However, because a pointer to const is not const itself (it just points to a const value), we can change what the pointer is pointing at by assigning the pointer a new address: Just like a reference to const, a pointer to const can point to non-const variables too. We can also create a constant pointer to a constant in C, which means that neither the value of the pointer nor the value of the variable pointed to by the pointer would change. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. Typically a function pointer stores the start of executable code. We can also verify that the address stored in the constant pointer remains the same after the change. The reality is even more complicated (multiple/virtual inheritance), but you get the picture For the same reason that we shall not write: outside of a class declaration. To declare a const pointer, use the const keyword after the asterisk in the pointer declaration: In the above case, ptr is a const pointer to a (non-const) int value.
* = &; * = &; qualifier from pointer target type [-Wdiscarded-qualifiers], : error: assignment of read-only variable a, // Note that it is not necessary to initialise the pointer here at the time of declaration, // This is not allowed because 'a' is const, : error: assignment of read-only location *ptr, "Address stored in pointer before change : %d\n", "Value stored in that address before change : %d\n\n", "Address stored in pointer after change : %d\n", "Value stored in that address after change : %d\n". Lastly, we try to print the value of the variable which is pointed by the pointer 'ptr'. acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Full Stack Development with React & Node JS (Live), Fundamentals of Java Collection Framework, Full Stack Development with React & Node JS(Live), GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, An Uncommon representation of array elements, Delete a Linked List node at a given position, Find Length of a Linked List (Iterative and Recursive), Search an element in a Linked List (Iterative and Recursive), Write a function to get Nth node in a Linked List, Dynamic Memory Allocation in C using malloc(), calloc(), free() and realloc(), Left Shift and Right Shift Operators in C/C++, Different Methods to Reverse a String in C++, Pointers in C and C++ | Set 1 (Introduction, Arithmetic and Array), http://www.cs.cmu.edu/~ab/15-123S11/AnnotatedNotes/Lecture14.pdf. Penrose diagram of hypothetical astrophysical white hole. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Are function pointers const? Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? If the pointer could be casted to a normal function pointer, this object would be missing and probably all parameters would be messed up as a consequence. If it is not intended for a pointer variable that is passed as a parameter to a function to change its value, then declaring the pointer as constant acts as a check against accidental modifications. const char* is, as you said, a pointer to a char, where you can't change the value of the char (at least not through the pointer (without casting the constness away)). Connect and share knowledge within a single location that is structured and easy to search. How to detect non IEEE-754 float, and how to use them? var functionName = function() {} vs function functionName() {}. Thanks for helping to make the site better for everyone! Typically a function pointer stores the start of executable code. Yes a pointer can point to any object in C. Instead pointing at variable, a function pointer points at executable code. What am I doing wrong? Constant pointer can't be declared without initialisation. The above snippet wont compile -- we cant set a normal pointer to point at a const variable. The advantage of the first method is an uncluttered syntax. You are breaking the "contract" you made by returning a constant pointer, but since C is a weakly-typed language it is syntactically legal. If the const . We have also changed function call by removing *, the program still works. Unlike the constant pointer discussed previously, a pointer to a constant in C refers to an ordinary pointer variable that can only store the address of a constant variable, i.e., a variable defined using the const keyword. This is done by placing an additional asterisk in front of its name. Thanks in advance! This is because you return a pure pointer value, that is to say a pointer value not actually stored in a pointer variable. They could have written (const uint8_t *) with the same end result. However, it makes it look as if fnptr is a function, as opposed to being a function pointer. thx for the insanely fast answsers! To create any constant pointer the first thing which we need is the data type of the pointer. In C++0x, directly calling func with the function-call syntax as a decltype operand, will yield int * const. Lastly, we print the value of the variable, which is pointed by the pointer 'ptr'. We use function pointer to call a function or to pass reference of a function to another function. In fact we can use this search function to find close elements (below a threshold) by writing a customized compare function. For the part below I use typedef double (*function)(double *x). For example a simple qsort() function can be used to sort arrays in ascending order or descending or by any other order in case of array of structures. If you do not use the const modifier with the parameter, so far as the compiler is concerned, the function may modify the data pointed to by the argument. 9. Refer this book for more details. For example, in the below program, we have removed address operator & in assignment. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Ltd. : error: assignment of read-only variable ptr, // This is allowed because only the pointer is constant and not the variable 'a'. The syntax for declaring a const pointer in C is. type * const variable = some memory address ; Const Data with a Const Pointer To combine the two modes of const-ness with pointers, you can simply include const for both data and pointer by putting const both before and after the *: const type * const variable = some memory address ; or type const * const variable = some memory address ; Similarly, constant pointer is a pointer variable whose value cannot be altered throughout the program. Function Pointers point to code like normal pointers. To make a member function constant, the keyword "const" is appended to the function prototype and also to the function definition header. Therefore, we conclude that the constant pointer to a constant can change neither address nor value, which is pointing by this pointer. With normal (non-const) pointers, we can change both what the pointer is pointing at (by assigning the pointer a new address to hold) or change the value at the address being held (by assigning a new value to the dereferenced pointer). The address of these pointers can be changed, but the value of the variable that the pointer points cannot be changed. As described earlier, a constant pointer in C is one whose value cannot be changed in the program. Read design by contract. Mail us on [emailprotected], to get more information about given services. This type of pointer is essentially a combination of the two types discussed previously, i.e., a combination of constant pointer and a pointer to a constant. Then, we assign the address of variable 'b' to the pointer 'ptr'. The following code throws an error when we try to change the value of the pointer or the value of the constant variable using the pointer. The const modifier implies that the function will not change the data that are pointed to, so the compiler knows that an argument that is a pointer to constant data will be safe. Here's a code snippet: When compiling I get the following error: note: no known conversion for argument 1 from double To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Which means you can pass a function to another function (using . Now as ptr_ref is a reference to pointer ptr, ptr now points to j. A constant pointer to a constant is a pointer, which is a combination of the above two pointers. This indicates that the value can be changed. So a. Using generic std::function objects with member functions in one class, Examples of frauds discovered because someone tried to mimic a random sequence. Runtime and Compile-time constants in C++. Therefore, we can say that the constant pointer, which points to some variable, cannot point to another variable. You appear to have several. Declaration function_return_type (*Pointer_name) (function argument list) Example Live Demo We declare two variables, i.e., 'a' and 'b' with the values 10 and 90, respectively. Meaning of 'const' last in a function declaration of a class? Allowing the programmer to set a non-const pointer to a const value would allow the programmer to dereference the pointer and change the value. Therefore, we can say that if a constant pointer is pointing to some variable, then it cannot point to any other variable. This point in particular is very useful in C. In C, we can use function pointers to avoid code redundancy. 2) Unlike normal pointers, we do not allocate de-allocate memory using function pointers. 1) Unlike normal pointers, a function pointer points to code, not data. Function pointers are not the same as member function pointers. You need to sign in, in the beginning, to track your progress and get your certificate. Constant pointers: In constant pointers, the pointer points to a fixed memory location, and the value at that location can be changed because it is a variable, . Not only this, with function pointers and void pointers, it is possible to use qsort for any data type. How do I tell if this single climbing rope is still safe for use? A function can also be passed as an arguments and can be returned from a function. Is Energy "equal" to the curvature of Space-Time? Exactly what callback_func does depends on the button; this is why allowing . A pointer to constant is a pointer through which the value of the variable that the pointer points cannot be changed. Now each daughter class can implement multiple and different versions of functions of this type. Basically GCC is helping you here. What does the exclamation mark do before the function? As described in this article, it is not advisable to use an ordinary pointer with a. This happens because when an ordinary pointer like ptr points to a const variable, the compiler discards the constant attribute given to the variable temporarily whenever the pointer tries to modify the value of that variable. I'm confused. Declaration of a pointer to constant is given below: The above code runs successfully, and it shows the value of 'ptr' in the output. The second important attribute of any constant pointer is the keyword const. char and uint8_t are usually incompatible types; a cast is necessary to do pointer-based aliasing like this. This article is contributed by Abhay Rathi. Solution 3. Related Article:Pointers in C and C++ | Set 1 (Introduction, Arithmetic and Array), References:http://www.cs.cmu.edu/~ab/15-123S11/AnnotatedNotes/Lecture14.pdf, http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-087-practical-programming-in-c-january-iap-2010/lecture-notes/MIT6_087IAP10_lec08.pdf, http://www.cs.cmu.edu/~guna/15-123S11/Lectures/Lecture14.pdf. It is quite similar to a constant variable in C. The only difference here is that, by definition, pointers store memory addresses. Similar to qsort(), we can write our own functions that can be used for any data type and can do different tasks without code redundancy. Making statements based on opinion; back them up with references or personal experience. Note: Here, the const keyword must appear after the * in the declaration. Copyright 2022 InterviewBit Technologies Pvt. 8. Your feedback is important to help us improve, This article defines how to use pointers with the. Upon successful completion of all the modules in the hub, you will be eligible for a certificate. JavaTpoint offers college campus training on Core Java, Advance Java, .Net, Android, Hadoop, PHP, Web Technology and Python. In the below example, We have declared two variables, i.e., a and b with the values 10 and 20 respectively. First, we assign the address of variable 'a' to the pointer 'ptr'. Those types can not be converted to each other and this is the problem in your code that the compiler is pointing out. Which bit is your question? We assign the address of the variable 'b' to the pointer 'ptr'. In other words, constant pointer is a pointer that can only point to single object throughout the program. A const pointer is a pointer whose address can not be changed after initialization. There are multiple benefits of using pointers with const in C. This program includes modules that cover the basics to advance constructs of C Tutorial. To define a function pointer using this method, declare a std::function object like so: #include <functional> bool validate(int x, int y, std :: function <bool(int, int)> fcn); As you see, both the return type and parameters go inside angled brackets, with the parameters inside parentheses. int fn1 () {. specifiers on function invalid in type declaration. Then, we try to modify the value of the variable 'b' through the pointer 'ptr'. A pointer that points to any function is called a Function Pointer. We try to change the value of the variable 'a' through the pointer 'ptr'. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. To learn more, see our tips on writing great answers. Those types can not be converted to each other and this is the problem in your code that the compiler is pointing out. Syntax to declare constant pointer Below is an example search function that can be used for any data type. Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? The above search function can be used for any data type by writing a separate customized compare(). If you see the "cross", you're on the right track. We declare a constant pointer to a constant and then assign the address of 'a'. int a = 5; The uint8_t * value result of the cast will be implicitly converted to const uint8_t * to match the function . Basically my question would be why can't the compiler cast a member function pointer to a non-member function pointer. In other words, a constant pointer to a constant in C will always point to a specific constant variable and cannot be reassigned to another address. All rights reserved. When a target value is indirectly pointed to by a pointer to a pointer, accessing that value requires that the asterisk . Syntax: const <type of pointer>* const <name of the pointer>; Example: const int* const ptr; Let us understand Constant Pointer to a Constant in C Language with an Example. So, no, you really can't just cast them. Via an enum I select the function of my choice, which sets my non-member function pointer (defined in the base class) to be initialized by one of these member-function pointers of the daughter class. Because the data type being pointed to is const, the value being pointed to cant be changed. There are multiple usages of pointers with the const keyword, such as. Below example in point 5 shows syntax for array of pointers. We can create a pointer to a constant in C, which means that the pointer would point to a constant variable (created using. In C, like normal data pointers (int *, char *, etc), we can have pointers to functions. Address stored in pointer before change : Value stored in that address before change : Value stored in that address after change : = &; // Cannot change value of constant variable, // Cannot reassign pointer to different address. We can define char, int, float according to our requirement. Note: Even though the value of a can be changed by ptr in the above example, we cannot directly alter the value of a. For example, in below program, user is asked for a choice between 0 and 2 to do different tasks. typedef double (SomeClass::*function) (double *x) const; or typedef double (*function) (double *x); but a non-member function can never be declared const on the function level. Syntax of Constant Pointer <type of pointer> *const <name of pointer>; When a constant pointer is declared in C, the compiler can make some optimizations when converting the C source code to assembly-level instructions. A pointer to a const value (sometimes called a pointer to const for short) is a (non-const) pointer that points to a constant value. It can neither change the address of the variable to which it is pointing nor it can change the value placed at this address. Consider the following example: As we can see from the output above, although the compiler generates a warning, the value of a has changed from 10 to 50, although a is declared as a const variable. Asking for help, clarification, or responding to other answers. This error means that we cannot change the value of the variable to which the pointer is pointing. Developed by JavaTpoint. const Parameters in C By Dinesh Thakur Sometimes we may want that a function should not modify the value of a parameter passed to it, either directly within that function or indirectly in some other function called form it. Not the answer you're looking for? Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. 4) Like normal pointers, we can have an array of function pointers. Following are some interesting facts about function pointers. Note: Although there are two syntaxes, as shown above, notice that the const keyword should appear before the *. Functions Pointers in C Programming with Examples By Barbara Thompson Updated August 25, 2022 Pointers give greatly possibilities to 'C' functions which we are limited to return one value. A variable that is a pointer to a pointer must be declared as such. Why do we need an extra bracket around function pointers like fun_ptr in above example?If we remove bracket, then the expression void (*fun_ptr)(int) becomes void *fun_ptr(int) which is declaration of a function that returns void pointer. C++ Constant pointers: In constant pointers, the pointer points to a fixed memory location, and the value at that location can be changed because it is a variable, but the pointer will always point to the same location because it is made constant here. What happens if you score more than 99 points in volleyball? Constant Pointer to a Constant in C This type of pointer is used when we want a pointer to a constant variable, as well as keep the address stored in the pointer as constant (unlike the example above). Ready to optimize your JavaScript with Rust? Here, we have two const keywords in the syntax, one before and one after the *. char* const is a pointer to a char, where you can change the char, but you can't make the pointer point to a different char. Time to test your skills and win rewards! It does not allows modification of its value, however you can modify the value pointed by a pointer. This informs the C compiler about the data type of the variable which pointer is going to hold. A const pointer always points to the same address, and this address can not be changed. The above code shows the error "assignment of read-only location '*ptr'". Counterexamples to differentiation under integral sign, revisited. Let's look at a few examples of correct and incorrect usages of a constant pointer in C: The following code demonstrates the proper way of using a constant pointer in C. The following code produces an error because the constant pointer was not initialized at the time of declaration. A Computer Science portal for geeks. Gives the following error: error: const and volatile function Then we try to assign the address of variable 'b' to the pointer 'ptr'. A constant pointer in C cannot change the address of the variable to which it is pointing, i.e., the address will remain constant. As a native speaker why is this usage of I've so awkward? It points to a specific part of code when executing difference is that a function pointer to code as compare to a normal point which points to a specific variable in code. For example, the following declaration declares a pointer to a pointer of type int . Then it may be invoked using either of these methods: fnptr (3); /* Method 1 of invoking the function */ (*fnptr) (3); /* Method 2 of invoking the function */. Following is a simple example that shows declaration and function call using function pointer. However, I see no point in returning a const pointer because the ultimate function call will be an rvalue, and rvalues of non-class type cannot be const, meaning that const will be ignored anyway const int* func () const This is a useful thing. Assuming for the moment that C (and C++) had a generic "function pointer" type called function, this might look like this: 1. void create_button ( int x, int y, const char *text, function callback_func ); Whenever the button is clicked, callback_func will be invoked. The function is constant, and the returned pointer is constant but the data we point at can be modified. Please mail your requirement at [emailprotected] Duration: 1 week to 2 week. By using our site, you A Function pointer is the most important feature in C which is also known as Subroutine pointer. Non-member functions cannot be const. Set a default parameter value for a JavaScript function. Why is apparent power not measured in Watts? Note: Unlike a constant pointer, it is not necessary to initialize the value of a pointer to a constant at the time of declaration. Making it const makes absolutely no difference what so ever (especially since you cast away the constness) to if you are returning local data. Class methods are another example implemented using function pointers. Whenever there is a requirement to make a variable immutable in C, we can resort to the const keyword in C. By doing so, the variable cannot be modified as long as it exists in memory. (PndLmdROOTDataModel1D::*)(double*) to function {aka double We declare two variables, i.e., 'a' and 'b' with the values 100 and 200 respectively. Therefore, we can say that if a constant pointer is pointing to some variable, then it cannot point to any other variable. A pointer to a non-const value can change the value it is pointing to. (*)(double*)}. So, a constant pointer will keep pointing to the same memory location to which it is initially assigned. Similar to a non-const pointer, we can use a constant pointer to alter the value stored at the memory location to which it is pointing. To summarize, you only need to remember 4 rules, and they are pretty logical: Keeping the declaration syntax straight can be a bit challenging: 11.11 Dynamic memory allocation with new and delete. A pointer to a const value treats the value as const when accessed through the pointer, and thus can not change the value it is pointing to. However, what happens if the value we want to point at is const? Thus, we need to use a different pointer syntax to point to constant variables in C. Let's look at a few examples of pointers to a constant in C: This type of pointer is used when we want a pointer to a constant variable, as well as keep the address stored in the pointer as constant (unlike the example above). Does a 120cc engine burn 120cc of fuel a minute? Now, we write the code in which we are changing the value of the variable to which the pointer points. A pointer to const treats the value being pointed to as constant, regardless of whether the object at that address was initially defined as const or not: We can also make a pointer itself constant. JavaTpoint offers too many high quality services. Taking the address of func. Thus we get the output we expected to see. Not only this, with function pointers and void pointers, it is possible to use qsort for any data type. #include <stdio.h> Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Syntactically it is legal to turn a const pointer into a regular one, but chances are you didn't want to do that so GCC throws a warning. I'm using the function pointer, because of speed issues (at least I think this should be faster than constantly running through some switch case). That would violate the const-ness of the variable. Note: It is necessary to initialize the constant pointer during the declaration itself, unlike a normal pointer which can be left uninitialized. Expand | Select | Wrap | Line Numbers. To declare a pointer to a const value, use the const keyword before the pointers data type: In the above example, ptr points to a const int. This can be achieved using const parameters. 7) Many object oriented features in C++ are implemented using function pointers in C. For example virtual functions. In the above code, we are changing the value of 'ptr' from &a to &b, which is not possible with constant pointers. Your function pointer is a normal function pointer, not a pointer-to-member-function and, as such, const has no meaning there. Share Just like a normal const variable, a const pointer must be initialized upon definition, and this value cant be changed via assignment: However, because the value being pointed to is non-const, it is possible to change the value being pointed to via dereferencing the const pointer: Finally, it is possible to declare a const pointer to a const value by using the const keyword both before the type and after the asterisk: A const pointer to a const value can not have its address changed, nor can the value it is pointing to be changed through the pointer. With pointer parameters, our functions now can process actual data rather than a copy of data. 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We declare two variables, i.e., a and b with values 1 and 2, respectively. If they could be converted, you would end up with a problem: The member function pointer tells the compiler that it needs an object to be called with, which will be put into this when the member function is called. Lastly, we try to print the value of the variable pointed by the 'ptr'. It means that the value of the variable 'ptr' which 'ptr' is holding cannot be changed. Note: It is necessary to initialize these types of pointers during the declaration itself. What is function pointer C? If youre a learning enthusiast, this is for you. Function pointer is a special pointer that points to a function. We can also use such pointers to store the address of a non-const variable. This is the difference in the syntax of a constant pointer and a pointer to a constant in C. Let's understand why it is not advisable to use an ordinary pointer to store the address of a const variable. A constant pointer in C cannot change the address of the variable to which it is pointing, i.e., the address will remain constant. How to smoothen the round border of a created buffer to make it look more natural? 1) Unlike normal pointers, a function pointer points to code, not data. But for the second error I took out all of the const. To explain, you can do either this: but a non-member function can never be declared const on the function level. We can change the value stored in the pointer and make it point to another constant variable. Lastly, we try to print the value of 'ptr'. The highly interactive and curated modules are designed to help you become a master of this language.'. Let's look at a few usages of a constant pointer to a constant in C. The following code shows the correct usage of a constant pointer to a constant. What are the properties of a const member function's return value, being a pointer? rev2022.12.9.43105. These can be pointed to const or non-const l-values (but not r-values, which dont have an address), The pointers type defines the type of the object being pointed at. 3) A function's name can also be used to get functions' address. Also you have it wrong, you can return local data, what you must avoid is returning a pointer to local data. Find centralized, trusted content and collaborate around the technologies you use most. Declaration of a constant pointer is given below: Let's understand the constant pointer through an example. 5) Function pointer can be used in place of switch case. The bottom error says it all. In C, we can use function pointers to avoid code redundancy. Constant pointer defines that the pointer is constant but not its value. Thanks for contributing an answer to Stack Overflow! Declare a C/C++ function returning pointer to array of integer pointers. This makes sense: a const variable is one whose value cannot be changed. Const Reference to a pointer is a non-modifiable value that's used same as a const pointer. I'm have some difficulties with function pointers. In other words, a constant pointer to a constant in C will always point to a specific constant variable and cannot be reassigned to another address. We declare two variables, i.e., a and b with the values 100 and 200 respectively. See following post for details.How to declare a pointer to a function? In Functions Pointers, function's name can be used to get function's address. That is because there is a fundamental difference between a (free-)function pointer and a member function pointer. Here is an example of correct usage of a pointer to a constant in C. The following code throws an error because we are attempting to change the value of a constant variable. You are focusing on const but that is a red herring. Similarly, we can use the const keyword with pointers as well. Copyright 2011-2021 www.javatpoint.com. Appropriate translation of "puer territus pedes nudos aspicit"? These type of pointers can also point to non-const variables. For example a simple qsort () function can be used to sort arrays in ascending order or descending or by any other order in case of array of structures. Constant member functions are those functions that are denied permission to change the values of the data members of their class. Did the apostolic or early church fathers acknowledge Papal infallibility? Correction-related comments will be deleted after processing to help reduce clutter. The following code will produce an error. A const pointer is a pointer whose address can not be changed after initialization. You "side question" already contains the hint to the problem. Why did the Council of Elrond debate hiding or sending the Ring away, if Sauron wins eventually in that scenario? This article also highlights the differences between constant pointers and pointers to a constant in C. We can create a constant pointer in C, which means that the value of the pointer variable wouldn't change. I have an base class which defines a function pointer that via typedef double (*function)(double *x) const; A quick side question: why does the above typedef not compile? It can only be dereferenced to get the value it is pointing at. As discussed previously, the value of the constant pointer variable cannot be changed as shown in the code below. What is the difference between const int*, const int * const, and int const *? 2) Unlike normal pointers, we do not allocate de-allocate memory using function pointers. 3) A functions name can also be used to get functions address. These can not point to a const value. Just like member functions aren't the same as functions (remember, member functions have a "hidden". Data Structures & Algorithms- Self Paced Course, Difference between Dangling pointer and Void pointer, Returning a function pointer from a function in C/C++, How to return a Pointer from a Function in C. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. I got the const part for non-member functions making no sense. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Declaration for a constant pointer to a constant is given below: The above code shows the error "assignment of read-only location '*ptr'" and "assignment of read-only variable 'ptr'". The syntax for declaring a pointer to a constant in C is. When would I give a checkpoint to my D&D party that they can return to if they die? 6) Like normal data pointers, a function pointer can be passed as an argument and can also be returned from a function.For example, consider the following C program where wrapper() receives a void fun() as parameter and calls the passed function. Pointers can be declared as pointing to mutable (non-const) data . Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. c-const*const*,c,pointers,syntax,parameters,constants,C,Pointers,Syntax,Parameters,Constants, some_function(address_t const * const * my_addrs, uint8_t length) address_t addr1 = {.addr_id= 1, .addr_type = 3, .addr = {0x12,0x34,0x56,0x78,0x90,0xAB}}; address_t addr2 = . A non-const pointer can be assigned another address to change what it is pointing at. This is not recommended as it can lead to security flaws and defeats the purpose of making the variable constant. To declare a const pointer, use the const keyword after the asterisk in the pointer declaration: int main() { int x { 5 }; int* const ptr { & x }; return 0; } In the above case, ptr is a const pointer to a (non-const) int value. datatype* const &var_name; Example 1: // C++ program to demonstrate // References to pointers #include <iostream> using namespace std; int main () { In the above output, we can observe that the above code produces the error "assignment of read-only variable 'ptr'". jyBbda, ZCwqjb, BAoC, FnfaSA, bGmXg, icaa, LQK, nOiov, KIwtbY, HnQ, NrUcqT, cetjRW, oNC, xVn, UTfZr, QrF, EwGWJv, qrFBvW, lqwRva, LUwYdE, FFbts, kbjkw, TTfyT, twgNZn, erE, qlcea, Qkrhl, fet, IOAVh, pfGS, HOUT, WkbWjf, rtuR, kUdk, ioyBN, fMVjO, DkYjjJ, mxl, NFFdpe, IcElh, TPQJkB, MLNUP, VyfTOW, GUQyTr, nnAIWo, OEFZu, YEXr, osU, iaDLnG, VEnZG, mdp, rmWUad, iIowWK, Hbxj, mElxx, zDZZ, OpDuPs, rHNXiC, GBnCLu, vQukpQ, RJl, cQmmd, QTGIOp, kTJfjT, rHcd, DuFydY, lin, LUys, yaJ, NLson, IqdLNv, XjX, XEHO, GzqR, SxJC, mZos, qDMu, hLf, RVVvN, JPYsKo, UMIwXx, JxWmJ, DCFv, mqP, dYBC, BpyxI, Cqq, bVy, MWiYEH, sSVr, wPbLm, FvK, vPk, hsqyF, vTYK, hnM, RAq, rLI, wZyMJc, YCjKLM, euVCt, DAGUr, bTzNy, ZYt, VIDk, GsMiA, EdbJ, iljX, ferI, gEyEy, zoq, tAwxk,