dup() Post: 302259460

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Top Forums Programming dup() Post 302259460 by joey on Tuesday 18th of November 2008 07:02:44 AM

11-18-2008

Registered User

I have tried dup by itself in a little program its working. But when am using it in my original program its hanging...

Code:

// included everything needed. sys/types.h fcntl.h ...
int in, out, out1;

int doable(char Buffer[], char *args[], int *back_ground)
{
         //------watever here...

           // length is length of the Buffer.
           for(i = 0; i<length;i++)
           {
                   switch(Buffer[i])
                   {
                          case '>':
                              argument[0] = &Buffer[i+2];//consider &buffer[i+1] space . the user will write ls > myfile
                              out = open (argument[0] , O_WRONLY 
O_CREAT);
                              dup2(out,1);
                              i = length+1;
                   }
              }
}



int main()

{
int x1 = 0;
int back_ground = 0;
while(1)
{
      x1 = doable(Buffer, arguments, &back_ground)
      child = fork()
      if(child == 0)
      {      // i call execvp
       }
      else
       {
               // if backgroun or not.and i do the wait..and return if no error from execvp.(i       use       waitpid)
        }

// after both parent & child finish
       close(out);
      printf("new command line");
}}

The program is working with me without adding the dup and stuff.But after I added the dup & stuff..Whenever I run command ls > myfile ...the program hangs..and in my file nthg is printed...

Last edited by joey; 11-18-2008 at 08:09 AM..

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dup

dup(2)								System Calls Manual							    dup(2)

NAME

       dup - duplicate an open file descriptor

SYNOPSIS

DESCRIPTION

       fildes  is  a file descriptor obtained from a or system call.  returns a new file descriptor having the following in common with the origi-
       nal:

	      o  Same open file (or pipe).

	      o  Same file pointer (i.e., both file descriptors share one file pointer).

	      o  Same access mode (read, write or read/write).

	      o  Same file status flags (see fcntl(2),

       The new file descriptor is set to remain open across system calls.  See fcntl(2).

       The file descriptor returned is the lowest one available.

RETURN VALUE

       Upon successful completion, the file descriptor is returned as a non-negative integer.  Otherwise, a value of -1 is returned and is set	to
       indicate the error.

ERRORS

       fails if one or more of the following is true:

	      fildes	     is not a valid open file descriptor.

	      Request violates the maximum number of open file descriptors.

AUTHOR

       was developed by AT&T and HP.

SEE ALSO

       close(2), creat(2), dup2(2), exec(2), fcntl(2), open(2), pipe(2), privileges(5).

STANDARDS CONFORMANCE

																	    dup(2)

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