I having a problem with the following. Why doesn't this work ?
when i run this, its segfaults.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; }
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...
Or if you really want a pointer to a structure,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; }
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; }
Last edited by kmess; 04-25-2011 at 03:12 PM. Reason: Fixed the added code!.
sweet, thanx!
Glad it helped.
This time you forgot to allocate memory...
(LOL... stuff happens.)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; }
*blush* - I caught it, but evidently not fast enough! I was editing it the same time you were writing about it!
Kevin
LOL... Stuff happens!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!
Kevin
