Tom Lachecki

Hi. I'm here to address the age-old debate of C and C++; which pointer declaration syntax to use?

Foo<em> ptr; // (1) Foo </em> ptr; // (2) Foo *ptr; // (3)

All three are equivalent because arbitrary spacing is meaningless in C/C++.

The problem with C and C++ is that its built-in operators have multiple meanings. In particular * means "pointer type", "multiplication" and "dereference". My goal when picking a convention is to, as much as possible, avoid using one that jars with another.

Therefore, we'll ignore syntax 2 because it looks so much like multiplication.

Unfortunately, there is no clear winner between the other two as each has at least one hindrance. Syntax 1 has the following:

Foo* ptr1, ptr2;

In the code above, ptr1 is a Foo*, but ptr2 is only a Foo. One might have expected both to be Foo*s. Syntax 3 avoids this by keeping the asterisk with the name:

Foo <em>ptr1, </em>ptr2;

This is really a throwback to C's desire to have you think in terms of "I am declaring a Foo to which ptr points".

Unfortunately, this is misleading to language newcomers because in fact you're not declaring or defining a Foo at all. You're merely declaring a pointer; you still haven't allocated any actual Foo for it to point to.

A newbie reading "int *a" might think he's created an int and now gets to use "the variable *a" to access it, when in fact this is not the case at all; dereferencing such an undirected pointer would be very dangerous.

Further, aligning the asterisk with the variable name looks like a dereference operation. One of the biggest stumbling blocks to language newcomers is the multiple meaning of operators such as * and & — learning the difference between * on the LHS as a pointer type indicator and * on the RHS as a dereference operator is not aided if you see code that always aligns the asterisk in the same way.

Additionally, the name of the type itself is "Foo*" (though array declaration and function type declaration syntax oddities do make this slightly more complicated in practice).

To summarise:

In conclusion:

Foo *p is rubbish; it has three cons and two pros. Foo* p is great; it has one con and four pros… important pros.

Thanks for reading.

Updated 31/07/2010: Improved table layout for clarity.