fopen() and open()

hi all,

i have a question,
whats the big difference between fopen() and open()?
what are the pro's and con's of both functions,

because you can open/wite/read files with both of them..
I find open() slightly harder to use then fopen().
But is it that open is UNIX/Linux only and fopen works on both?

thanks in advance

enrypted

Function fopen() opens a file and returns a pointer to FILE. You need to include stdio.h for it.

FILE *fopen (const char * restrict filename, const char * restrict mode);

Function open() is not a standard C function. It is a system call to open a file or device. To use it, you must include fcntl.h. But since it is not a standard C function, it may not be available in your system. Unix-like systems usually have it.

int open(const char *path, int flags, ...);

The pro of using fopen() is that it is standard.

Ok, thanks

so the bottom line is; fopen() is standard
open() is a UNIX system call


encrypted

open has a lot of extra features. Check that man page (only if you're able to use it of course)

Ok thanks,

but i have a problem now:

Code:

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
        int fd1, fd2;
        char *buffer;

        fd1 = open( "dude.dat", O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR );

        fd2 = open( "dude.dat", O_RDONLY );

        write( fd1, "UNIX", 5 );

        read( fd2, buffer, 5 );

        printf("%s\n", buffer );

        close( fd1 );
        close( fd2 );

        exit(0);
}

If i compile this code ( with gcc ) and run it, i dont get 'UNIX' on my screen but some weird characters that i've never seen before


Anyone know what im doing wrong?

thank you

encrypted

First, always perform error-checks. Check if the value that function open() returns is no error-value. In case open() returns an error-value, you cannot use that file-descriptor.

Second, you try open the same file twice. Try an algorithm like this:

- open the file for writing
- write to it
- close the file
- open the file for reading
- read from it
- close the file

Thanks man

i got it working,
and btw is this what you suggested by error checking? :

Code:

#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>

int main()
{
        int fd;
        char buffer[5];

        if( ( fd = open( "data.dat", O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR ) ) != -1 )
        {
                write( fd, "UNIX", 5 );
        }
        else
        {
                printf("File could not be opened");
                exit(1);
        }

        close( fd );

        if( ( fd = open( "data.dat", O_RDONLY ) ) != -1 )
        {
                read( fd, buffer, 5 );
        }
        else
        {
                printf("File could not be read");
                exit(1);
        }

        close( fd );

        printf("Result read from file:\n %s\n", buffer );

         exit(0);
}

encrypted

Yes that is what I meant with error-checking. A lot of standard functions return a specific value when an error occurred, checking the return values and take the right action when an error occurred results in more robust programs. When you don't perform error-checking, it is the same as assuming everything will always go right, which may result in undesirable behaviour of the code. Using error-checking you correct such behaviour.

[edit]
BTW, using function exit() is not necessary here. You could just use return 0 and return 1.
[/edit]

>>read( fd, buffer, 5 );
Unlike fgets(), read() won't terminate the array with a nul byte, so doing this might produce strange results:
>>printf("Result read from file:\n %s\n", buffer );

If you want to print the array as a string, make sure its nul terminated first.