05-23-2007
terminal device control through a C/C++ program
Hi,
I want to fork a new process from a daemon that needs terminal attachment to some ttyN or pts/N device. Here is the code
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <string.h>
int main(int argc, char **args)
{
char *con = args[1];
printf("\nStart demonizing ...\n");
int i = fork();
if (i == 0)
{
close (0);
close (1);
close (2);
setsid();
int j = fork();
if (j == 0)
{
setsid();
//int in = open(con, O_RDWR);
int in = open(con, O_RDONLY);
int ou = open(con, O_WRONLY);
dup2(in, fileno(stdin));
dup2(ou, fileno(stdout));
dup2(ou, fileno(stderr));
printf("\n input :");
stdin = fdopen(0, "r");
stdout = fdopen(1, "w");
stderr = fdopen(2, "w");
char tmp[100];
strcpy(tmp, "");
//gets(tmp);
fread(tmp, sizeof(tmp), 1, stdin);
printf("\n output : %s\n", tmp);
}
exit(0);
}
}
The program takes a single command line argument - the name of the terminal device special file, in my case that will be /dev/"pts/1". The problem is that, the inner most spawned child does the output on the pts/1 terminal successfully, but it fails to take input from it.
Anyone can help here.
Last edited by ku@ntum; 05-23-2007 at 08:28 AM..
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STDIO(3S) STDIO(3S)
NAME
stdio - standard buffered input/output package
SYNOPSIS
#include <stdio.h>
FILE *stdin;
FILE *stdout;
FILE *stderr;
DESCRIPTION
The functions described in section 3S constitute a user-level buffering scheme. The in-line macros getc and putc(3S) handle characters
quickly. The higher level routines gets, fgets, scanf, fscanf, fread, puts, fputs, printf, fprintf, fwrite all use getc and putc; they can
be freely intermixed.
A file with associated buffering is called a stream, and is declared to be a pointer to a defined type FILE. Fopen(3S) creates certain
descriptive data for a stream and returns a pointer to designate the stream in all further transactions. There are three normally open
streams with constant pointers declared in the include file and associated with the standard open files:
stdin standard input file
stdout standard output file
stderr standard error file
A constant `pointer' NULL(0) designates no stream at all.
An integer constant EOF (-1) is returned upon end of file or error by integer functions that deal with streams.
Any routine that uses the standard input/output package must include the header file <stdio.h> of pertinent macro definitions. The func-
tions and constants mentioned in sections labeled 3S are declared in the include file and need no further declaration. The constants, and
the following `functions' are implemented as macros; redeclaration of these names is perilous: getc, getchar, putc, putchar, feof, ferror,
fileno.
SEE ALSO
open(2), close(2), read(2), write(2), fread(3S), fseek(3S), f*(3S)
DIAGNOSTICS
The value EOF is returned uniformly to indicate that a FILE pointer has not been initialized with fopen, input (output) has been attempted
on an output (input) stream, or a FILE pointer designates corrupt or otherwise unintelligible FILE data.
For purposes of efficiency, this implementation of the standard library has been changed to line buffer output to a terminal by default and
attempts to do this transparently by flushing the output whenever a read(2) from the standard input is necessary. This is almost always
transparent, but may cause confusion or malfunctioning of programs which use standard i/o routines but use read(2) themselves to read from
the standard input.
In cases where a large amount of computation is done after printing part of a line on an output terminal, it is necessary to fflush(3S) the
standard output before going off and computing so that the output will appear.
BUGS
The standard buffered functions do not interact well with certain other library and system functions, especially vfork and abort.
LIST OF FUNCTIONS
Name Appears on Page Description
clearerr ferror.3s stream status inquiries
fclose fclose.3s close or flush a stream
fdopen fopen.3s open a stream
feof ferror.3s stream status inquiries
ferror ferror.3s stream status inquiries
fflush fclose.3s close or flush a stream
fgetc getc.3s get character or word from stream
fgets gets.3s get a string from a stream
fileno ferror.3s stream status inquiries
fopen fopen.3s open a stream
fprintf printf.3s formatted output conversion
fputc putc.3s put character or word on a stream
fputs puts.3s put a string on a stream
fread fread.3s buffered binary input/output
freopen fopen.3s open a stream
fscanf scanf.3s formatted input conversion
fseek fseek.3s reposition a stream
ftell fseek.3s reposition a stream
fwrite fread.3s buffered binary input/output
getc getc.3s get character or word from stream
getchar getc.3s get character or word from stream
gets gets.3s get a string from a stream
getw getc.3s get character or word from stream
printf printf.3s formatted output conversion
putc putc.3s put character or word on a stream
putchar putc.3s put character or word on a stream
puts puts.3s put a string on a stream
putw putc.3s put character or word on a stream
rewind fseek.3s reposition a stream
scanf scanf.3s formatted input conversion
setbuf setbuf.3s assign buffering to a stream
setbuffer setbuf.3s assign buffering to a stream
setlinebuf setbuf.3s assign buffering to a stream
sprintf printf.3s formatted output conversion
sscanf scanf.3s formatted input conversion
ungetc ungetc.3s push character back into input stream
4th Berkeley Distribution May 13, 1986 STDIO(3S)