Thread: Crazy question

main is an uninitialized variable. Were you to change it to any other name, you'd still get unexpected results. (Unexpected by you, not me.) Since you haven't assigned any value to main, it contains some random value.

Quzah.

It doesn't generate a random number (as per your calling rand). We say it's random because it contains some arbitrary value of which you have not specified, and is out of your control.

Quzah.

In this case main is a global variable and would therefore(if it was legal) be initialized to zero at program startup. Your "program" appears to have "confused" the linker and your output is likely the address (or part thereof) of the main() function. In any case, don't use a global variable with the name main (or any other function name).

[edit]It is also possible that it is the value of the first byte of the main function.[/edit]

The 55H value is garbage. There's no rhyme or reason to it. If you ran the same program on a different computer or even after a reboot or running some other applications you'd probably get a different number.

When you declare a variable the compiler just sets some space aside for you to store in it. It doesn't clear that memory so whatever just happened to be in that memory location when you started the program is what's going to be printed.

Are you trying to print the address of the main() function? Try this instead:

Code:

itsme@dreams:~/C$ cat file1.c
#include <stdio.h>

extern void p2(void);

int main(void)
{
  p2();
  return 0;
}
itsme@dreams:~/C$ cat file2.c
#include <stdio.h>

extern int main(void);

void p2(void)
{
  printf("%p\n", main);
}
itsme@dreams:~/C$ gcc -Wall file1.c file2.c -o file
itsme@dreams:~/C$ ./file
0x80483f0
itsme@dreams:~/C$

Originally Posted by anonytmouse

In this case main is a global variable and would therefore(if it was legal) be initialized to zero at program startup.

You're wrong there. Only static variables are initialized (to zero). Automatic variables are not initialized.

Quzah.

Do you ever listen? It's a garbage value. It doesn't matter what it gives you, because it's your fault that it gives you some crap.

Try initializing the variable. Then what does it give you?

Code:

char main = 0;

Try changing the name of the variable, and initializing it:

Code:

char foo = 0;

There, now you've debugged your own program. Congradulations. No, wait, that was me.

Quzah.

We've told you. It gives you that value because that's whatever used that memory location last put there. It's garbage.

Look at all the garbage you can make!

Code:

itsme@dreams:~/C$ cat garbage.c
#include <stdio.h>

int main(void)
{
  unsigned char a, b, c, d, e, f;

  printf("%x %x %x %x %x %x\n", a, b, c, d, e, f);
  return 0;
}
itsme@dreams:~/C$ ./garbage
bf ff f9 58 40 0

It's amazing really.

My problem is HOW it gets 0x55.

Asked and answered.

But one more time, the answer is: "Because it feels like it."

Quzah.