calling system with linux and C

RSims

Okay i'm learning C and enjoying it pretty well, but I'm running into problems cross platform due to some slight differences. In windows I can use in a console application for example system("pause"); to pause the program until enter is pressed, etc... but that doesn't apply to Linux and the terminal window.

Is there is a list of ways to call system and what they do with C and Linux? Could use a list for Linux and Windows actually since we're on the topic. Let me know i've looked for one haven't had any luck so far though.

marc

RSims wrote:

Okay i'm learning C and enjoying it pretty well, but I'm running into problems cross platform due to some slight differences. In windows I can use in a console application for example system("pause"); to pause the program until enter is pressed, etc... but that doesn't apply to Linux and the terminal window.


Is there is a list of ways to call system and what they do with C and Linux? Could use a list for Linux and Windows actually since we're on the topic. Let me know i've looked for one haven't had any luck so far though.

You are doing it wrong (NOTE: I'm no expert)

If you are doing system calls from your program you'll get to problems because the system calls are different in every platform ( there are some standards, like POSIX which define the basic syscalls that must be present in every system...)

You'll have to know what OS standard you want to follow and then use only those system calls. That or to check which OS your app is running and then call one syscall or another depending on the platform

Regards

RSims

I figured that much out when I was trying to use system("cls"); to clear previous terminal garbage. I'm sure system calls are listed somewhere for linux and windows 7. Let me know if anyone finds them because I have had no luck looking for them.

asedt

As Marc Deop says this is the wrong way of doing things, especially if your learning C as those stuff is no part of C.

Just use getchar() instead.

http://www.gidnetwork.com/b-61.html
http://www.gidforums.com/t-12871.html

marc

RSims wrote:

I figured that much out when I was trying to use system("cls"); to clear previous terminal garbage. I'm sure system calls are listed somewhere for linux and windows 7. Let me know if anyone finds them because I have had no luck looking for them.

10secs search on google:

http://www.gnu.org/software/guile/manual/html_node/POSIX.html

Regards

RSims

um, I'm not sure if that is what I was looking for or not... but I guess I need to do more research either way... Thanks for the help.

asedt

I think we got things messed up a bit in this thread.

I don't think actual syscalls as these: http://syscalls.kernelgrok.com/ has much to do with it.

You can read more about system calls at:
http://en.wikipedia.org/wiki/System_call

This is what we talking about:

... system is a function used to execute subprocesses and commands ...

http://en.wikipedia.org/wiki/System_(C_standard_library)

So you can use it to run non C commands, witch I was trying to say earlier. And then it all depends on what system and whats installed so you don't want to use it if you can avoid it and if you need portability.

This works in Linux:

#include <stdio.h> // requred for printf.
#include <stdlib.h> // required for system.
 
// See http://en.wikipedia.org/wiki/System_%28C_standard_library%29
 
int main( int   argc, char *argv[] ){
    printf ("Text to print.");
    getchar();
    system("clear"); // clear is a terminal command in Linux. /usr/bin/clear    
    return 0;
}

Helpful list of C functions:
http://en.wikipedia.org/wiki/List_of_C_functions

chekkizhar

I don't think so, the "pause" button will work in terminal. And as Marc and Aron mentioned, there is a BIG difference when running a program in different platforms.

I don't know why you are using W******s to do 'C' progamming.

Use Linux terminal, where the C language itself developed/Enhanced.

Well, according to me,

nread=read(,,,,)

is a system call. Not,

system("clear")

Because, "system" is a library, which can be used to execute any shell commands from program,if we want. So, I won't say "system" is a system call. just my opinion Aron.
And thanks for the link Aron.

Richard, if you want Dennis Ritchie book soft copy, let me to know. I have that.

Thanks

marc

A syscall is calling something that the kernel does, isn't it?

chekkizhar

marc wrote:

A syscall is calling something that the kernel does, isn't it?

yes. To be more specific, system call is the entry ticket/point to the Kernel space from the user space. Mostly, we should avoid using system calls, unless we know , what we are doing. Always there should be a remedy option to achieve those things. Like , dmesg, passwd etc.

But, if we are doing coding work, then most of the time we need to play with system call. That will be interesting

asedt

chekkizhar wrote:

Because, "system" is a library, which can be used to execute any shell commands from program,if we want. So, I won't say "system" is a system call. just my opinion Aron.

Ok so we have the same opinion, did I miss something?

chekkizhar wrote:

Well, according to me,

nread=read(,,,,)

is a system call.

I don't agree with you on that, it's a C wrapper function to a system call.

It should be noted that the terms "system call" and "syscall" are often incorrectly used to refer to the aforementioned C standard library functions, particularly those that act as a wrapper to corresponding system calls with the same name.

http://en.wikipedia.org/wiki/System_call#The_library_as_an_intermediary

chekkizhar wrote:

And thanks for the link Aron.

Richard, if you want Dennis Ritchie book soft copy, let me to know. I have that.

Happy provider of links

I have planed to get a hard copy of K&R in a long time, I have to buy it one day.
I guess that soft copy is copyrighted right?

chekkizhar

asedt wrote:

chekkizhar wrote:

show previous quotes

Well, according to me,

nread=read(,,,,)

is a system call.

show previous quotes

I don't agree with you on that, it's a C wrapper function to a system call.

well, fread-->read-->sys_read. This is the internal flow. And upto I know, read is a system call . One more easy way to agree.

#man read

will open read man page, well second category[page]
and

#man man

will tell, second page is for system call. Easy right?

I have planed to get a hard copy of K&R in a long time, I have to buy it one day.
I guess that soft copy is copyrighted right?

I have sent one copy to your mail id. No need to waste your valuable money. If you feel anything important, you can take that page alone a print out, for example operator precedence table.

RSims

Thanks for the help Chek and everyone else.

Using windows because I needed to do system calls in my programs that I couldn't find a way to replicate in linux for my programs in my college course.

I did however use linux to program half my programs until I ran into this problem.

chekkizhar

oh. Its a college stuff then.
There must be way to do in Linux too. If you get time, you can check for that. But, sure, we can not deviate more from academic things either

RSims

I did other programs in Linux too, CodeBlocks is a great IDE. It runs on Windows, Linux and Mac/Apple OSs