Why is the asterisk before the variable name, rather than after the type?

Question

Why do most C programmers name variables like this:

int *myVariable;

rather than like this:

int* myVariable;

Answer 1

They are EXACTLY equivalent. However, in

int *myVariable, myVariable2;

It seems obvious that myVariable has type int*, while myVariable2 has type int. In

int* myVariable, myVariable2;

it may seem obvious that both are of type int*, but that is not correct as myVariable2 has type int.

Therefore, the first programming style is more intuitive.

Answer 2

A lot of the arguments in this topic are plain subjective and the argument about "the star binds to the variable name" is naive. Here's a few arguments that aren't just opinions:

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The forgotten pointer type qualifiers

Formally, the "star" neither belongs to the type nor to the variable name, it is part of its own grammatical item named pointer. The formal C syntax (ISO 9899:2018) is:

(6.7) declaration:
declaration-specifiers init-declarator-list_opt ;

Where declaration-specifiers contains the type (and storage), and the init-declarator-list contains the pointer and the variable name. Which we see if we dissect this declarator list syntax further:

(6.7.6) declarator:
pointer_opt direct-declarator
...
(6.7.6) pointer:
* type-qualifier-list_opt
* type-qualifier-list_opt pointer

Where a declarator is the whole declaration, a direct-declarator is the identifier (variable name), and a pointer is the star followed by an optional type qualifier list belonging to the pointer itself.

What makes the various style arguments about "the star belongs to the variable" inconsistent, is that they have forgotten about these pointer type qualifiers. int* const x, int *const x or int*const x?

Consider int *const a, b;, what are the types of a and b? Not so obvious that "the star belongs to the variable" any longer. Rather, one would start to ponder where the const belongs to.

You can definitely make a sound argument that the star belongs to the pointer type qualifier, but not much beyond that.

The type qualifier list for the pointer can cause problems for those using the int *a style. Those who use pointers inside a typedef (which we shouldn't, very bad practice!) and think "the star belongs to the variable name" tend to write this very subtle bug:

    /*** bad code, don't do this ***/
    typedef int *bad_idea_t; 
    ...
    void func (const bad_idea_t *foo);

This compiles cleanly. Now you might think the code is made const correct. Not so! This code is accidentally a faked const correctness.

The type of foo is actually int*const* - the outer most pointer was made read-only, not the pointed at data. So inside this function we can do **foo = n; and it will change the variable value in the caller.

This is because in the expression const bad_idea_t *foo, the * does not belong to the variable name here! In pseudo code, this parameter declaration is to be read as const (bad_idea_t *) foo and not as (const bad_idea_t) *foo. The star belongs to the hidden pointer type in this case - the type is a pointer and a const-qualified pointer is written as *const.

But then the root of the problem in the above example is the practice of hiding pointers behind a typedef and not the * style.

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Regarding declaration of multiple variables on a single line

Declaring multiple variables on a single line is widely recognized as bad practice¹⁾. CERT-C sums it up nicely as:

DCL04-C. Do not declare more than one variable per declaration

Just reading the English, then common sense agrees that a declaration should be one declaration.

And it doesn't matter if the variables are pointers or not. Declaring each variable on a single line makes the code clearer in almost every case.

So the argument about the programmer getting confused over int* a, b is bad. The root of the problem is the use of multiple declarators, not the placement of the *. Regardless of style, you should be writing this instead:

    int* a; // or int *a
    int b;

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Another sound but subjective argument would be that given int* a the type of a is without question int* and so the star belongs with the type qualifier.

But basically my conclusion is that many of the arguments posted here are just subjective and naive. You can't really make a valid argument for either style - it is truly a matter of subjective personal preference.

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1) CERT-C DCL04-C.

Answer 3

People who prefer int* x; are trying to force their code into a fictional world where the type is on the left and the identifier (name) is on the right.

I say "fictional" because:

In C and C++, in the general case, the declared identifier is surrounded by the type information.

That may sound crazy, but you know it to be true. Here are some examples:

• int main(int argc, char *argv[]) means "main is a function that takes an int and an array of pointers to char and returns an int." In other words, most of the type information is on the right. Some people think function declarations don't count because they're somehow "special." OK, let's try a variable.

• void (*fn)(int) means fn is a pointer to a function that takes an int and returns nothing.

• int a[10] declares 'a' as an array of 10 ints.

• pixel bitmap[height][width].

• Clearly, I've cherry-picked examples that have a lot of type info on the right to make my point. There are lots of declarations where most--if not all--of the type is on the left, like struct { int x; int y; } center.

This declaration syntax grew out of K&R's desire to have declarations reflect the usage. Reading simple declarations is intuitive, and reading more complex ones can be mastered by learning the right-left-right rule (sometimes call the spiral rule or just the right-left rule).

C is simple enough that many C programmers embrace this style and write simple declarations as int *p.

In C++, the syntax got a little more complex (with classes, references, templates, enum classes), and, as a reaction to that complexity, you'll see more effort into separating the type from the identifier in many declarations. In other words, you might see see more of int* p-style declarations if you check out a large swath of C++ code.

In either language, you can always have the type on the left side of variable declarations by (1) never declaring multiple variables in the same statement, and (2) making use of typedefs (or alias declarations, which, ironically, put the alias identifiers to the left of types). For example:

typedef int array_of_10_ints[10];
array_of_10_ints a;

Answer 4

Something nobody has mentioned here so far is that this asterisk is actually the "dereference operator" in C.

*a = 10;

The line above doesn't mean I want to assign 10 to a, it means I want to assign 10 to whatever memory location a points to. And I have never seen anyone writing

* a = 10;

have you? So the dereference operator is pretty much always written without a space. This is probably to distinguish it from a multiplication broken across multiple lines:

x = a * b * c * d
  * e * f * g;

Here *e would be misleading, wouldn't it?

Okay, now what does the following line actually mean:

int *a;

Most people would say:

It means that a is a pointer to an int value.

This is technically correct, most people like to see/read it that way and that is the way how modern C standards would define it (note that language C itself predates all the ANSI and ISO standards). But it's not the only way to look at it. You can also read this line as follows:

The dereferenced value of a is of type int.

So in fact the asterisk in this declaration can also be seen as a dereference operator, which also explains its placement. And that a is a pointer is not really declared at all, it's implicit by the fact, that the only thing you can actually dereference is a pointer.

The C standard only defines two meanings to the * operator:

• indirection operator
• multiplication operator

And indirection is just a single meaning, there is no extra meaning for declaring a pointer, there is just indirection, which is what the dereference operation does, it performs an indirect access, so also within a statement like int *a; this is an indirect access (* means indirect access) and thus the second statement above is much closer to the standard than the first one is.

Answer 5

I'm going to go out on a limb here and say that there is a straight answer to this question, both for variable declarations and for parameter and return types, which is that the asterisk should go next to the name: int *myVariable;. To appreciate why, look at how you declare other types of symbol in C:

int my_function(int arg); for a function;

float my_array[3] for an array.

The general pattern, referred to as declaration follows use, is that the type of a symbol is split up into the part before the name, and the parts around the name, and these parts around the name mimic the syntax you would use to get a value of the type on the left:

int a_return_value = my_function(729);

float an_element = my_array[2];

and: int copy_of_value = *myVariable;.

C++ throws a spanner in the works with references, because the syntax at the point where you use references is identical to that of value types, so you could argue that C++ takes a different approach to C. On the other hand, C++ retains the same behaviour of C in the case of pointers, so references really stand as the odd one out in this respect.

Answer 6

Consider

int *x = new int();

This does not translate to

int *x;
*x = new int();

It actually translates to

int *x;
x = new int();

This makes the int *x notation somewhat inconsistent.