Variable declaration after goto Label

Question

Today I found one interesting thing. I didn\'t know that one can\'t declare a variable after a goto label.

Compiling the following code

#include <         


        

Answer 1

If you know why you can't create variables inside case statement of switch, basically its the same reason why you cant do this too. As a fix, you can try this,

#include <stdio.h>
int main() {
    int x = 5;
    goto JUMP;
    printf("x is : %d\n",x);
JUMP:
    {                                              //Note this
       int a = 0;  // <=== no more error..
       printf("%d",a);
    }                                             //Note this
}

Answer 2

#include <stdio.h>
int main() {
    int x = 5;
    goto JUMP;
    printf("x is : %d\n",x);
JUMP:
    printf("Do anything after label but dont declare 
    anything. even empty statement will also work 
    because label can only be part of a statement");
    int a = 0;  
    printf("%d",a);
}

Answer 3

My gcc version (4.4) is giving this compile error:

t.c:7: error: a label can only be part of a statement and a declaration is not a statement

. This error-message says it all.

Answer 4

Well, first you should be consistent. It's either LABEL or label. Second, label is a part of the statement and the declaration doesn't answer the description enough.

You can replace LABEL: with label: ; and then it is likelier to compile.

EDIT: Now that you edited your code all over, it should be JUMP: replaced with JUMP: ; ;-)

Answer 5

The syntax simply doesn't allow it. §6.8.1 Labeled Statements:

labeled-statement:
    identifier : statement
    case constant-expression : statement
    default : statement

Note that there is no clause that allows for a "labeled declaration". It's just not part of the language.

You can trivially work around this, of course, with an empty statement.

JUMP:;
int a = 0;

Answer 6

You want a semi-colon after the label like this:

 #include <stdio.h>
 int main() {
     int x = 5;
     goto JUMP;
     printf("x is : %d\n",x);
 JUMP: ;     /// semicolon for empty statement
     int a = 0; 
     printf("%d",a);
 }    

Then your code compiles correctly for the C99 standard, with gcc -Wall -std=c99 -c krishna.c (I'm using GCC 4.6 on Debian/Sid/AMD64).