CODEWITHSUNDEEP
cswitch-statementdeclaration
Sheldor
Sheldor

Reputation: 1

Declaring same variable within a case label in switch statement

I'm wondering if we can declare something like below. My requirement was to use same variable but different structures. Can you guys help me if the below can be done? Please suggest if there are other options as well.

switch(x)
{
  case 1:
    struct_1 *name = NULL;
    break;
  case 2:
    struct_2 *name = NULL;
    break;
  case 3:
    struct_3 *name = NULL;
    break;
  default:
}

Regards

Upvotes: 0

Views: 762

Answers (5)

K.Isbruch
K.Isbruch

Reputation: 175

void pointers can be dereferenced, otherwise they would be mostly useless. But the compiler needs to know what data type the pointer is pointing to, so you have to use a typecast whenever you want to acces the data the pointer is pointing to.

miikkas answer above already shows an example of how the typecast looks like.

Upvotes: 0

miikkas
miikkas

Reputation: 818

Union

To be able to use the same variable name for different types, you could also use a union of the different types and declare the variable of that union type before the switch statement.

Example code:

typedef union {
    struct_1 s1;
    struct_2 s2;
    struct_3 s3;
} anyof123;

and before the switch statement:

anyof123 *name = malloc(sizeof(anyof123)); // Example, allocate some memory.

and in the switch statement:

case 1:
    {
        struct_1 s1 = ...; // Just an example, fill with your own declaration.
        name->s1 = s1;
    }
    break;

and the resulting variable name can be accessed outside the switch scope afterwards.

Void pointer

As pointed out by Kavan Shah, you could use a void pointer and remember to cast it to the wanted type each time you access it, like this:

((struct_1*)name)->my_data = ...;

Upvotes: 0

Kavan Shah
Kavan Shah

Reputation: 11

If I understand that you want to keep same variable "name" and use it later on as pointer to structure selected by case. Then you can use void *name (declare before switch), and in each case type-cast this pointer as per the desired structure pointer. And use "name" later on as and when required.

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409196

Case labels don't introduce a new scope. You either have to declare them before the switch with different names, or enclose the code in each case in braces like

case 1:
    {
        struct_1 *name = NULL;
        ...
    }
    break;
case 2:
    {
        struct_2 *name = NULL;
        ...
    }
    break;

Upvotes: 5

Shumail
Shumail

Reputation: 3143

Declare variables before switch

Upvotes: 0

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