Where can I legally declare a variable in C99?

Question

When I was first introduced to C I was told to always declare my variables at the top of the function. Now that I have a strong grasp of the language I am focusing my effor

Answer 1

In C99, you can declare your variables where you need them, just like C++ allows you to do that.

void somefunc(char *arg)
{
    char *ptr = "xyz";
    if (strcmp(arg, ptr) == 0)
    {
        int abc = 0;    /* Always could declare variables at a block start */

        somefunc(arg, &ptr, &abc);

        int def = another_func(abc, arg);   /* New in C99 */
        ...other code using def, presumably...
    }
}

• You can declare a variable in the control part of a 'for' loop:

    for (int x = 0; x < 10; x++)    /* New in C99 */
  

• You cannot declare a variable in the control part of a 'while' loop or an 'if' statement.

• You cannot declare a variable in a function call.

• Obviously, you can (and always could) declare variables in the block after any loop or an 'if' statement.

The C99 standard says:

6.8.5.3 The for statement

The statement

for ( clause-1 ; expression-2 ; expression-3 ) statement

behaves as follows: The expression expression-2 is the controlling expression that is evaluated before each execution of the loop body. The expression expression-3 is evaluated as a void expression after each execution of the loop body. If clause-1 is a declaration, the scope of any variables it declares is the remainder of the declaration and the entire loop, including the other two expressions; it is reached in the order of execution before the first evaluation of the controlling expression. If clause-1 is an expression, it is evaluated as a void expression before the first evaluation of the controlling expression.