How to pull one character from file? 1

[GoAskAlice]

Gosh, this sounds so easy! But, I am having serious problems.

I wrote a file using fwrite to record 9 number sequences of 8 digits each in length. No seperators, just a long line of digits went into the file.

Now, I want to pull a single digit from the file using fread but it really wont let me do it.

I have set up an array;
int a[8];

to record 8 digits from the file.

I use;
readcount = fread(a,8,8,fp);

to read the numbers from the file.

This however, fills each array with 8 digit numbers. I have tried several different ways of doing this, such as changing the number 8 to 1, and so on, and all I get is garbage output.

I mean, I just want to be able to read 8 digits at a time from the file and have each digit indexed in an array so I can process it.

It really has got me because I also tried fgetc without any success...

Can some one PLEASE help!

 

[GoAskAlice]

#include <stdio.h>
#include <stdlib.h>
int main() {
FILE *fp;

char *s = "12345678";

long t = atol(s);

printf("%ld\n",t);

fp = fopen( "dbat", "w" );

fputc(*s,fp);

fclose( fp );

fp = fopen( "dbat", "r" );
int c;
int cnt = 0;
char buffer[8];
while (cnt < 8) {
c = fgetc( fp );

buffer[cnt++] = (char) c;

}

fclose( fp );


int cent = 0;
for(cent = 0; cent < 8; cent++) {


printf("%c",buffer[cent]);

}

/*
char *st = buffer;

t = atol(st);

printf("%ld\n",t);
*/

return 0;

}

This is the code I have gotten to so far.

The first print statement outputs;
12345678
The second outputs;
1???????

I dunno why? Someone give a brother a hand.

 

[Salem]

It's really hard to say what's going on with all that overuse of 8 in your code - where did that come from?

int a = 1;
int b = 12345678;
fwrite( &a, sizeof a, 1, fp );
fwrite( &b, sizeof b, 1, fp );

Assuming that sizeof(int)==4 on your machine, both result in 4 bytes being written to the file regardless of the stored value in the integer.

Likewise when you read the file, you read a whole int.

Reading a single byte is the equivalent of doing something like
[tt]int temp = a & 0xff;[/tt]
You get part of the number returned, not necessarily a single decimal digit (more like 2.5 decimal digits).

--

 

[GoAskAlice]

*smiles* @ over use of 8

Thanks for the info. It helps a little bit.

In fact, it was just now when I kinda figured it out. Using fgetc and fputc I was trying to input a whole string "12345678" (hence the 8's in code)

But like, I realised I am only inputting one char. When it came to reading the data back, I got only 1 char back.

Also, I figured out that I have to do multiple fputc in order to write string "12345678" to the file.

It makes total sense, but the material I am working from is not helping as it seems to tell me to do wrong.

 

[Salem]

Well if you want strings, that you can read and write a single character at a time, then you need to be using

fprintf( fp, "%d\n", myInt );
fscanf( fp, "%d", &myInt );
ch = fgetc( fp );

But with the printed form, you need some kind of whitespace between integers to tell them apart (unless all your ints are always 8 characters long).


--

 

[maur3r]

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
FILE *fp;
const char *s = "12345678";
long t = atol(s);
int c;
int cnt = 0;
char buffer[8];
int cent = 0;

printf("%ld\n",t);

fp = fopen( "dbat", "w" );
fputs(s,fp);
fclose( fp );

fp = fopen( "dbat", "r" );

while (cnt < 8) {
  c = fgetc( fp );
  buffer[cnt++] = (char) c;
}

fclose( fp );

for(cent = 0; cent < 8; cent++)
  printf("%c",buffer[cent]);
  printf("\n");


return 0;
}

Maybe it will help a bit. Hope you don't mind little rearrangments in code.

 

[GoAskAlice]

Hey, I cant express how happy that code example has made me.

Now I have a working example of fputs and fputc that actually does what it is supposed to do *big smiles*

See, I am trying to create a list of all the unique numbers within a range - its a long story - but when I tried to do it in PHP it would crash my computer. Sure, it would work with ranges 1 to 10, struggled with 16, and anything above would hang the machine. So, I had C in a Nutshell sitting on my bookcase for ages gathering dust, and decided to brush it off and have a bash at the program in C.

The part I am working on at the moment is conversions between char and int and returning a array from a function. I noticed I can return a pointer to an array but not the array itself.

I really want to get this program to work under Linux and then I will be trying to compile the same program under Windows XP. It'd be cool to have the program for both systems.

Thanks again maur3r.

 

[maur3r]

I´m glad that I could help.

Martin