; //缓存所取
int sub = 0; //比较下标
unsigned long mid = a / 2 + b / 2;

Serial.print(a);
Serial.print(",");
Serial.print(b);
Serial.print(":");
Serial.println(mid);

if ((b - a) < 2)
{
return "";
}

file.seek(mid);
while (file.peek() != 10)
{
mid--;
file.seek(mid);
}

poipos = mid;
while (file.peek() != 9)
{
file.seek(++poipos);
}

while ((file.seek(++poipos), (word = file.peek())) != '\r')
{
if (val == word)
{
 sub++;
}
else if (word > val)
{
 Serial.println("front");
 yield();
 file.close();
 return (search(val, a, (a + b) / 2, file));
}
else if (word < val)
{
 Serial.println("back");
 yield();
 file.close();
 return (search(val, (a + b) / 2, b, file));
}
}

String ret = "";
file.seek(++mid);
while (file.peek() != 9)
{
ret += char(file.read());
}
return ret;
}

void loop()
{
}

operator 发表于 2024-4-2 22:56:06

DFEDU 发表于 2024-4-1 17:56
试试这样
#include
#include

问题解决了，谢谢！但是file是全局变量，为什么在初始化里赋值不可以？

开在边缘 发表于 2024-4-8 12:33:07

operator 发表于 2024-4-2 22:56
问题解决了，谢谢！但是file是全局变量，为什么在初始化里赋值不可以？

void setup() {
// put your setup code here, to run once:
Serial.begin(115200);
Serial.println(SD.begin(SPI_HALF_SPEED, 4));
File file=SD.open("1.txt",FILE_READ);

String search(String val,unsigned long a,unsigned long b)//传递原值，首位，末位，识别位数
{
char word=0;//缓存所取
int sub=0;//比较下标
File file=SD.open("1.txt",FILE_READ);

因为你在函数里面又重新定义了一次file，所以函数里面的file就变成了函数内部的局部变量，不再是你之前定义的那个全局变量了。

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有没有大佬帮我看看这是怎么回事，关于sd库