Example
The prefixes ++ and * have the same precedence and are right to left-associative. Postfix ++ has higher precedence than prefix ++ and *and is associative from left to right. Look at the example below to see the difference between ++*p, *p++, and *++p.
Code:
#include <stdio.h>
int main() {
int nums[] = {10, 20, 30, 40, 50};
int *p = nums; //pointer storing the address of nums array
int var;
var = ++*p; //value at index 0 incremented by 1
printf("nums[0] = %d, nums[1] = %d, *p = %d, var = %d \n",
nums[0], nums[1], *p, var);
var = *p++; //value of index 0 stored in var and pointer get inc
printf("nums[0] = %d, nums[1] = %d, *p = %d, var = %d \n",
nums[0], nums[1], *p, var);
var = *++p; //pointer address get inc and then value is stored
printf("nums[0] = %d, nums[1] = %d, *p = %d, var = %d \n",
nums[0], nums[1], *p, var);
return 0;
}
You can also try this code with Online C Compiler
Output:
nums[0] = 11, nums[1] = 20, *p = 11, var = 11
nums[0] = 11, nums[1] = 20, *p = 20, var = 11
nums[0] = 11, nums[1] = 20, *p = 30, var = 30
By recalling simple principles concerning postfix ++, prefix ++, and * (dereference) operators, the result of the programs mentioned above and all similar programs may be anticipated.
1) The prefixes ++ and * have the same precedence. Both have right-to-left associativity.
2) Postfix ++ has a greater precedence than both * and prefix ++. Postfix ++ associativity is left to right.
The compiler searches for associativity because ++*p contains two operators with the same precedence. Operator associativity is right to left. As a result, the expression is handled as ++(*p). As a result, the first program's output is "nums[0] = 11, nums[1] = 20, *p = 11."
Postfix ++ takes priority over *, the expression *p++ is evaluated as *(p++).
As a result, the second program's output is "nums[0] = 11, nums[1] = 20, *p = 20."
*++p contains two operators with the same precedence, the compiler searches for associativity. Operator associativity is right to left. As a result, the expression is interpreted as *(++p). As a result, the third program's output is "nums[0] = 11, nums[1] = 20, *p = 30."
Also See, Sum of Digits in C and Short int in C Programming
Frequently Asked Questions
What is the difference between i++ and ++i?
There are two types of ++ operators: pre and post-increment. i++ is post increment where the value of i will be used first and then increment. ++i is pre-increment, and it will first increment the value of i and then use it.
What is the dereference operator?
* operator is the dereference operator. Dereferencing a pointer occurs when this operator (*) is used with the pointer variable. When a pointer is dereferenced, the value of the variable pointed by the pointer is returned.
What is a pointer?
A pointer is an object that contains the address of a memory location i.e. the memory location's direct address. A pointer, like any other variable or constant, must be declared before it may be used to hold any variable address.
Conclusion
In this article, we have extensively discussed the difference between ++*p, *p++, and *++p in the C programming language.
We hope this blog has helped you enhance your knowledge regarding the pointers in the C language. Some official documentation on C programming language that can help you improve your understanding is C documentation.
Check out this problem - Longest Common Prefix
If you would like to learn more, check out our articles on pointers, learn pointers, and pointers in C.
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