RE: Fgets is not working on linux/gcc3.2.1

RE: Fgets is not working on linux/gcc3.2.1

[Ajay Bansal]

Problem was not that I _have_ to read a file somehow. Problem was.. How
do read using fgets.  & why it bbehaves differently on Solaris/Linux
with same compiler. 

If I open the file with "a+", the on Solaris file pointer is at the
beginning of the file whereas on Linux it is at the end of the file. Why
is this difference???

And if some code is already written using fgets on solaris, this
difference makes it non-portable!!!!!


-----Original Message-----
From: John Love-Jensen [mailto:eljay@adobe.com] 
Sent: Thursday, April 10, 2003 5:56 PM
To: Ajay Bansal; redhat-devel-list@redhat.com; gcc-help@gcc.gnu.org

Hi Ajay,

Why not do it C++ style, instead of co-mingling C and C++ styles?

Sincerely,
--Eljay

PS:  your data-type Hungarian notation is incorrect.  I strongly suggest
that you avoid date-type Hungarian notation, unless you are going to be
meticulously accurate.  (Otherwise it contributes to code obfuscation.)

PPS:  I also recommend on "using" the particular item in the other
namespace, instead of pulling in the whole namespace.

PPPS:  I also recommend using C++ headers, instead of pulling in C
headers into your C++ code.  (i.e., <cerrno> and <cstdlib>.)

---------------------

#include <iostream>
  using std::cout;
  using std::endl;
#include <fstream>
  using std::
#include <string>
  using std::string;
// #include <cerrno> -- not needed.
// #include <cstdlib> -- not needed.
int main()
{
    string fileName("/tmp/log.txt");
    string line;
    ifstream file(fileName.c_str());
    int lineNumber = 0;

    while (getline(file, line)) {
       ++lineNumber;
       cout << "Line " << lineNumber << " read is : " << line << endl;
    }

    return 0;
}

RE: Fgets is not working on linux/gcc3.2.1

[Bharathi S]

On Thu, 10 Apr 2003, Ajay Bansal wrote:

> If I open the file with "a+", the on Solaris file pointer is at the
> beginning of the file whereas on Linux it is at the end of the file.
> Why is this difference???

After opening the file, Just move the File pointer to the beginning of 
file. [ Nasty temp solution ] :)

I think, fopen may failed to conform to some Stds like ANSI, IEEE, 
POSIX ...

Thanks :)
-- 
Bharathi S, IndLinuX Team,  (__)
DON Lab,      TeNeT Group,  oo )
IIT-Madras, Chennai-INDIA.  (_/\

Re: Fgets is not working on linux/gcc3.2.1

[LLeweLLyn Reese]

"Ajay Bansal" <Ajay_Bansal@infosys.com> writes:

> Hi All
> 
> Following program is not working on linux. Ideally it should read all
> the lines from "/tmp/log.txt" and print them on to the screen. Instead
> it breals after it encounters fgets for the first time.
> 
> Pleas tell me where I am going wrong!!!! This program is working as
> expected on a Solaris machine.
> 
> Regards
> -Ajay
> ------------------------------------------------------------------------
> -----------
> 
> Entries in log.txt
> ------------------
> Line1
> Line2
> Line3
> ------------------
> 
> Output of the program
> ---------------------
> [ajay@linux1 test]$ ./a.out 
> Fileno is :3
> Error no is : 0
> Error is : Success
> Line read is : 
>  after fgets break outside while loop
> ---------------------
> 
> #include <iostream>
> #include <fstream>
> #include <errno.h>
> #include <stdlib.h>
> using namespace std;
> int main()
> {
>     char * pszFileName = "/tmp/log.txt";
>     char * pszMode = "a+";
>     char lpsz[4096];
>     FILE *pFile = fopen(pszFileName, pszMode);

      fseek(pFile,0,SEEK_BEG);

will fix your problem. On solaris, where a file opened with a is
    opened at the begining, the above will have no effect. On linux,
    where the file is opened at the end, the above will seek to the
    begining. 


> 
>     while (!feof(pFile)) {
>         if (! fgets(lpsz, 4096, pFile))
>         {
>             cout<<"Error no is : "<<errno<<endl;
>             cout<<"Error is : "<<strerror(errno)<<endl;
>             cout<<"Line read is : "<<lpsz<<endl;
>             break;
>          }
> 	   cout<<"Line read is : "<<lpsz<<endl; 
>     	   cout <<" after fgets break inside while loop"<<endl;
>     }
> 
>     cout <<" after fgets break outside while loop"<<endl;
> 
>     return 1;
> }

Re: Fgets is not working on linux/gcc3.2.1

[John Love-Jensen]

Hi Ajay,

Why not do it C++ style, instead of co-mingling C and C++ styles?

Sincerely,
--Eljay

PS:  your data-type Hungarian notation is incorrect.  I strongly suggest
that you avoid date-type Hungarian notation, unless you are going to be
meticulously accurate.  (Otherwise it contributes to code obfuscation.)

PPS:  I also recommend on "using" the particular item in the other
namespace, instead of pulling in the whole namespace.

PPPS:  I also recommend using C++ headers, instead of pulling in C headers
into your C++ code.  (i.e., <cerrno> and <cstdlib>.)

---------------------

#include <iostream>
  using std::cout;
  using std::endl;
#include <fstream>
  using std::
#include <string>
  using std::string;
// #include <cerrno> -- not needed.
// #include <cstdlib> -- not needed.
int main()
{
    string fileName("/tmp/log.txt");
    string line;
    ifstream file(fileName.c_str());
    int lineNumber = 0;

    while (getline(file, line)) {
       ++lineNumber;
       cout << "Line " << lineNumber << " read is : " << line << endl;
    }

    return 0;
}

RE: Fgets is not working on linux/gcc3.2.1

[Bharathi S]

On Thu, 10 Apr 2003, Ajay Bansal wrote:

> But then, would the behavior of fopen be different on 
> Soalris/Linux!!!!!!!!!

I am NOT an expert :) man fopen gives me the following infos :)

 "a" --  Open for writing.  The file is created if it does not 
         exist.  The stream is positioned at the end of the
         file.

"a+" --  Open for reading and writing.  The file is created if 
         it does not exist.  The stream  is  positioned  at the 
         end of the file.

The fopen and freopen functions conform to ANSI X3.159-1989 (``ANSI
C'').  The fdopen function conforms to IEEE Std1003.1-1988
(``POSIX.1'').

HTH :)
-- 
Bharathi S, IndLinuX Team,  (__)
DON Lab,      TeNeT Group,  oo )
IIT-Madras, Chennai-INDIA.  (_/\

RE: Fgets is not working on linux/gcc3.2.1

[Ajay Bansal]

But then, would the behavior be different on Soalris/Linux!!!!!!!!! 


-----Original Message-----
From: Bharathi S [mailto:bharathi@lantana.tenet.res.in] 
Sent: Thursday, April 10, 2003 12:15 PM
To: GNU GCC

On Thu, 10 Apr 2003, Ajay Bansal wrote:

> Following program is not working on linux. Ideally it should read all 
> the lines from "/tmp/log.txt" and print them on to the screen.
> Instead it breals after it encounters fgets for the first time.

File is opened in Append mode. Bcoz of this file pointer may positioned
in the end of file. 

Try it by opening in Read mode.

HTH :)
--
Bharathi S, IndLinuX Team,  (__)
DON Lab,      TeNeT Group,  oo )
IIT-Madras, Chennai-INDIA.  (_/\

Re: Fgets is not working on linux/gcc3.2.1

[Bharathi S]

On Thu, 10 Apr 2003, Ajay Bansal wrote:

> Following program is not working on linux. Ideally it should read
> all the lines from "/tmp/log.txt" and print them on to the screen.
> Instead it breals after it encounters fgets for the first time.

File is opened in Append mode. Bcoz of this file pointer may 
positioned in the end of file. 

Try it by opening in Read mode.

HTH :)
-- 
Bharathi S, IndLinuX Team,  (__)
DON Lab,      TeNeT Group,  oo )
IIT-Madras, Chennai-INDIA.  (_/\

Fgets is not working on linux/gcc3.2.1

[Ajay Bansal]

Hi All

Following program is not working on linux. Ideally it should read all
the lines from "/tmp/log.txt" and print them on to the screen. Instead
it breals after it encounters fgets for the first time.

Pleas tell me where I am going wrong!!!! This program is working as
expected on a Solaris machine.

Regards
-Ajay
------------------------------------------------------------------------
-----------

Entries in log.txt
------------------
Line1
Line2
Line3
------------------

Output of the program
---------------------
[ajay@linux1 test]$ ./a.out 
Fileno is :3
Error no is : 0
Error is : Success
Line read is : 
 after fgets break outside while loop
---------------------

#include <iostream>
#include <fstream>
#include <errno.h>
#include <stdlib.h>
using namespace std;
int main()
{
    char * pszFileName = "/tmp/log.txt";
    char * pszMode = "a+";
    char lpsz[4096];
    FILE *pFile = fopen(pszFileName, pszMode);

    while (!feof(pFile)) {
        if (! fgets(lpsz, 4096, pFile))
        {
            cout<<"Error no is : "<<errno<<endl;
            cout<<"Error is : "<<strerror(errno)<<endl;
            cout<<"Line read is : "<<lpsz<<endl;
            break;
         }
	   cout<<"Line read is : "<<lpsz<<endl; 
    	   cout <<" after fgets break inside while loop"<<endl;
    }

    cout <<" after fgets break outside while loop"<<endl;

    return 1;
}