I only want to know latitude and longitude, so I'd like to read each line individually and then separate the string so that only << lat="......." lon="....." >> remain.
My problem is how to read only one line? I don't understand the MediaTek documentation because there are no examples. This is the docu. What does the void * buf part mean? What do I have to insert there?
If you know another way how to read a file line by line I would be happy to hear.
Sorry for my question does not adress an arduino problem directly but more of a programming in C toppic. I just hope there are enough programming pros who can help me
I'm using the LinkIt One. Not an Arduino directly but it uses the Arduino.exe programm for PC and its libraries so I thought I can find some help here.
btsens:
I'm using the LinkIt One. Not an Arduino directly but it uses the Arduino.exe programm for PC and its libraries so I thought I can find some help here.
Right, if it uses the Arduino IDE and libraries than it should be fine. (I had no idea what a LinkIt was.)
So I guess "LFile" is a library that you include, based on the Arduino "Stream" class. I was just wondering if we were speaking the same language.
OldSteve:
Right, if it uses the Arduino IDE and libraries than it should be fine. (I had no idea what a LinkIt was.)
So I guess "LFile" is a library that you include, based on the Arduino "Stream" class. I was just wondering if we were speaking the same language.
The LFile comes from a library for the LinkIt for storage access. The board has Flash storage and an SD slot, so they have a library a little different from the arduino ones (I guess? Though arduino has no SD slot on board as far as I know, so the libraries should be from the distributors of SD shields?)
The main problem is that in this library there is no such thing as .readline included as I know it from C# or JAVA programming. The whole thing with reading data is relatively new for me.
but all I get is a row full of "255" and the last number is "239"...I guess this is not how this works
Probably this is because the read() method is in int. But why should read() be int? Wouldn't it be much more sensible to get data as a char or string? I don't find other methods though, with which I could read a file.
Edit: Problem found (partly): If I use Serial.write instead of Serial.println I get the whole document (as long as I just use dataFile.read();). Though when I use dataFile.read(buff, 50); I get a line full of "2"...
btsens:
The LFile comes from a library for the LinkIt for storage access. The board has Flash storage and an SD slot, so they have a library a little different from the arduino ones (I guess? Though arduino has no SD slot on board as far as I know, so the libraries should be from the distributors of SD shields?)
The main problem is that in this library there is no such thing as .readline included as I know it from C# or JAVA programming. The whole thing with reading data is relatively new for me.
If you want to read each line into a buffer, then parse it, you might be better to use the single byte version of 'read()', and check each char that's read for a newline character, '\n', to signify the end of the line. Then you could use 'strstr()' to find lat=" or long=", followed by 'parseFloat()' (Edit: Silly mistake.) 'strtof()' to retrieve the value.
To use the single byte version of 'read()', you'd do this:-
char c = dataFile.read();
I'm far from an expert on this, so someone else will probably help with a better method.
I just saw your latest reply. You can't use the multi-byte version of 'read()' like that. The return value is the number of bytes read, so it should be 255. (The bytes received will be stored in the buffer that you passed the address of.)
OldSteve:
If you want to read each line into a buffer, then parse it, you might be better to use the single byte version of 'read()', and check each char that's read for a newline character, '\n', to signify the end of the line. Then you could use 'strstr()' to find lat=" or long=", followed by 'parseFloat()' to retrieve the value.
To use the single byte version of 'read()', you'd do this:-
char c = dataFile.read();
I'm far from an expert on this, so someone else will probably help with a better method.
I just saw your latest reply. You can't use the multi-byte version of 'read()' like that. The return value is the number of bytes read, so it should be 255. (The bytes received will be stored in the buffer that you passed the address of.)
All right, I will try with this version. I guess with some "if"s and "while"s I should make this work. Thank you
This will probably work; it will read one character at a time till it finds the newline character (it depends on how the file is generated if it is '\n\ or '\r'). Once the '\n' is found, it's replaced by the nul character (so it's valid c-style string) and displayed.
void loop()
{
static int index = 0;
if (dataFile)
{
if (index >= sizeof(buff))
{
Serial.println("buffer overflow prevented; data discarded");
index = 0;
}
if (dataFile.available())
{
// read a character and place in buffer
buff[index] = dataFile.read();
// if newline character
if (buff[index] == '\n')
{
// replace with nul terminator
buff[index] = '\0';
// reset index
index = 0;
// display
Serial.println(buff);
}
else
{
// for next read, character should be stored in next position
index++;
}
}
}
}
Note that it uses loop() to do the looping; for setup() you need to modify it a little
sterretje:
This will probably work; it will read one character at a time till it finds the newline character (it depends on how the file is generated if it is '\n\ or '\r'). Once the '\n' is found, it's replaced by the nul character (so it's valid c-style string) and displayed.
void loop()
{
static int index = 0;
if (dataFile)
{
if (index >= sizeof(buff))
{
Serial.println("buffer overflow prevented; data discarded");
index = 0;
}
if (dataFile.available())
{
// read a character and place in buffer
buff[index] = dataFile.read();
// if newline character
if (buff[index] == '\n')
{
// replace with nul terminator
buff[index] = '\0';
// reset index
index = 0;
// display
Serial.println(buff);
}
else
{
// for next read, character should be stored in next position
index++;
}
}
}
}
Note that it uses loop() to do the looping; for setup() you need to modify it a little ;)
Thanks for the help. I'm cooking a meal right now, and didn't have time to show how to retrieve each line.
As I said, I'm no expert, so there's probably a better method of parsing than using 'strstr()' followed by 'parseFloat()'(Edit: Silly mistake again.) 'strtof()', but it should work.
Back to the food.........
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
Drv.begin();
dataFile=Drv.open("Windach_bahnen.gpx", FILE_READ);
char readline;
String line="";
if(dataFile){
while(dataFile.available()){
readline=dataFile.read();
while(readline!='\n' && readline!='\r'){
line+=readline;
readline=dataFile.read();
}
Serial.println(line);
line="";
}
}
}
So now I just need to parse my string "line" at the points I want to :) Thank you very much for your help. I appreciate it a lot.
'I for got to add, 'strstr()' points to the first character of the search string, so you'll need to add the length of the search string to the returned pointer, to point at the first character of the float.
Oops, and 'parseFloat()' won't work on a string. I was rushing. You'll need to use 'strtof()'. Sorry. :-[
Edit: I just noticed you've changed to using the "String" class. The C string functions 'strstr()' and 'strtof()' won't work with that class. You're better to stick to C strings. Take a look at sterretje's suggestion. (No "String" class.)
