Segfault during a call to fopen

[divc]

Hi all,
I've written a C program. I need to write some data into files. I've written some code and I'm getting a segmentation fault during a call to the fopen function. I've given part of the code here.

FILE *fp ;
/* ---
---
Some code here
---
--- */
/* Check for existence of file */
fname = strdup("Host");
strcat (fname , server_address) ;
strcat (fname , ".txt") ;
exist = access(fname , F_OK) ;

/*If it doesn't exist, create a new one */
if (exist == -1)
{
fp = fopen(fname , "w") ;
if (fp == NULL)
{
printf ("\nCannot open file\n") ;
return ;
}
else
{
fprintf (fp , "%s %s %s %s %s\n" , inf , ib , ob , ie , oe) ;
fclose(fp) ;
}
printf ("\n\nThe program has to be run once again for performing the necessary calculations.\n \n") ;
return ;
}
/* ---
---
Program continued
----
----
*/

As u can see, i've checked if fopen returns null. I can't figure out why this is happening. Can anyone help me?

[dasarath mood]

what is fname..???
have u allocated enough memory for fname..????
check once memory issues...

Hi all,
I've written a C program. I need to write some data into files. I've written some code and I'm getting a segmentation fault during a call to the fopen function. I've given part of the code here.

FILE *fp ;
/* ---
---
Some code here
---
--- */
/* Check for existence of file */
fname = strdup("Host");
strcat (fname , server_address) ;
strcat (fname , ".txt") ;
exist = access(fname , F_OK) ;

/*If it doesn't exist, create a new one */
if (exist == -1)
{
fp = fopen(fname , "w") ;
if (fp == NULL)
{
printf ("\nCannot open file\n") ;
return ;
}
else
{
fprintf (fp , "%s %s %s %s %s\n" , inf , ib , ob , ie , oe) ;
fclose(fp) ;
}
printf ("\n\nThe program has to be run once again for performing the necessary calculations.\n \n") ;
return ;
}
/* ---
---
Program continued
----
----
*/

As u can see, i've checked if fopen returns null. I can't figure out why this is happening. Can anyone help me?

[yogesh_anand]

Hi
I tried ur program.Might be u r not creating fname properly.Better new up memory for fname and do forgot to delete in end.
Where u r using strcpy ,use strncpy() func.

i tested ur program like this...It's running fine...

#include<iostre am>
#include<fstrea m.h>
using namespace std;
void main()
{
FILE *fp ;
int exist;
char *fname=new char[30];
char *server_address =new char[4];
strncpy(server_ address,"mib",4 );
/* Check for existence of file */
fname = strdup("Host");
strcat (fname , server_address) ;
strcat (fname , ".txt") ;
exist = access(fname , F_OK) ;

/*If it doesn't exist, create a new one */
if (exist == -1)
{
fp = fopen(fname , "w") ;
if (fp == NULL)
{
printf ("\nCannot open file\n") ;
return ;
}
else
{
fprintf (fp , "hi hi hi hi hi\n" ) ;
fclose(fp) ;
}
printf ("\n\nThe program has to be run once again for performing the necessary calculations.\n \n") ;
return ;
}
}
~

Hi all,
I've written a C program. I need to write some data into files. I've written some code and I'm getting a segmentation fault during a call to the fopen function. I've given part of the code here.

FILE *fp ;
/* ---
---
Some code here
---
--- */
/* Check for existence of file */
fname = strdup("Host");
strcat (fname , server_address) ;
strcat (fname , ".txt") ;
exist = access(fname , F_OK) ;

/*If it doesn't exist, create a new one */
if (exist == -1)
{
fp = fopen(fname , "w") ;
if (fp == NULL)
{
printf ("\nCannot open file\n") ;
return ;
}
else
{
fprintf (fp , "%s %s %s %s %s\n" , inf , ib , ob , ie , oe) ;
fclose(fp) ;
}
printf ("\n\nThe program has to be run once again for performing the necessary calculations.\n \n") ;
return ;
}
/* ---
---
Program continued
----
----
*/

As u can see, i've checked if fopen returns null. I can't figure out why this is happening. Can anyone help me?

[divc]

fname is a character pointer. I've initialized it as char *fname = NULL. Now, if i use fname = malloc(sizeof(c har[30])) in my program as suggested above, the program works just fine. But the issue here is that I've used other strings in the program and i've not explicitly used malloc. I've only used strdup("") during initialization. I didn't have any problems with those other variables. Y am i having a memory problem with this one ?

[yogesh_anand]

Hi

You have declare poniter fname and intial it also.But u haven't allocated memory for that one.Thats why it's coring.Intial pointer to null allocate memory for it also.Either using new or malloc it's up to u.
Once u will intial sufficient or appropriate memory blocks it will not going to core(as shown by me in sample program).
After that u can use strdup or strncpy.I will suggest strncpy.

fname is a character pointer. I've initialized it as char *fname = NULL. Now, if i use fname = malloc(sizeof(c har[30])) in my program as suggested above, the program works just fine. But the issue here is that I've used other strings in the program and i've not explicitly used malloc. I've only used strdup("") during initialization. I didn't have any problems with those other variables. Y am i having a memory problem with this one ?

[dasarath mood]

you malloc() a limited buffer using strcat(), but if the string is longer than u allocated memory for fname, the buffer will not be big enough. use strncat, and calculate the remaining space for the strncat() appropriately every time .

u will not get any problem after this.always use strncat ,it solves memory problems.