Incrementing file names

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nigelf
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Posted by nigelf: Sun. Feb 2, 2014 - 12:50 AM
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I searched but didn't find any sort of meaningful answer, can you help guys?

I am trying to load from an SD card, graphic data into the on board serial flash memory files for a 7" CTE LCD display.

all goes well 0 to 9 but then will not increment to 10.

the File names are 0.CTE 1.CTE ... and so on.

the 10th increment looks for a file called :.CTE (I think that's because that's the character next in the ASCII table)

if I call for 10.CTE the next increment is 20.CTE!

is this a well know gotcha? and is there a work around 

IMAGE_FILENAME[0]=IMAGE_FILENAME[0]++;

this is how it increments.

Regards
Nigel

Tags:

AVR Microcontrollers, megaAVR and tinyAVR
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cooluser
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Posted by cooluser: Sun. Feb 2, 2014 - 04:21 AM
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"9 + 1 is :" in the micro world.. In the code treat the numbers always as integers.. I would suggest having something like this

int file_name = 10;
//convert it to ascii and access the *.CTE file
access_cte_file(itoa(filename));

You can even write a manual routine for that..

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mikech
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Posted by mikech: Sun. Feb 2, 2014 - 04:43 AM
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More information is required, specifically, the code that constructs the filenames n.CTE using what is in array IMAGE_FILENAME[]

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Gold Markclawson
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Posted by clawson: Sun. Feb 2, 2014 - 12:56 PM
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I'd just sprintf() to create the filename. You can then do stuff like leading zero padding.

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Torby
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Posted by Torby: Sun. Feb 2, 2014 - 01:17 PM
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One day, I really need to learn to use sprintf.

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Gold Markclawson
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Posted by clawson: Sun. Feb 2, 2014 - 01:19 PM
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It's just printf() into a buffer ;-)

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nigelf
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Posted by nigelf: Sun. Feb 2, 2014 - 02:19 PM
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I may be talking cross purposes here but each file is created in GIMP a graphics program and as such named by me when I save the file. Each file is a jpg icon which is then converted to a different format and again named by me when saved as the .CTE file.

Its the SD to serial memory transfer that's not getting past the 9.CTE file!

attached file is the code (arduino)

Attachment(s): 

Plain text icon the code insertion didn't work for me so attached as a txt file
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Gold Markclawson
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Posted by clawson: Sun. Feb 2, 2014 - 02:54 PM
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Yeah but the reason is obvious isn't it? What do you think '9'+1 is? If you answered "10" you don't understand ASCII / C.

As I say sprintf is the obvious answer here. Some people will say sprintf/printf uses too much flash space. But you are already doing SD/FAT which already costs 20-30K so the odd extra 1-2K doesn't really matter does it?

Apart from anything else:

char IMAGE_FILENAME[] = "0.CTE";

where does "10.CTE" fit into the storage allocated for that string?

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nigelf
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Posted by nigelf: Sun. Feb 2, 2014 - 03:24 PM
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Yes you are correct I don't understand C or ASCCI, I mean how does the string "0.CTE" plus 1 equal "1.CTE"

why would it increment the 0 and not any other part of the string? why just the left hand char?

Thanks for the sprint pointer I will go read

Nigel

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nigelf
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Posted by nigelf: Sun. Feb 2, 2014 - 03:28 PM
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clawson wrote:
But you are already doing SD/FAT which already costs 20-30K so the odd extra 1-2K doesn't really matter does it?

once the images are on the LCD I reprogram the Arduino to a different program and use UTFT library to access the stored icons and fonts so save memory and speed that way though, im not sure how much of either.

Nigel

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larryvc
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Posted by larryvc: Sun. Feb 2, 2014 - 07:45 PM
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nigelf wrote:
why would it increment the 0 and not any other part of the string? why just the left hand char?
If you were using this
IMAGE_FILENAME[0]=IMAGE_FILENAME[0]++;

it is because you told it to.

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mikech
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Posted by mikech: Sun. Feb 2, 2014 - 09:32 PM
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char IMAGE_FILENAME[] = "0.CTE";

sets the size of that array to 6 bytes, so that will limit you to a single digit filename 0 .. 9

Quote:
why would it increment the 0 and not any other part of the string? why just the left hand char?
Because the string is just a sequence of bytes, changing one byte does not modify the other bytes.

sprintf() will probably be the simplest method, eg

char IMAGE_FILENAME[7];
int next_filenumber = 0;
...
sprintf( &IMAGE_FILENAME[0], "%d.CTE", next_filenumber );   /// create the filename
...
filenumber ++;   // increment to next file

which will let you do 0 .. 99

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Bronze Marktheusch
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Posted by theusch: Sun. Feb 2, 2014 - 10:39 PM
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Quote:

why just the left hand char?

Ummm--because >>your code<< told it to do that?

Quote:

IMAGE_FILENAME[0]=IMAGE_FILENAME[0]++;

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nigelf
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Posted by nigelf: Mon. Feb 3, 2014 - 01:11 AM
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ok I admit I am real slow! thanks guys I just made the connection it says increment the 0 part of the string. dam ! again thanks.

.... im off to eat some humble pie :)

Nigel

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christop
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Posted by christop: Mon. Feb 3, 2014 - 05:54 AM
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I'm a little surprised that nobody has mentioned that this code exhibits undefined behavior:

IMAGE_FILENAME[0]=IMAGE_FILENAME[0]++;

You cannot modify the same object more than once between sequence points. In this case, does the object get modified by the increment first or by the assignment first? The C standards don't say, and the compiler can do anything with that statement because it's undefined. A different compiler, or a different version of the same compiler, or even simply different compile options, may result in different behavior.

Of course, that's moot if you use a different method to increment your file names.

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Torby
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Posted by Torby: Mon. Feb 3, 2014 - 03:02 PM
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Just look at an ascii chart. Each character is represented by a number. '9' is 57. Add 1 to 57 to get 58, and that's a colon ':'.

http://www.asciitable.com/

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