So let's take the p++ part first. postfix and prefix has higher precedence than dereference so, *ptr++ here post increment ptr and then pointing to new value of ptr, *++ptr here Pre Increment fist then pointing to new value of ptr, ++*ptr here first get the value of ptr pointing to and increment that vlaue, ++*p means that you are trying to increment the ASCII value of *p which, you cannot increment the value 'cause it's a constant so you would get an error. "int *const" means that just the variable value itself (the pointer) cannot be changed. It is visible from the point of definition to the end of the program. Did an AI-enabled drone attack the human operator in a simulation environment? I was looking at C99 specification (N1256.pdf) which says on (p.11506): "The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer, but ptr_to_constant itself may be changed to point to another object. It is visible throughout the function. 1 ptr is the same across all three; it's a variable. So now the p++ part of *p++ has been evaluated; it's the current value of p. Then the * part happens. You will be notified via email once the article is available for improvement. You wanted while(*p) and printf("%c", *p++); Great questions for interview. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. It's true there was interesting discussion on possible reasons for parsing but it does not address my trouble. There seems to be some confusion. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. So the value of the object pointed to by ptr is retrieved, then ptr is incremented. First, we assign the address of variable 'a' to the pointer 'ptr'. What is the value of 'H'++? #include<stdio.h> int main() { int num = 300; int *ptr;//uninitialized pointer.. must be initialized ptr = &num; printf(" num = %d ptr = %p and data on ptr : %d \n",num,ptr,*ptr); *ptr = *ptr + 1;//*ptr means value/data on the address.. so here value gets incremented printf(" num = %d ptr = %p and data on ptr : %d \n",num,ptr,*ptr); /** observe . In this case, because it is a complex type it++ maybe have side effects because of the temp creation. ++*ptr : only 1 instruction (INC) is used, directly value gets changed in single shot. That is the primary effect: The compiler must help the programmer avoid mistakes by diagnosing these misuses of things qualified with const. In Germany, does an academia position after Phd has an age limit? A const pointer always points to the same address, and this address can not be changed. int * ptr - ptr is a pointer to int; int const * ptr - ptr is a pointer to constant int; int * const ptr - ptr is a constant pointer to int; const int * const ptr - ptr is a constant pointer to const int; Now the first const can be on either side of the type so: const int * ptr equal to int const * ptr I was asking the about the second form given in the standard vs one that is not given the standard. Reason I mention in comments. Then, as a side effect, that 'H' is going to be incremented to 'I'. C++ code const int* p = . in the declaration, then the object pointed by the pointer is variable, but the pointer *ptr = *ptr + 1 : here first value gets incremented(INC) and then assigned(MOV). c) Array Incrementing pointer (ptr++) and (*ptr++), Pointer expressions: **ptr++, *++*ptr and ++**ptr use, Difference between *ptr += 1 and *ptr++ in C, pointer arithmetic: *p++ and (*p)++ and more, difference in incrementing pointer with ** and without in C, Noisy output of 22 V to 5 V buck integrated into a PCB. Find centralized, trusted content and collaborate around the technologies you use most. ++*ptr increases arr[i] by one and evaluates to its increased value; the pointer ptr is left untouched. Correction-related comments will be deleted after processing to help reduce clutter. B. What happens when you add 1 to 'H'? Hence, neither the pointer should point to a new address nor the value being pointed to should be changed. If you have: because i++ evaluates to i before the increment. What are philosophical arguments for the position that Intelligent Design is nothing but "Creationism in disguise"? There's also one more, but you'd need parentheses to write it: The rest you can figure out yourself; it was also answered by @Jaguar. When we say "pointer to a char", what does that mean? Is there a grammatical term to describe this usage of "may be"? *++ptr : Same as first one here also address gets incremented but its pre increment. Insufficient travel insurance to cover the massive medical expenses for a visitor to US? Our C questions and answers focuses on all areas of C programming 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. All right, but in those last two cases, why do I need. I'll absolutely agree with the first part of the answer. C #include <stdio.h> int main (void) { int i = 10; int j = 20; int *ptr = &i; printf("*ptr: %d\n", *ptr); Answer: A Can I increase the size of my floor register to improve cooling in my bedroom? and then the consequence of violating a constraint is that the compiler must produce a diagnostic message, per C 2018 5.1.1.3 1: A conforming implementation shall produce at least one diagnostic message if a translation unit contains a violation of any syntax rule or constraint. what matters is not precedence: the two operators are identical in precedence. Postfix expression side effects. const int* const is a constant pointer to constant integer This means that the variable being declared is a constant pointer pointing to a constant integer. 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. The more you learn, the less you pay. Postfix has higher precedence, but prefix has the same precedence as dereference. Here's a detailed explanation which I hope will be helpful. the correct syntax for initialization of pointer ptr with string "programming"? [What] does const do in this case - const int *ptr; Primarily what const in that declaration does is require the compiler to warn you about certain misuses of the pointer. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Pointers as Constant : there are no of ways by which you can make pointers as constant, few I am mentioning here. Not the answer you're looking for? What does the loop condition *p++ mean? A. So a statement like *p_int = 3; will fail. 576), AI/ML Tool examples part 3 - Title-Drafting Assistant, We are graduating the updated button styling for vote arrows. By using our site, you I couldn't help but toggling my accepted answer. The above snippet wont compile -- we cant set a normal pointer to point at a const variable. One way to remember the syntax (according to Bjarne Stroustrup) is the spiral rule- The rule says, start from the name of the variable and move clockwise to the next pointer or type. B. The declaration int (* p) [5]; means A. p is one dimensional array of size 5, of pointers to integers. Are non-string non-aerophone instruments suitable for chordal playing? Can I trust my bikes frame after I was hit by a car if there's no visible cracking? If *p++ evaluates to 'H', why doesn't that 'H' print in the above code? These questions are taken from a real written exam and some parts are taken from an interview. Effectively, this implies that a constant pointer is pointing to a constant value. const int *ptr; Online Test, 1) What will be the output of the program ? . D. None of these. 1) What will be the output of the program ? What do these three Expressions REALLY mean? Before explaining this lets consider simple example ? b) Pointer which has no value Thx. #include <stdio.h> int main () { char * p = NULL; char * q = 0; if ( p) printf(" p "); else printf("nullp"); if ( q) printf("q\n"); else printf(" nullq\n"); } a) nullp nullq b) Depends on the compiler c) x nullq where x can be p or nullp depending on the value of NULL d) p q View Answer Answer: a In other words, it has the same precedence as the dereference / indirection operator *. What is the difference between char * const and const char *? d) None of these. So you will find questions on basic techniques such as Variables, Operators, Conditional Statement, Functions, and more. a) p is one dimensional array of size 5, of pointers to integers In C, string literals are read-only; attempting to modify them invokes undefined behavior. Remember, 'H'++ evaluates to the current value of 'H'. So the expression *p++ evaluates to 'H'. After all, p is a pointer to one char, not to the entire string. int const * : Point a constant int so its can not be changed. CASE 1 : *ptr++ , *++ptr, *(ptr++) and *(++ptr) : above mentioned all 4 syntax are similar, in all address gets incremented but how address gets incremented that's different. To understand this lets check simple code. Some address ? If the `const' keyword is to the left of the asterisk, and is the only such keyword Every pointer regardless of its type whereas single pointer or pointer to pointer, needs only 2 bytes.Size of pointer and int is 2 bytes in Turbo C compiler on windows 32 bit machine. How to pass a 2D array as a parameter in C? :) Thanks again. 1) Pointer to variable. How much of the power drawn by a chip turns into heat? The "const" keyword modifies different things in these two cases. Uninitialized pointers are known as wild pointers because they point to some arbitrary memory location and may cause a program to crash or behave badly. C. 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By diagnosing these misuses of things qualified with const be incremented to ' '. That ' H ' is a pointer to a new address nor the value pointed! Share private knowledge with coworkers, Reach developers & technologists share private knowledge with coworkers, developers... All three ; it & # x27 ; s a variable, what does that mean a environment! On possible reasons for parsing but it does not address my trouble cant... As first one here also address gets incremented but its pre increment Intelligent design is nothing but Creationism... ( `` % c '', * p++ has been evaluated ; it & x27. Those last two cases the program of ways by which you can make pointers as constant there... ' print in the above code it 's true there was interesting discussion possible! Cases, why do I need I ' I hope will be.! 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