Two C question: definition of veriable and

powerplane · 04-30-2003, 05:08 AM

Question 1.
To my very limited knowledge of C lang, in a func, the veriable must definition before any operation, right?
that is to say, this code is wrong:

Quote:

#include <stdio.h>

int
main ( int argc, char* argv[ ] )
{
int a = 1;
int b = 2;

a = a + b;

int c;

printf ("Hello,world!\n") ;
return 0;

}

Can some compile flag make gcc compile this code successfully, and the bin can be runned flawless?

Question 2.
Why make function static?
Such as:

Quote:

static void foo(void);

yrraja · 04-30-2003, 07:56 AM

Q1) I dont think there is a gcc flag to avoid this error. There is one way though, i dont know if it would suit you. You simply change the the extention of your '.c' files to '.cpp' and use gcc to compile it. Then you wont get errors for those declarations because the compiler will treat them as c++ files.

Q2) If you declare a function 'static' then the scope of this function will set to this file only. Only other functions in the same file will be able to call it. You will not be able to call this function from other files by declaring its prototype in header files etc.

Yaser

powerplane · 04-30-2003, 08:09 AM

Thanks,yrraja. I finally figure out.
I did some experiment, and here is my found:
I will give some example to illustrate.

Allowed

Quote:

Code:

int
foo_a(void)
{
      int a =100;
      a++;
      {
           int b;
      }

}

int
foo_b(void)
{
     int a=100;
     int b=200;
      a++;
     {
          int b=50;
          printf("%d, %d\n", a, b); /*print outside a,100 and "inner" b, 50*/
     }
     printf("%d\n",b);  /*print, "outside" b,200 */
}

Not Allowed

Code:

int
bar_a(void)
{
      int a =100;
      a++;
      int b;
}

int
bar_b(void)
{ 
     int a;
     {
          a++;
           int b; /*operation before definition*/
     }
}
int
bar_c(void)
{
      {
      int a = 100;
      }
      print(a);   /*wrong, the outside a is not declared */
}

That means definite a variable in a "if() { }", "for() {} ", "while() {}",etc, is allowed, but must put at the very beginning in the scope of "{}", before any operation.

llama_meme · 05-01-2003, 05:07 AM

Strictly speaking, the latest ANSI C standard does allow variables to be declared in the middle of a function (and local to for loops, etc.), but gcc 2.x doesn't implement this standard, so it's not a good idea to take advantage of it yet.

Alex

yrraja · 05-01-2003, 10:59 PM

Yes powerplane your experiments are absolutely correct. You can declare variables at the begining of a scope. But only thing that you need to keep into consideration is that you cannot use this variable after the closing bracket of this scope.

Yaser