Error using 'read', error 9. I must be blind

Hi. I'm a bit desesperated, Can you help me?

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

#define SIZE 1024

extern int error;

int main () {
        int file = open("lets.try", O_WRONLY|O_CREAT|O_TRUNC, 0666);

        unsigned char buffer[SIZE];
        memset (&buffer, 0xFF, SIZE);

        write(file, buffer, SIZE);

        lseek (file, SEEK_SET, 0);
        if (read(file, buffer, SIZE) == -1)
                printf ("\nERROR == %d :(\n\n", errno);


When this code is executed a file named "lets.try" is created with size == 1KB and plenty of '1's. But also the if condition is "trued", so it means there's have been an error reading the file. But... why? Why writing works and reading not? What am I missing?.

I've used errno variable to try to guess what's happening. As i've read value 9 means:

fd is not a valid file descriptor or is not open for reading.

But this has no sense because then that same file descriptor would be worng for write operation.

Mm.. I wish you can help me. I'm sure it's something stupid but I can't see it.

I've build the code in knoppix, xfld and Kubuntu. (All live versions). All are based on debian and same error on all.

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>  int file = open("lets.try", O_WRONLY|O_CREAT|O_TRUNC, 0666);

O_WRONLY  means "WRITE ONLY".  The file is opened for writing only, not reading.
If you want to both read and write the file, use O_RDWR rather than O_WRONLY.


    int file = open("lets.try", O_WRONLY|O_CREAT|O_TRUNC, 0666);

   The file lets.try has been opened in write-only mode (O_WRONLY). It's not opened for reading. So you have to change O_WRONLY with O_RDWR.
    Or you can close the file and open again for read-only(O_RDONLY).


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oops ...
  so its already answered.
KyroiiAuthor Commented:
Damn! So easy... I knew it was something stupid.

Thk u all.
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