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Q&A Are there references in C?

Yes there are references and pass-by-reference in C, though the language has no explicit syntax item called "reference" like C++. In a C context, it is irrelevant that C++ happens to have something...

posted 3y ago by Lundin‭ · edited 3y ago by Lundin‭

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#3: Post edited by

Lundin‭ · 2022-01-27T14:47:55Z (almost 3 years ago)

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Yes there are references and pass-by-reference in C, though the language has no explicit syntax item called "reference" like C++. In a C context, it is irrelevant that C++ happens to have something called references, which are basically glorified, read-only pointers.
The general computer science term [reference](https://en.wikipedia.org/wiki/Reference_(computer_science)) pre-dates C and C++ both. As explained in that wikipedia link, it is analogous to indirect access, which is a term used in assembler on the low-level machine code layer. There, direct addressing means accessing a value directly from a given address, but indirect addressing means accessing it through a provided index register containing the address. These CPU core index registers are where C and C++ compilers prefer to store the higher level concepts of pointers and references. But there is no distinction between pointers and references in the machine code - it's all translated to raw addresses.
Therefore, saying "pass by reference" is perfectly acceptable in any computer science context. It is a broad and general term.
---
If we look at the formal definitions of terms in the current ISO 9899:2018 C standard, we find this at 6.2.5/20:
> A _pointer type_ may be derived from a function type or an object type, called the _referenced type_. A pointer type describes an object whose value provides a reference to an entity of the referenced
type. A pointer type derived from the referenced type "_T_" is sometimes called “pointer to _T_”.
A pointer type is a so-called _derived type_, meaning that it is always based on one of the object types (like `int`).
---
Given these formal definitions, then we can look at the code example in the question:
`void func (int* x);`
- The pointer type is `int*`, here represented by the variable `x`, and it is passed by value.
- The referenced type is `int` and an object of that type, allocated elsewhere, is passed by reference.
`int* p = &data;`
- `p` is a pointer type.
- `data` is a complete object type, presumably of type `int`.
`func(p);`
- `p` is passed by value.
- `data` is passed by reference.

Yes there are references and pass-by-reference in C, though the language has no explicit syntax item called "reference" like C++. In a C context, it is irrelevant that C++ happens to have something called references, which are basically glorified, read-only pointers.
The general computer science term [reference](https://en.wikipedia.org/wiki/Reference_(computer_science)) pre-dates C and C++ both. Therefore, saying "pass by reference" is perfectly acceptable in any computer science context. It is a broad and general term.
As explained in that Wikipedia link, it is analogous to indirect access, which is a term used in assembler on the low-level machine code layer. There, direct addressing means accessing a value directly from a given address, but indirect addressing means accessing it through a provided index register containing the address. These CPU core index registers are where C and C++ compilers prefer to store the higher level concepts of pointers and references. But there is no distinction between pointers and references in the machine code - it's all translated to raw addresses.
---
If we look at the formal definitions of terms in the current ISO 9899:2018 C standard, we find this at 6.2.5/20:
> A _pointer type_ may be derived from a function type or an object type, called the _referenced type_. A pointer type describes an object whose value provides a reference to an entity of the referenced
type. A pointer type derived from the referenced type "_T_" is sometimes called “pointer to _T_”.
A pointer type is a so-called _derived type_, meaning that it is always based on one of the object types (like `int`).
---
Given these formal definitions, then we can look at the code example in the question:
`void func (int* x);`
- The pointer type is `int*`, here represented by the variable `x`, and it is passed by value.
- The referenced type is `int` and an object of that type, allocated elsewhere, is passed by reference.
`int* p = &data;`
- `p` is a pointer type.
- `data` is a complete object type, presumably of type `int`.
`func(p);`
- `p` is passed by value.
- `data` is passed by reference.

#2: Post edited by

Lundin‭ · 2022-01-27T14:38:36Z (almost 3 years ago)

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Yes there are references and pass-by-references in C, though the language has no explicit syntax item called "reference" like C++. In a C context, it is irrelevant that C++ happens to have something called references, which are basically glorified, read-only pointers.
The general computer science term [reference](https://en.wikipedia.org/wiki/Reference_(computer_science)) pre-dates C and C++ both. As explained in that wikipedia link, it is analogous to indirect access, which is a term used in assembler on the low-level machine code layer. There, direct addressing means accessing a value directly from a given address, but indirect addressing means accessing it through a provided index register containing the address. These CPU core index registers are where C and C++ compilers prefer to store the higher level concepts of pointers and references. But there is no distinction between pointers and references in the machine code - it's all translated to raw addresses.
Therefore, saying "pass by reference" is perfectly acceptable in any computer science context. It is a broad and general term.
---
If we look at the formal definitions of terms in the current ISO 9899:2018 C standard, we find this at 6.2.5/20:
> A _pointer type_ may be derived from a function type or an object type, called the _referenced type_. A pointer type describes an object whose value provides a reference to an entity of the referenced
type. A pointer type derived from the referenced type "_T_" is sometimes called “pointer to _T_”.
A pointer type is a so-called _derived type_, meaning that it is always based on one of the object types (like `int`).
---
Given these formal definitions, then we can look at the code example in the question:
`void func (int* x);`
- The pointer type is `int*`, here represented by the variable `x`, and it is passed by value.
- The referenced type is `int` and an object of that type, allocated elsewhere, is passed by reference.
`int* p = &data;`
- `p` is a pointer type.
- `data` is a complete object type, presumably of type `int`.
`func(p);`
- `p` is passed by value.
- `data` is passed by reference.

Yes there are references and pass-by-reference in C, though the language has no explicit syntax item called "reference" like C++. In a C context, it is irrelevant that C++ happens to have something called references, which are basically glorified, read-only pointers.
The general computer science term [reference](https://en.wikipedia.org/wiki/Reference_(computer_science)) pre-dates C and C++ both. As explained in that wikipedia link, it is analogous to indirect access, which is a term used in assembler on the low-level machine code layer. There, direct addressing means accessing a value directly from a given address, but indirect addressing means accessing it through a provided index register containing the address. These CPU core index registers are where C and C++ compilers prefer to store the higher level concepts of pointers and references. But there is no distinction between pointers and references in the machine code - it's all translated to raw addresses.
Therefore, saying "pass by reference" is perfectly acceptable in any computer science context. It is a broad and general term.
---
If we look at the formal definitions of terms in the current ISO 9899:2018 C standard, we find this at 6.2.5/20:
> A _pointer type_ may be derived from a function type or an object type, called the _referenced type_. A pointer type describes an object whose value provides a reference to an entity of the referenced
type. A pointer type derived from the referenced type "_T_" is sometimes called “pointer to _T_”.
A pointer type is a so-called _derived type_, meaning that it is always based on one of the object types (like `int`).
---
Given these formal definitions, then we can look at the code example in the question:
`void func (int* x);`
- The pointer type is `int*`, here represented by the variable `x`, and it is passed by value.
- The referenced type is `int` and an object of that type, allocated elsewhere, is passed by reference.
`int* p = &data;`
- `p` is a pointer type.
- `data` is a complete object type, presumably of type `int`.
`func(p);`
- `p` is passed by value.
- `data` is passed by reference.

#1: Initial revision by

Lundin‭ · 2022-01-27T14:37:57Z (almost 3 years ago)

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Yes there are references and pass-by-references in C, though the language has no explicit syntax item called "reference" like C++. In a C context, it is irrelevant that C++ happens to have something called references, which are basically glorified, read-only pointers.

The general computer science term [reference](https://en.wikipedia.org/wiki/Reference_(computer_science)) pre-dates C and C++ both. As explained in that wikipedia link, it is analogous to indirect access, which is a term used in assembler on the low-level machine code layer. There, direct addressing means accessing a value directly from a given address, but indirect addressing means accessing it through a provided index register containing the address. These CPU core index registers are where C and C++ compilers prefer to store the higher level concepts of pointers and references. But there is no distinction between pointers and references in the machine code - it's all translated to raw addresses.

Therefore, saying "pass by reference" is perfectly acceptable in any computer science context. It is a broad and general term.

---

If we look at the formal definitions of terms in the current ISO 9899:2018 C standard, we find this at 6.2.5/20:

> A _pointer type_ may be derived from a function type or an object type, called the _referenced type_. A pointer type describes an object whose value provides a reference to an entity of the referenced
type. A pointer type derived from the referenced type "_T_" is sometimes called “pointer to _T_”.

A pointer type is a so-called _derived type_, meaning that it is always based on one of the object types (like `int`).

---

Given these formal definitions, then we can look at the code example in the question:

`void func (int* x);`
- The pointer type is `int*`, here represented by the variable `x`, and it is passed by value.
- The referenced type is `int` and an object of that type, allocated elsewhere, is passed by reference.

`int* p = &data;`
- `p` is a pointer type.
- `data` is a complete object type, presumably of type `int`.

`func(p);`
- `p` is passed by value.
- `data` is passed by reference.

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