Difference between char *foo vs (char *)foo in Objective-C

Question

What is the difference between

char *foo

and

(char *) foo

in Objective-C?

Here is an example for both scenarios: 1. @interface Worker: NSObject { char *foo; } 2. - initWithName:(char *)foo

Answer 1

+ (char*) foo; // "static" function returning a variable of type char*
- (char*) foo; // member function returning a variable of type char*


// ...
{
    // ...
    char* foo; // variable of type char*
    // ...
}
// ...

EDIT

- (void) whatever: (char*)foo; // member function, with 
                               // parameter foo of type char*

// ...
{
    // ...
    char* bar = (char*) foo; // casting variable foo to type char* 
    // ...
}
// ...

Answer 2

There are two places your first expression can appear. The first is as a variable definition. By itself, char *foo is defining a variable - a pointer to char named foo. In the context of a function definition it defines the type of one of the function's parameters:

void function(char *foo)

Declares a function that takes a single char * argument and indicates that that argument will be referred to by the name foo in the context of the function.

There are also a couple of explanations for your other expression. The first is in the case of a method definition, which is similar to the function declaration above:

- (void)method:(char *)foo

Declares an instance method taking a single argument, in this case of type char * and named foo. It could also appear as the return type of the method:

- (char *)foo

Another case is as a typecast:

void *foo;
char *bar = (char *)foo;

In which case the expression typecasts foo from a void pointer to a char pointer and assigns the value to bar.

Edit:

For your particular examples:

@interface Worker: NSObject
{
    char *foo;
}

This example is declaring an instance variable named foo. It has type char *.

- initWithName:(char *)foo

This example is declaring an instance method taking one parameter named foo of type char *.