C in linux/unix

[adi007]

^^hmmm no responses

When a value greater than the size is stored in a variable, the value is wrapped around from the lower end. ie if the maximum value is 32767, and you try to store 32768, it'll wrap-around to -32768

How C compiler decides Garbage value in case of dataoverflow
FInd this out in my lesser known facts in c thread.
*www.thinkdigit.com/forum/showthread.php?p=655539#post655539

 

[adi007]

No contributions and responses .Looks like no one has liked this thread.

Compilation or linking of mutiple files to a single file

Another advantage of running c in linux is compliation or linking of multiple c files into a single file.Here multiple files means not multiple programs but the files which contains the part or functions of the main program.

consider the following C program

#include<stdio.h>
int main()
{
void func1(void);
void func2(void);
printf("Main function start\n");
func1();
func2();
printf("Main function end\n");
}

void func1()
{
printf("First function\n");
}

void func2()
{
printf("Second function\n");
}

When you run this program, the output will be

Main function start
First function
Second function
Main function end

With linux, there is no restriction that the functions func1 and func2 must be written in the same file itself.
i.e,.
save this as func.c

#include<stdio.h>
int main()
{
void func1(void);
void func2(void);
printf("Main function start\n");
func1();
func2();
printf("Main function end\n");
}

this as func1.c

void func1()
{
printf("First function\n");
}

and finally this as func2.c

void func2()
{
printf("Second function\n");
}

Now as u can see the above program is split into 3 parts.one the main program and the remaining 2 functions.
now in order to compile the above 3 programs as a single file you have to issue command

bash-2.05b$ cc -o output.out func.c func1.c func2.c

In general the syntax is

cc -o <outputfilename>  <input files>

Also, if you want to give your executable file a different name than a.out, use

cc -o <output file> <source file>

The 3 files will be compiled as one.Now to run the program type ./output.out.The same output you will get as given above

You can divide the main program only at the points of the end of the function.That means u cannot split the program as

#include<stdio.h>
int main()
{
void func1(void);
void func2(void);
printf("Main function start\n");
func1();
func2();

and

printf("Main function ends\n");
}

Some of the uses of linking are:

1.Improves redability of the main program
2.file containing the function can be used by other programs.That means once you create a separate file for a function,u can reuse it if other program requires the function.all you have do it is specify the function declaration in the main program and link this function during compilation.
3.makes the main program look small and hence debugging is easy.

 

[praka123]

isnt cc symlinked to gcc.cc is for original unix systems may be.

 

[QwertyManiac]

praka123 - Yes it is, but why the doubt?

 

[mehulved]

isnt cc symlinked to gcc.cc is for original unix systems may be.

I would avoid such assumptions after the dash fiasco

 

[QwertyManiac]

How would dash be related to a symlink? I don't understand, do explain if you get the time.

Also, why does cat /usr/bin/cc makes one's terminal go fscky?

 

[mehulved]

How would dash be related to a symlink? I don't understand, do explain if you get the time.

dash won't but what if cc was linked to another compiler and not gcc. You can't guarantee your program to build then. It may just work fine or maybe not at all.

Also, why does cat /usr/bin/cc makes one's terminal go fscky?

using cat on any binary would do that.

 

[QwertyManiac]

Well, man cc gives a gcc document page, same as what man gcc gives. So its symlinked

 

[praka123]

^in BSD's they may not be using gcc.hence cc

 

[Sykora]

@qwerty : Not exactly...

$> which cc
/usr/lib/ccache/cc
$> ls /usr/lib/ccache/cc
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 /usr/lib/ccache/cc -> /usr/bin/ccache
$> ls /usr/lib/ccache
total 0
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 c++ -> /usr/bin/ccache
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 cc -> /usr/bin/ccache
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 g++ -> /usr/bin/ccache
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 gcc -> /usr/bin/ccache
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 i386-redhat-linux-c++ -> /usr/bin/ccache
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 i386-redhat-linux-g++ -> /usr/bin/ccache
lrwxrwxrwx 1 root root 15 2007-10-31 21:12 i386-redhat-linux-gcc -> /usr/bin/ccache
$>