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Index › Programming Questions & Help › Syntax Questions › file I/O

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file I/O (Read 1009 times)

PeterT YaBB Newbies Offline Posts: 5	file I/O Jul 7^th, 2009, 10:55am Hi, I want to learn how to open a file - write to it - close it - and perhaps open it later and add something to it. Like something you would like to do when logging data from something you read off an Arduino board. Can anyone show me a simple example of this? I am a beginner, oh verily....

blindfish God Member Offline Posts: 793	Re: file I/O Reply #1 - Jul 7^th, 2009, 12:02pm Sounds like you need loadStrings() and saveStrings()...
	Where is the what if the what is in why?

PeterT

Re: file I/O
Reply #2 - Jul 11^th, 2009, 4:00am

ahhh - I see; to achieve the 'append' feature I am looking for, first read in what is in the file already, then add to this, then write out?

I tried this, but I am obviously missing on several cylinders - here is code that I thought would work. The error message I get is "Syntax error, maybe a missing right parenthesis?" and the line

fileAppend(String filename,String words);

is highlighted. I don't think that is the problem - maybe I am miles out and the error message is just one of several possibilities. I guess I need more help, or a pointer to a place where this stuff is covered.

Cheers, Peter.

// Test of adding text to a file if it exists

void setup() {
//
}

void draw() {
//

string filename= "nouns.txt";
string words = "apple bear cat dog";
fileAppend(String filename,String words);
}

void fileAppend() {
// first try to read from file
//
String filestuff = loadStrings(filename);
// then, depending on what was found, do either ...
if (filestuff == null) {
// file is empty, just write words out, one per line
String[] list = split(words, ' ');
saveStrings(filename, list);
}
// or ...
else {
// file has stuff in it, append words to filestuff, and write all of it out

// ... more code later
println("Pretend writing ...");

}
}

« Last Edit: Jul 11^th, 2009, 7:24am by PeterT »

alvaro

Re: file I/O
Reply #3 - Jul 11^th, 2009, 7:23am

Code:


/*
draw() gets called automatically several times a second. So depending on what you want to do, you should put your call to fileAppend() in a more relaxed place, like setup (but then, that depends on what you want to do)
*/
void setup() {

/*
When you declare a variable to be of type String, the word String should be capitalized. String is a class in Java / Processing, class names are always capitalized.
*/
  String filename= "nouns.txt";
  String words = "apple bear cat dog";

/*
This is a method call. Just put the names of the variables in here, without their types.
*/
  fileAppend(filename, words); 
}

/*
This is the method definition, put the types of the parameters here
*/
void fileAppend(String filename,String words) {

  /* loadstrings returns an array of Strings */
  String[] filestuff = loadStrings(filename);

  // then, depending on what was found, do either ...
  ....
}

PeterT YaBB Newbies Offline Posts: 5	Re: file I/O Reply #4 - Jul 11^th, 2009, 7:34am Thanks! I am new to Processing, and it seems a long way to go to write to a file I must be trying to do something that is out there as example code already? Thanks for the help - I will post the code once it is finished and works. Cheers, Peter

PeterT

Re: file I/O
Reply #5 - Jul 11^th, 2009, 10:34am

All right, here is my first attempt at setting up a Processing sketch that will allow the addition of words at the end of a preexisting file:

// Test of adding text to an existing file

void setup() {
//

String filename= "nouns.txt"; // Name of the file - which must exist in sketch folder
String words = "straw tree bush"; // List of words to add to the file
fileAppend( filename, words); // The call
}

void fileAppend(String filename,String words) {

/*

Processing routine to split 'words' into a list, and add
them on seperate lines at the end of the file 'filename'.

*/

// Split input words into a list
String[] list = split(words, ' ');
// read from (necessarily existing) file
String[] filestuff = loadStrings(filename);
//
String[] newlist = new String[list.length+filestuff.length];
// add old stuff to new list
for(int i=0; i < filestuff.length; i++) {
newlist[i] = filestuff[i];
}
// Add new stuff to new list
for(int i=0; i < list.length; i++) {
newlist[i+filestuff.length] = list[i];
}
// then write complete array to file
saveStrings(filename, newlist);
}

I still need to work out how to do the above but with numbers (integers and floats) and what to do when the file does not already exist. Thanks for the help I received!

Peter

alvaro Junior Member Offline Posts: 85 Berlin	Re: file I/O Reply #6 - Jul 11^th, 2009, 11:15am it compiles! let's ship it! no seriously pretty cool for a first attempt.

PeterT YaBB Newbies Offline Posts: 5	Re: file I/O Reply #7 - Jul 11^th, 2009, 1:20pm Thanks At one point I had : String newlist[] = instead of: String[] newlist = and it worked fine - is that a bug or a feature of Processing?

alvaro Junior Member Offline Posts: 85 Berlin	Re: file I/O Reply #8 - Jul 11^th, 2009, 3:13pm both notations mean exactly the same thing. It probably has some deep historical reasons or maybe somebody made a typo. Anyway the general declaration of an array goes: Type[] name = new Type[number]; or Type name[] = new Type[number];

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