Read letters from text

[strsh]

Greeting.
I am interested in how I can read a letter in a specific place in the text.
for example:
text is "SD card is initialized"
i want to assign the variable letter by letter and know where it is.
I thank in advance.

[dluu13]

What code have you written so far? It is always best to provide some source code so we can have a starting point to see if you are even thinking about the problem in the right way.

But from the most general position, a string is an array of characters so

[strsh]

This is my code:

[dluu13]

Which string are you attempting to manipulate specifically?

Can you give an example input, and the desired output?

For now, I suggest looking up strchr()
https://www.tutorialspoint.com/c_standard_library/c_function_strchr.htm

strchr() returns the pointer to the first occurrence of a character you specify.

Another function that may be useful to you is strcspn()
https://www.tutorialspoint.com/c_standard_library/c_function_strcspn

strcspn() returns the index of the first occurrence of a character contained in a string you specify.

[Ttelmah]

Before we talk about strings, there are significant issues with your
settings.

You have the fuse HSPLL, which says to use an external crystal with the PLL.
Yet you then have the clock setting trying to use the internal oscillator.
You have the clock speed set to 48MHz, which is not a speed available
from the internal oscillator on this chip.
So your serial will not be working.

Do you have a crystal?.
What frequency if so?.
Understand the PIC18F4550, cannot run it's USB without a crystal.

If you are using the internal oscillator, you need to simply use:

#use delay(internal=8MHz)

Which is the fastest speed available from the internal oscillator on this chip.

Look at the data sheet. The 'clock diagram'. Realise there is no connection
from the internal oscillator to the PLL. This is because the PLL on this
chip is primarily designed to drive the USB, and the internal oscillator
is not accurate enough to do this. So the manufacturer does not give this
connection....

Then there is a second (huge) issue. The 18F4550, is a 5v PIC. It will
_require_ level translation hardware to talk to an SD card. Read
the 'sticky' at the top of the forum about connecting to an SD card.

[strsh]

My mistake. I put the code wrong. Crystal is an external 8MHz. I don't use USB but I read the SD card. It contains the file "cnc.txt" and the file contains text eg "123456789 etc". I supply the PIC with 3.3V and I have no problem reading the entire text from the SD card, but I want to decompose the text and know where it is in the text.

[Ttelmah]

Seriously change PIC's.

The F4550, is rated to run at 4.2v _minimum_.
You are asking for failures particularly when the temperature rises
trying to run the PIC outside it's specification this far.

[dluu13]

About voltage, you should be able to just get a LF version of your processor and drop it right in

[strsh]

I know that the power supply is less than its minimum, but with that voltage I can read the SD card and read the text inside it into a variable called text. When I do the final version I will pay attention to it. Thanks for the suggestions.
My question is: How to parse variable text? Letter by letter.

dluu13
strchr () and strcspn () are for comparing (finding) letters in words and I do not need this because I do not know what I will have in the text. If you have an example with these commands, then write it to me. I would be grateful.

[temtronic]

Seriously, get a proper PIC, quick !
Just because, today, you can read the SD card is NO guarantee the PIC will actually operate and function 100%, an hour from now let alone tomorrow !! Add some minor hardware, add more code and the PIC will crash (good news) or worse randomly work OK then 'errors' occur (bad news).

Also if you need USB remember that 1/3rd of the PIC's program space will probably be filled with the USB driver code. Unless your main() program is very small, you can easily run out of code space ! BTDT...It only costs me $1 more to buy and use a TTL<>USB module. They've always worked for me, no USB driver needed, so you save a LOT of code space. AS well nearly ANY 1 or 2 pins can be used for 'USB' interfacing.

Jay

[strsh]

I have this module (purchased via aliexpress) and have worked with it. If I include a USB connection, I'll use it. Thanks for the suggestion. But I still have a problem decomposing the text variable. Any suggestions?

[dluu13]

But you must be looking for something in the text. Do you have a list of keywords you are looking for? You should read string.h header file yourself and try and find the functions you can put together to help you parse your text.

Besides, the two links I sent you have clear examples about how the functions work. You can follow the site directory back and it will show a listing of all the functions in string.h, with a similarly detailed example for each one.

[strsh]

I know what I'm looking for in the text, but it's important that I find it in a certain order and I'm sure nothing is skipped. I think the safest reading of the text is letter by letter (as we read it) and I can conclude what the word is.

Obviously I don't see what you see. I probably don't have enough knowledge. I know this forum does not like to require finished code, but I have no knowledge to see what I need to see. Help.

[dluu13]

Even if you provide an example of a text file, and then explain what the text in the file means in your application, and then how you want to process it, then we can help you much better. At this point, I don't know what you are looking for...

But if you really want to read it character by character, then you can do something like:

[strsh]

Thanks for the example. I'll try it on Monday and let you know if everything's okay.
Greeting.