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I am traing to read and then to write.
I don't know why but I have to write before reading.
It doesn't work this way:
HELP plz \:Code:FILE *in, *out;
int i, max;
in = fopen ("x.txt","rt");
if (in == NULL)
return 0;
for (max = fgetc(in);!feof(in);max += fgetc(in) * i)
i *= 10;
fclose(in);
"rt" should be "r". You should note that unless the file x.txt exists, then a call to fopen with trying to open a file for reading using "r" will fail.
Make sure the file exists first, then you can read first and write later.
humm I create the file manually before running the program..
Anyway how can I read the number from the file?
For example: 100
And why it's "r" and not "rt"?
Assuming we can expect the file to exist, you should use "r+" (the "t" in the mode would be a Microsoft extension, and it's default to be text anyways, so for compatibility, don't use it).
"r+" means that the file is read and write.
If you don't know if the file exists, but you still want to read from it (rather than just add to the end of it), you can use "a+". This sets the file-position to the end of the file, so you it needs to be combined with fseek() or rewind() to get to a different place than end-of-file.
--
Mats
Well, then it's likely you specified incorrect path. Try an absolute path and see if that works.Quote:
Originally Posted by gavra
I assume you just wrote 100 into notepad and saved the file?Quote:
Anyway how can I read the number from the file?
For example: 100
If so, then use fgets to read line and then strtod to convert into a integer (to store in an integer variable).
Ok, but if I want to create a file and the to read and maybe to write to what should I use?
strtol is better than strtod if you want to convert integer values. strtod stands for "String to Double", strtol is "String To Long Integer".Quote:
Originally Posted by Elysia
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Mats
"a+" combined with fseek() or rewind() [rewind(file) is the same as fseek(file, 0, SEEK_SET) - but I think some runtime libraries do not have rewind().]Quote:
Originally Posted by gavra
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Mats
Ho that's waht I need.. to convert into integer.Quote:
Originally Posted by Elysia
Can you explain me about "strtod" plz?
Or you just explain me about the "strtod"..
And how do I check if any file is exist?
Yes, of course, I tend to mix those two.Quote:
Originally Posted by matsp
Quote:
Originally Posted by gavra
To check if a file exist, open file with fopen. If fopen returns NULL, then it doesn't exist or you don't have permission to access that file.Code:char mystr[] = "100";
long n = strtol(mystr, NULL, 10);
If you want to know if the file exists, try opening for reading first, if that's not working, then open for writing instead (check status of this as well, could be that you can't open/create files for some other reason, e.g. you haven't got sufficient rights, the disk is a CDROM, so you can't create files, etc, etc).Quote:
Originally Posted by gavra
Alternativelys, if you use "a+", and use ftell() without fseek or rewind, if you get zero from ftell, then the file was just created (or at least, the file is empty - it could of course be an existing empty file, but for most intents and purposes, that's the same thing as no file).
strtol is what you want, since "max" is an integer, not a double.
http://www.hmug.org/man/3/strtol.php
--
Mats
thx.
Problem..
what now?Code:FILE *in, *out;
char str[15];
int max;
in = fopen ("x.txt","t");
if (in == NULL)
{
out = fopen("x.txt","w");
fclose (out);
}
fgets (str,15,in);
max = strtol (str,NULL,15);
printf("%d",max);
fclose(in);
That looks about right, so what do you want it to do that it's not currently doing?
Edit: What I'm trying to say is that you haven't explained what your overall goal is with your program. So it's not very easy for us to say what you should or shouldn't do within your code...
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Mats
It gives me a "report".
I'll say what I am traing to do so we all understand each other better.
I wrote a game today (feed the snake) and I want to save records.
First of all I want to check if the score is bigger then the last record.
If so I want to change the record (and maybe add a name too).
I have noticed that even though the file exist fopen returns NULL \:
So, what you are doing is a high-score list, yes?
If that's the case, then you need to essentially implement an "insertion sort". Inserting into a file is not possible, so if you want a limited high-score list (e.g. 10, 50 or 100 highest scores), then you should probably read all the current values in the file into an array [with 10, 50 or 100 elements, of course], then insert the new element and write all the data back to the file (after using fseek or rewind to get back to the beginning of the file).
Bear in mind that you will need to keep track of the number of entries, and discard the lowest one when the table is full.
If you want to keep all scores from today and forever after, then you will need a different approach, either store all results in the order they came, and then use a sorting or selection mechanism to find the entries you want. Or read from the original file, write to a new file (adding the new entry at the appropriate place, just before the entry that is smaller (if you want equal scores "newest first" then compare less or equal instead of less than)).
--
Mats
Are you sure you are opening the file in the same directoy as you think it is? use getcwd() to find what your application is actually using.Quote:
Originally Posted by gavra
http://www.hmug.org/man/3/getcwd.php
--
Mats
"t" is not a valid mode. It's either "r", "w" or "a", and a "+" can be added to form "r+" and "w+".
Second, read your logic there. If you fail to open a file, you must not try to read from it.
Trying to close an unopened file will also crash the program.
Read the documentation for strtol again. The last argument in the base.
thank you.
Yep that's what I am traing to do.
It's not that easy as I thought.
Same directory, I think.. and the function you give works like this: getcwd(*fp,size of what?) ?!
You right, it's just I havent play so many time with those things so I don't know them so well..Quote:
Originally Posted by Elysia
LOL I'am so fool XD
It works only if the file is exist.
I want it to create the file if it doesn't exist..Code:int read_write (int score)
{
FILE *in, *out;
char str[15];
int max;
in = fopen ("Highscore.txt","r+");
if (in == NULL)
{
out = fopen("Highscore.txt","w");
fputc ('0',out);
fclose (out);
in = fopen ("Highscore.txt","r+");
}
fgets (str,15,in);
max = atoi(str);
if (score > max)
{
printf ("\nNew Highscore!\n");
rewind (in);
fprintf (in,"%d",score);
}
fclose(in);
}
Thank again.
Again, this code is bad. Let me give you a scenario:
Try to open Highscore.txt. File does not exist. Fail.
Try to open Highscore.txt for writing. Insufficient permissions. Fail.
Write '0' to out. File is not open. Crash.
Close file which is not open. Fail. Crash.
Open Highscore.txt for reading. File does not exist. Fail.
Try to read a line from the Highscore.txt file. File is not open. Fail. Crash.
Atoi is still non-standard. Again, use strtol.
Score > max condition is true.
Print text "\nNew Highscore!\n"
Rewind input file to beginning. File is not open. Fail. Crash.
Print new highscore.
Close input file. File is not open. Crash.
To open a file for writing use "w", as you do. You may even open is at "w+" to open the file for writing (creating it if it doesn't exist) and for reading.
Thank's.
"Atoi is still non-standard. Again, use strtol."
I tried but it's complicated (so I use the simplest) I didn't understand the need of the 3 arguments and what means each of them.
If you only need the functionality of atoi when using strtol, you can do:Quote:
Originally Posted by gavra
strtol(number, NULL, 10);
You'll learn what the extra arguments are when you gain experience.