Const References in Function Arguments: `const T&` or `T const&`?

Const Reference in Function Arguments: Before or After Type-Specifier?

In C , the placement of the const reference in function arguments can raise questions. Consider the following two code snippets:

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

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

Semantically, there is no difference between these two arguments. The language treats them as the same type, both referring to a constant reference to an object of type Fred.

Stylistic Considerations:

However, when it comes to style, the preferred usage varies among programmers.

• const T&: This is the style used in Stroustrup's "The C Programming Language" and also in the C standard itself.
• T const&: This style is less commonly used but may be preferred by some for consistency with right-to-left parsing rules, considered a good practice in C .

Right-to-Left Parsing:

According to the right-to-left parsing rule, qualifiers (such as const) should be applied to the type on their left. This would support the use of T const&.

However, it's important to note that const T& can also be parsed effectively right-to-left. It indicates a reference to a constant value of type T. Furthermore, the ambiguity of T const* (which could potentially be interpreted as "pointer constant to T" instead of "pointer to constant T") makes const T& the more unambiguous choice.

Practicality:

In terms of readability and common usage, const T&/const T have gained significant momentum over T const&/T const. This may be due to the prevalence of these styles in widely recognized sources like Stroustrup's book and the C standard. Adhering to commonly accepted practices can enhance code readability.

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