RE: problem in open sys call

RE: problem in open sys call

[Huber, George K RDECOM CERDEC STCD SRI]

Hi,

Try this:

	if((fd=open(opcode, O_RDONLY))==-1)
      {
	  printf("Open failed, error code: %d\n%s\n", errno, strerror(errno)
      }
		
you may need to add errno.h and string.h to the list of includes.  This will
give you the error code and desctiption of why open is failing.

George Huber
SRI, International

-----Original Message-----
From: linux-c-programming-owner@vger.kernel.org
[mailto:linux-c-programming-owner@vger.kernel.org]On Behalf Of joy
Sent: Tuesday, April 20, 2004 2:32 PM
To: linux-c-programming@vger.kernel.org
Subject: problem in open sys call


Hi,
I have a small prblem i the open call. it fails every time and I dont 
know why.

thanx in advance,
Joy.M.M

Re: problem in open sys call

[joy]

Huber, George K RDECOM CERDEC STCD SRI wrote:

 >Hi,
 >
 >Try this:
 >
 >	if((fd=open(opcode, O_RDONLY))==-1)
 >      {
 >	  printf("Open failed, error code: %d\n%s\n", errno, strerror(errno)
 >      }
 >		
 >you may need to add errno.h and string.h to the list of includes. 
This will
 >give you the error code and desctiption of why open is failing.
 >
 >
thanks a lot, george but I think Glynn hit the nail on the head. the
code was working fine before I added the opcode variable in main
and totlly neglected to see it while gdb'ing.

 >George Huber
 >SRI, International
 >
 >-----Original Message-----
 >From: linux-c-programming-owner@vger.kernel.org
 >[mailto:linux-c-programming-owner@vger.kernel.org]On Behalf Of joy
 >Sent: Tuesday, April 20, 2004 2:32 PM
 >To: linux-c-programming@vger.kernel.org
 >Subject: problem in open sys call
 >
 >
 >Hi,
 >I have a small prblem i the open call. it fails every time and I dont
 >know why.
 >
 >thanx in advance,
 >Joy.M.M
 >-
 >To unsubscribe from this list: send the line "unsubscribe 
linux-c-programming" in
 >the body of a message to majordomo@vger.kernel.org
 >More majordomo info at  http://vger.kernel.org/majordomo-info.html
 >
 >
 >

Re: problem in open sys call

[Holger Kiehl]

On Wed, 21 Apr 2004, joy wrote:

> Huber, George K RDECOM CERDEC STCD SRI wrote:
> 
> >Hi,
> >
> >Try this:
> >
> >      if((fd=open(opcode, O_RDONLY))==-1)
> >      {
> >        printf("Open failed, error code: %d\n%s\n", errno, strerror(errno)
> >      }
> >      >you may need to add errno.h and string.h to the list of includes. This
> will
> >give you the error code and desctiption of why open is failing.
> >
> >
> thanks a lot, george but I think Glynn hit the nail on the head. the
> code was working fine before I added the opcode variable in main
> and totlly neglected to see it while gdb'ing.
> 
But George and others also made a good point. With programming it is always
good practice to write good error messages and always try to be more
verbose. Believe me this can save you a lot of time! I even go so far
to always print out __FILE__ and __LINE__, so I know exacly where the
error has happened.

Holger

problem in open sys call

[joy]

[-- Attachment #1: Type: text/plain, Size: 112 bytes --]

Hi,
I have a small prblem i the open call. it fails every time and I dont 
know why.

thanx in advance,
Joy.M.M

[-- Attachment #2: opgen.c --]
[-- Type: text/plain, Size: 1021 bytes --]


#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>

const char opcode[]="opcode.sheet";
const char target[]="opcode.sheet";

main()
{
	char buff[8192],temp[10],bin=0,opcode[3];
	int fd,fd1,bytes_read=8192,count,i=0,inter_count=0;
	int offset=0,j=0,tempy;
	char head[]="OPCODE SHEET";
	
	if((fd=open(opcode, O_RDONLY))==-1)
		printf("oops");
	if((fd1=open(target, O_RDWR|O_CREAT))==-1)
		printf("O");
	while(bytes_read==8192)
	{
	bytes_read=read(fd,buff,8192);
	while(inter_count<bytes_read)
	{
		i=0;
		do
		{
			bin=buff[inter_count];
			temp[i]=buff[inter_count];
			inter_count++;
			i++;
		}while(bin!=10);
		temp[i++]=0;
		j=0;
	write(fd1,head,sizeof(head));
		for(j=0;j<i;j++)
		{
			tempy=(int)(temp[j]-0);
			offset+=tempy;
		}
		if(lseek(fd1,offset,SEEK_SET)==-1)
			printf("HI");
		
		printf("%s : ",temp);
		scanf("%s",opcode);
	      write(fd1,opcode,sizeof(opcode));
		printf("%s %d \n",temp ,offset);
	}
	}
	return(0);
}

Re: problem in open sys call

[Glynn Clements]

joy wrote:

> I have a small prblem i the open call. it fails every time and I dont 
> know why.

> const char opcode[]="opcode.sheet";

> 	char buff[8192],temp[10],bin=0,opcode[3];
==>	                               ^^^^^^

> 	if((fd=open(opcode, O_RDONLY))==-1)
> 		printf("oops");

In the open() call, the variable "opcode" refers to the local variable
of that name, which will be uninitialised, and not the global variable
which actually contains your filename.

Running your program under strace or a debugger would show that the
filename which is passed to open() isn't what you are expecting.

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: problem in open sys call

[joy]

Glynn Clements wrote:

>joy wrote:
>
>  
>
>>I have a small prblem i the open call. it fails every time and I dont 
>>know why.
>>    
>>
>
>  
>
>>const char opcode[]="opcode.sheet";
>>    
>>
>
>  
>
>>	char buff[8192],temp[10],bin=0,opcode[3];
>>    
>>
>==>	                               ^^^^^^
>
>  
>
>>	if((fd=open(opcode, O_RDONLY))==-1)
>>		printf("oops");
>>    
>>
thanks a lot, Glynn. I seem to be learning so much but must have 
somehow  missed the commonsense classes!

>In the open() call, the variable "opcode" refers to the local variable
>of that name, which will be uninitialised, and not the global variable
>which actually contains your filename.
>
>Running your program under strace or a debugger would show that the
>filename which is passed to open() isn't what you are expecting.
>
>  
>

Re: problem in open sys call

[Steven Smith]

[-- Attachment #1: Type: text/plain, Size: 407 bytes --]

> I have a small prblem i the open call. it fails every time and I dont 
> know why.

> const char opcode[]="opcode.sheet";
> 
> main()
> {
> 	char buff[8192],temp[10],bin=0,opcode[3];
Umm... did you mean to hide the global opcode behind a local which
never gets initialised?

Also, you may want to look at the man pages for:

errno(3)
err(3)
strerror(3)
gdb(1)
strace(1)

Steven Smith.

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Re: problem in open sys call

[Vadiraj C S]

 Best way to avoid this problems, effecient use of printf's and yes GDB would 
have solved your prblem then.

> 
> 	if((fd=open(opcode, O_RDONLY))==-1)
> 		printf("oops");

 Instead of printf("oops") go with perror(3) will prints cause of the error of the function 
like this.


 if ( ( fd = open (opcode, O_RDONLY ) ) == -1 )
 	perror("open Failed:");

 this will print the error message prefixed with your message "open Failed" 

 man perror for manual.

Cheers,

-- 

With Best Regards
 Vadiraj C S