Thread: Binary files

create a file

FILE * file;
file = fopen("filename.ext","wb"); //w for write b for binary

i think that right i mostly do the c++ way when working
with files so i dont remember if that correct or not.


to read from a file in binary i believe its

char ch;
file.fread((char*) ch, sizeof( ch ) ); //if that correct it read one character from the file.

wow i really dont remember c way of it at all c++ so much better

and to move aroudn in the file i believe the function is

fseek()

clearly i dotn remember the correct usage of some of these
function but all you need to do is google the function to
figure out how to use it.


as for manipulating data in the record, you would obviously
need to be fimilar with how the file looks inside,
either setup a certian outline for the data in the file, or
learn how to manipulate what already in there.
then you can read thru the data till you find a specific
record and there ya go.

sorry i couldnt be as detailed as i wanted to be, if
you change to c++ then holla at me and ill hoook you up

It's cool. I was trying your code out. In the meantime, I also seem to be having trouble with "fclose". Based on past experiences, I assume this means I'm probably having trouble with "fopen":

Code:

#include <stdio.h>

//prototypes
int start_binary (void);

int main (void)
{
    start_binary ()

    return (0);
}

int start_binary (void)
{
    FILE *fp = fopen ("prime_binary.txt", "wb");

    fclose (fp);

    if (!fp)
    {
        printf ("Close successful");

        return (0);
    }
    else
    {
        printf ("Close failed");
    }

    printf ("\n\n");
    return (0);
}

It compiles correctly, but the output I get is "Close failed". Does anyone know why I'm getting this?

mw

PS: An empty "prime_binary.txt" file was created by the program. So maybe my "if" statement is incorrect?

ive never see them check if a file had been closed before

also you should check this out

my guess on that would be, if the file had been closed correctly
it would prolly return a non-zero value, meaning
that it would return true, but since your doing the opposite,
( ! ), if it had come back true that it was closed, it would say false
and run the else statment. that just a guess though.

then again fp is a pointer right, so once the file
is closed id imagine that fp would be pointing at junk
iin memory, so i dont think taht the correct way of coing about it.


maybe this is a possiblity

if( fclose( fp ) )

liek i said c++ i so much awsomer :O

> Does this mean that I can open *any* text file as a binary file, assuming I correctly describe it to my program?
Yes.

What you should actually do is check the return value of fopen to see if it failed.

Code:

FILE *fp;
if((fp=fopen(filename, mode)) == NULL) {
    /* report error */
}

fclose cannot modify what fp points to. It can only modify what fp is pointing to. Therefore, fp must hold fopen()'s return value. In your code

Code:

int start_binary (void)
{
    FILE *fp = fopen ("prime_binary.txt", "wb");

    fclose (fp);

    if (!fp)
    {
        printf ("Close successful");

        return (0);
    }
    else
    {
        printf ("Close failed");
    }

    printf ("\n\n");
    return (0);
}

You're just checking if fopen failed. But you should check if fopen failed before you start using the filehandle.

ILoveVectors:

Code:

file.fread((char*) ch, sizeof( ch ) );

file is a structure. Also, the first argument is a void pointer, so no cast is required. fread takes three arguments, and is usually used in conjunction with fwrite (otherwise you tend to get gibberish).

Hmm... I seem to have more questions:

Code:

#include <stdio.h>

//prototypes
int start_binary (void);
void scope_test (void);

int main (void)
{
    start_binary ();

    return (0);
}

int start_binary (void)
{
    char x[10] = "ABCDEFGHIJ";
    FILE *fp = fopen ("prime_binary.txt", "wb");

    if (!fp)
    {
        printf ("\n\nERROR!  Not enough memory!\n\n");

        return (0);
    }

    fwrite (x, sizeof (x[0]), sizeof (x) / sizeof (x[0]), fp);

    scope_test ();

    fclose (fp);
    printf ("\n\n");
    return (0);
}

void scope_test (void)
{
    int loop = 0;
    char x[10] = "JIHGFEDCBA";

    FILE *fp = fopen ("prime_binary.txt", "a");

    for (loop = 0; loop < 10; loop++)
    {
        fprintf (fp, "%c", x[loop]);
    }

    fclose (fp);
}

(If there are any syntax errors, I apologize. I'm on a seperate computer and had to retype it here)

When I run this program:

1) Why doesn't Windows crash when I attempt to open a file twice (especially in different modes)?

2) Why do I only have 1 line instead of 2 in my text file after this program is finished running? I was trying to "append" in my scope_test function to see what would happen.

Thanks!

mw

> (If there are any syntax errors, I apologize. I'm on a seperate computer and had to retype it here)
I suggest you only post the code you try in future.

By the time you've posted what you think you have, we've responded to what we think you meant, you've taken away what you think we've said back to your other machine, the result is nothing like what you started with.

Originally Posted by Lionmane

Why didn't you answer my question? The next time you post a response to someone's question, try to be a little less inept at it.

Don't use big words you don't know the meaning of. You just look like an idiot trying to mimic Salem.

1) Show me in the standard where it says Windows has to crash because you call fopen twice on the same file.
2) What the hell did you expect? Why should it keep both of your changes when you open the file twice? How can that even remotely be correct? How on earth could you be so stupid as to think that is even remotely correct? Now you're surprised it doesn't work? What?


Quzah.