Const Reference in C : Before or After the Type Specifier?

Const Reference in C : Placement Before vs. After Type Specifier

In C , when dealing with const references, there arises a question regarding the placement of the const keyword in relation to the type specifier: before or after? Let's examine the syntax and behavior of these two forms.

Syntax:

• Const Reference Before Type Specifier:

  int foo1(const Fred &arg) {
  ...
  }

• Const Reference After Type Specifier:

  int foo2(Fred const &arg) {
  ...
  }

Behavior:

Both syntaxes result in the same behavior. The language treats const T& and T const& as equivalent types. This applies to both pointer and reference declarations.

Stylistic Considerations:

While there is no functional difference between the two placement options, stylistic preferences vary. However, there are some arguments to be made for preferring const T& (and const T*):

• Consistency with Standard Texts: const T& is the style used in both the C Programming Language book by Bjarne Stroustrup and the C standard itself.
• Ubiquity: const T&/const T* is empirically more common in C and C code than its alternative placement.
• Parsing Ambiguity: Misplacing the asterisk with T const* is a potential issue, while const* T is not valid syntax.

The right-to-left parsing rule often cited in favor of placing const after the type specifier can be subjective. const T& can also be parsed right-to-left as "reference to a T constant."

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