FILE within a structure

I having a problem with the following. Why doesn't this work ?

Code:

---

#include <stdio.h>

struct myfile {
  FILE * myPtr;
};

int main(int argc, char **argv)  {
  struct myfile *file;
  file->myPtr = fopen("myfile.txt","a");
 return 0;
}

---

when i run this, its segfaults.

You never allocate space for file. You just make a pointer to it, and that pointer is uninitialized, so file->myPtr is dereferencing invalid/unknown memory. You need to either malloc (and free) some memory, or make an actual struct and access the members with a . instead of a pointer to a struct using the -> operator.

This will compile...

Code:

---

#include <stdio.h>

struct myfile {
    FILE *myPtr;
};

int main( int argc, char **argv )
{
    struct myfile file;

    file.myPtr = fopen( "myfile.txt", "a" );
    fclose( file.myPtr );

    return 0;
}

---

Or if you really want a pointer to a structure,

Code:

---

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

struct myfile {
    FILE *myPtr;
};

int main( int argc, char **argv )
{
    struct myfile *file;

    file = ( struct myfile * )malloc( sizeof( struct myfile ) );

    if ( file != NULL ) {
        file->myPtr = fopen( "myfile.txt", "a" );
        /* do something */
        fclose( file->myPtr );
        free( file );
    }

    return 0;
}

---

sweet, thanx!

Glad it helped. :)

:D This time you forgot to allocate memory...

Code:

---

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

struct myfile {
    FILE *myPtr;
};

int main( int argc, char **argv )
{
    struct myfile *file;

    file = malloc(sizeof( struct myfile ));

    if ( file != NULL ) {
        file->myPtr = fopen( "myfile.txt", "a" );
        /* do something */
        fclose( file->myPtr );
        free( file );
  }
    return 0;
}

---

(LOL... stuff happens.)

*blush* - I caught it, but evidently not fast enough! I was editing it the same time you were writing about it! :tongue:

Kevin

Quote:

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Originally Posted by kmess

*blush* - I caught it, but evidently not fast enough! I was editing it the same time you were writing about it! :tongue:

Kevin

---

LOL... Stuff happens!