我尝试使用Auduino Uno通过线路ID读取/写入SD卡中的txt文件存储。但我没有成功。 请帮我。感谢
答案 0 :(得分：4)
您可以使用
if (myFile) {
while (myFile.available()) {
String line = myFile.readStringUntil('\n');
}
}
答案 1 :(得分：0)
请从 Arduino＆gt;开始例子＆gt; SD＆gt;读写：
/*
SD card read/write
This example shows how to read and write data to and from an SD card file
The circuit:
* SD card attached to SPI bus as follows:
** MOSI - pin 11
** MISO - pin 12
** CLK - pin 13
** CS - pin 4
created Nov 2010
by David A. Mellis
modified 9 Apr 2012
by Tom Igoe
This example code is in the public domain.
*/
#include <SPI.h>
#include <SD.h>
File myFile;
void setup()
{
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only
}
Serial.print("Initializing SD card...");
// On the Ethernet Shield, CS is pin 4. It's set as an output by default.
// Note that even if it's not used as the CS pin, the hardware SS pin
// (10 on most Arduino boards, 53 on the Mega) must be left as an output
// or the SD library functions will not work.
pinMode(10, OUTPUT);
if (!SD.begin(4)) {
Serial.println("initialization failed!");
return;
}
Serial.println("initialization done.");
// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
myFile = SD.open("test.txt", FILE_WRITE);
// if the file opened okay, write to it:
if (myFile) {
Serial.print("Writing to test.txt...");
myFile.println("testing 1, 2, 3.");
// close the file:
myFile.close();
Serial.println("done.");
} else {
// if the file didn't open, print an error:
Serial.println("error opening test.txt");
}
// re-open the file for reading:
myFile = SD.open("test.txt");
if (myFile) {
Serial.println("test.txt:");
// read from the file until there's nothing else in it:
while (myFile.available()) {
Serial.write(myFile.read());
}
// close the file:
myFile.close();
} else {
// if the file didn't open, print an error:
Serial.println("error opening test.txt");
}
}
void loop()
{
// nothing happens after setup
}
代码应该有效。确保您的引脚连接正确。
答案 2 :(得分：0)
不确定你是否仍需要这方面的帮助，但现在就去了。
请尝试在ID之间插入“\ r \ n”，而不是使用br标记。例如，如果要通过创建PHP + SQL数据库查询并将结果写入文件来创建login.txt，请将代码中的br替换为“\ r \ n”。或者，如果您能够打开并编辑login.txt，请执行此操作，并使用新行替换每个br。
然后您需要做的就是逐个读取文件中的每一行。
#include <SD.h>
#include <SPI.h>
int CS_PIN = 10;
char logfile[] = {"login.txt"};
File file;
void setup() {
Serial.begin(9600);
initializeSD();
openFile(logfile);
while(file.available()) {
// print the lines to serial monitor
Serial.println(readLine());
}
closeFile();
}
void loop() {
}
void initializeSD() {
Serial.println("Initializing SD card...");
pinMode(CS_PIN, OUTPUT);
if (SD.begin()) {
Serial.println("SD card is ready to use.");
} else {
Serial.println("SD card initialization failed");
return;
}
}
void closeFile() {
if (file) {
file.close();
Serial.println("File closed");
}
}
int openFile(char filename[]) {
file = SD.open(filename);
if (file) {
Serial.println("File opened with success!");
return 1;
} else {
Serial.println("Error opening file...");
return 0;
}
}
String readLine() {
String received = "";
char ch;
while (file.available()) {
ch = file.read();
if (ch == '\n') {
return String(received);
} else {
received += ch;
}
}
return "";
}
这是一个缩短的，未经测试的，并在此YouTube link上发布的代码稍加修改（请参阅视频说明以获取完整代码的链接）。另外，请务必仔细检查接线，如图所示。
如果您无法更改login.txt文件的结构，并且只能从SD卡读取它，请尝试使用此代码以便从文件中读取（第一个建议中的文件的修改版本）：
String readLine() {
String received = "";
char ch;
while (file.available()) {
ch = file.read();
if (ch == '<') { // Is the tag starting?
return String(received); // Return what you have so far (ID)
} else if(ch == '>') { // Is the tag ending?
received = ""; // Empty the string, we don't need br
} else { // Everything's OK, append to the string
received += ch;
}
}
return "";
}
请注意，两个建议都不会将这些行存储到单独的变量中。我建议您使用文件中的每一行执行您想要执行的操作（打印到串行，闪烁LED等），阅读时。
答案 3 :(得分：0)
塔文森的答案是正确的
if (myFile) {
while (myFile.available()) {
String line = myFile.readStringUntil('\n');
}
}