Maybe there's more than 512 bytes of output, and you're forcing it to close before it's finished? This will break the pipe, causing it to get the signal SIGPIPE which will kill it prematurely, which will give you a weird exit code.
You can also use the fread command since you've converted it to a FILE * anyway.
ok i changed it to fread and fwrite and it works now.
also if i change a value of a file pointer array to 0, and then if it gets compared to a NULL value will it crash? or should i just change it to a NULL value.
also when testing when i changed all the fread/fwrite amount to 1000 for maximum bytes used, i get errors like
/bin/sh: hdü·ls: not found
but if i keep it to like 512 it works fine, why is this?
also can you explain again why the command "ls; ls" prints the files line by line for each filename and not all in a line?
if i do fwrite, i get the output like
___ ___ ___ ___
___ ___ ___ ___
but otherwise when the execl command runs the output is like
___
___
___
___
___
etc
also if i change a value of a file pointer array to 0, and then if it gets compared to a NULL value will it crash?
I repeat: Setting an array element doesn't cause a program to crash. (Unless you went past the end of the array). Invalid pointers can't do anything -- they just sit there. Even intentionally setting an invalid pointer won't cause a program to crash right then and there.
Your program crashes when it tries to dereference an invalid pointer.
In short:
Quote:
also when testing when i changed all the fread/fwrite amount to 1000 for maximum bytes used, i get errors like
/bin/sh: hdü·ls: not found
but if i keep it to like 512 it works fine, why is this?
Post your complete code. I can't tell why from here but it sounds like you forgot to check how many bytes you actually read again. You can't assume you got 1000, you could easily have gotten less!
Furthermore, don't write 1000 bytes unless you actually have 1000 bytes to write. Only write the number of bytes you actually have...
Quote:
also can you explain again why the command "ls; ls" prints the files line by line for each filename and not all in a line?
There is a system call isatty() which you can use to check if an open file descriptor is a terminal or not.
When standard output is a terminal, ls checks to see how wide your terminal is and splits up its columns accordingly.
When standard output is not a terminal it knows nothing about your screen and just prints one column.
Try ls | cat, it will print one column for exactly the same reason.
Quote:
if i do fwrite, i get the output like
___ ___ ___ ___
___ ___ ___ ___
This is because you're letting ls print directly to the screen. It will know that standard output is a terminal by checking isatty(), and check how wide your screen is, and print columns accordingly.
For the fourth time, stop using printf for this! It doesn't do what you think it does!
Quote:
also how do i use isatty() for the execl command to print it horizontally and not vertically?
You don't. You can only control whether ls gets a tty by actually giving it a tty. On some systems though, you can force ls to print columns with the -C option. I don't know if this will work for you though, since I still don't know what your system is after weeks of asking.
Last edited by Corona688; 03-16-2011 at 02:51 PM..
Hello all,
I am reading a huge zip file in POPEN process and then writting that to a normal file which of 2GB. Now the process is failing when I looked for the cause someother process comming in after I read my file and it is deleting the zip. But in theory the popen command should read the... (5 Replies)
in man system it talks about SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored.
Does this signal stuff also happen in popen command?
(even though man popen says nothing about signals)
also if I am not using wait(&status) and I am using waitpid(pid, NULL, 0)
how would... (1 Reply)
hi,
i am trying to use popen to run a grep process and check if the pattern exists in the file that i am searching in. i am getting segmentation fault when i try to execute the following code
char *cd;
char flag;
char hdr_flpsp;
char hdr_flpsp2;
FILE *fp;
printf ("program starts");... (1 Reply)
Hi
I am trying to use popen function with wrtie option to give inputs to ftp command.
#include "stdio.h"
int main(int argv ,char *argc)
{
int size=0;
char *buf;
FILE *fp;
fp = popen("ftp","w");
while(getline(&buf,&size,stdin) != -1)
write(fp,buf);... (0 Replies)
Hi!
I'm trying to write a c program. The child process must transmit to the parent a file name and the parent must count the lines from the file and return te result to the child. Here is what i've done. It doesn't stop running, I guess. I'm sorry if it's an ugly code, i'm new at this stuff,... (2 Replies)
Hello I'm writing a web server in python(obelisk-http.sourceforge.net)
and I'm having a greeat problem with POST method it like that
When someone make a POST request to the server it must open the executable(perl/python/.exe/elf) and send to the STANDART in (stdin) the request and get the... (2 Replies)
hi,
how to work with a background process without a controlling terminal to make use of popen or system call ?
when ever i use popen or system function call in foreground process, there is no problem with respect to that .. but when the same program is run as a background process without a... (7 Replies)
Hi there,
I'm facing a problem running the tar command with the popen function.
FILE* fp = popen("tar czf - textfile","r")
// output
this program should give the output to the stdout. I don't know if it is possible and which function like fprint() etc. should I use.
I suppose that I... (4 Replies)
hai friends
I have written a tcp chat server in c.. I have designed a cgi program in c to control it... When i try to start the server from the cgi program, it is not starting. Why is that ? I have even tried giving the root ownership for all the programs.. Still its not.
I have used the... (1 Reply)
Hi
The following is my program to test popen()
routine. The purpose is to print some contents
of the corrent directory.
But in fact, the output is only one character
'a', which I believe is the first char of the file
"a.out".
So, can anybody tell me what is wrong about
this program?... (2 Replies)