segmentation fault writing to a struct using strncpy

[lurch132002]

i am trying to create an array of structs to hold some information but
whenever i get
to the second element and try to strncpy it i get a segmenation
fault. ive searched around for
similar problems but i cant seem to figure out what im doing wrong.
any help would be appreciated.

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

struct filesys {
char *fname;
int cylinder;
int sector;
int length;
};

int main( int argc, char *argv[] ) {

struct filesys file_array[100];

int i;
for( i = 0; i < 100; i++ )
strncpy(file_array.fname, "hello", 6);

for(i = 0; i < 100; i++ )
printf("%s", file_array.fname);
}

 

[Ian Collins]

i am trying to create an array of structs to hold some information but
whenever i get
to the second element and try to strncpy it i get a segmenation
fault. ive searched around for
similar problems but i cant seem to figure out what im doing wrong.
any help would be appreciated.

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

struct filesys {
char *fname;
int cylinder;
int sector;
int length;
};

int main( int argc, char *argv[] ) {

struct filesys file_array[100];

int i;
for( i = 0; i < 100; i++ )
strncpy(file_array.fname, "hello", 6);

Try allocating some memory for fname before you attempt to write to it!

 

[Peter Nilsson]

i am trying to create an array of structs to hold some
information but whenever i get to the second element and
try to strncpy it i get a segmenation fault. ive searched
around for similar problems but i cant seem to figure out
what im doing wrong.
any help would be appreciated.

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

struct filesys {
char *fname;

This declares a pointer only. It doesn't delcare what the
pointer points to. Writing through an uninitialised or null
pointer invokes undefined behaviour.

Try...

char fname[6];

int cylinder;
int sector;
int length;

};

int main( int argc, char *argv[] ) {

struct filesys file_array[100];

int i;
for( i = 0; i < 100; i++ )
strncpy(file_array.fname, "hello", 6);

Why are you using strncpy?

for(i = 0; i < 100; i++ )
printf("%s", file_array.fname);

The strncpy function was designed for fixed width fields.
Those fields need not be null terminated strings. If you
want to print such a field, then you should specify the
width so that printf doesn't overrun the field.

printf("%.6s", file_array.fname);

 

[lurch132002]

Thanks for the help guys, got it working once i changed fname the
pointer to fname the char array.

 

[Ian Collins]

(e-mail address removed) wrote:

Please quote enough context for your reply to make sense.

Thanks for the help guys, got it working once i changed fname the
pointer to fname the char array.

Make sure the array is large enough.