// This is my code for reading a file from command line arguments and storing it in another file.//
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h> //for system calls such as dup(),pipe(),etc...
#include <sys/wait.h>
#define COUNT_PROGRAM "b"
#define CONVERT_PROGRAM "c"
int main(int argc, char *argv[])
{
if (argc != 3)
{
fprintf(stderr,"%s","ERROR : argument count not satisfied!\n");
exit(1);
}
/* It is important to check all system calls (open, creat, dup, etc.) for a return value < 0,
particularly -1 because such a return value means an error has occurred. */
int fd_in = open(argv[1], O_RDONLY);
if (fd_in < 0)
{
fprintf(stderr,"%s", "ERROR : file to be read does not exist!\n");
exit(1);
}
int fd_out = creat(argv[2], 0644); /* mode = permissions, here rw-r--r-- */
if (fd_out < 0)
{
fprintf(stderr,"%s", "ERROR : file could not be created!\n");
exit(1);
}
if(dup(fd_in) < 0)//dup fd_in to 3
fprintf(stderr , "ERROR assigning STREAM 3 to fd_in");
if(dup(fd_out) < 0)//dup fd_in to 4
fprintf(stderr , "ERROR assigning STREAM 4 to fd_out");
//dup fd_in to 0
close(0);
dup(fd_in);
close(3);
//dup fd_out to 1
close(1);
dup(fd_out);
close(4);
int fd[2];
pipe(fd);
pid_t pid_child_1, pid_child_2;
int status;
if ((pid_child_1 = fork()) != 0)
{
if ((pid_child_2 = fork()) != 0)
{
close(fd[0]);
close(fd[1]);
wait(&status);
wait(&status);
// fprintf(stderr , "\nstatus of child_1 = %d",wait(&status));
// fprintf(stderr , "\nstatus of child_2 = %d",wait(&status));
}
else
{
// close(fd[1]);
// dup(1);
dup2(fd[1],1);
close(fd[0]);
execl( CONVERT_PROGRAM, CONVERT_PROGRAM, (char*) NULL);
}
}
else
{
// close(fd[0]);
// dup(0);
dup2(fd[0],0);
close(fd[1]);
execl( COUNT_PROGRAM , COUNT_PROGRAM ,(char*) NULL);
}
}
After compiling my text file which should contain the output is empty. THOSE PROGRAMS ARE WORKING WELL ALONE.
Here I am adding the strace result after running the strace command. Here it is printing 7 on the screen and no output in the text file.
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\20\35\2\0\0\0\0\0"..., 8 32) = 832
strace: Process 6018 attached
strace: Process 6019 attached
[pid 6019] read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\20\35\2\0\0\ 0\0\0"..., 832) = 832
[pid 6018] read(4, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\20\35\2\0\0\ 0\0\0"..., 832) = 832
[pid 6019] read(0, "hello my name is himanshu KAUSHI"..., 4096) = 35
[pid 6019] read(0, "", 4096) = 0
[pid 6019] write(1, "HELLO MY NAME IS HIMANSHU kaushi"..., 35) = 35
[pid 6019] +++ exited with 0 +++
[pid 6018] read(0, "HELLO MY NAME IS HIMANSHU kaushi"..., 4096) = 35
[pid 6017] --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=6019, si_u id=1062, si_status=0, si_utime=0, si_stime=0} ---
[pid 6018] read(0, "", 4096) = 0
[pid 6018] write(2, "\n7", 2
7) = 2
[pid 6018] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=6018, si_uid=1062, si_ status=0, si_utime=0, si_stime=0} ---
+++ exited with 0 +++
I changed standard table descriptors in 1st dup2(f_dsc[1],3) command and I got the output in the text file but then my first program stooped running.
#include<stdio.h>
#include<ctype.h>
int main()
{
char c;
int count=0;
while(1)
{
c=getchar();
if(c==EOF)
{
break;
}
if(!isalpha(c))
{
count++;
}
}
fprintf(stderr,"\n%d",count);
}
this is my simple b program.
#include<stdio.h>
#include<ctype.h>
int main()
{
char c;
int count=0;
while(1)
{
c=getchar();
if(c==EOF)
{
break;
}
if(islower(c))
{
c=toupper(c);
}
else
{
c=tolower(c);
}
putchar(c);
}
return 0;
}
and this is my simple c program.
