INFO: Why pointer1++ = pointer2 Is Not ProperArticle ID: Q38218 The information in this article applies to:
SUMMARYThe following statement is not correct because the post-increment operator (++) has higher precedence than the assignment operator (=): pointer1++ = pointer2; The following statement pointer1++ = pointer2 ; is equivalent to the following statement: (pointer1++) = pointer2 ; MORE INFORMATIONAs defined by the post-increment operation, the result of evaluating the expression (pointer1++) is NOT an lvalue; therefore, (pointer1++) cannot be used as a left operand of the assignment operator. However, a statement such as the following is correct: *(pointer1++) = *pointer2; The above statement is equivalent to: *pointer1++ = *pointer2; This statement is correct because although (pointer1++) is not an lvalue, it can be used for indirection and *(pointer1++) is an lvalue. It is very important to understand the difference between the value of the expression (pointer1++) and the value of pointer1. Although (pointer1++) has higher precedence in the above statements, the result of evaluating (pointer1++) has the old value that pointer1 had before the evaluation of the expression (pointer1++). Because of the side effect of the post-increment operator, the evaluation of (pointer1++) causes the value of pointer1 to be incremented by one only after the rest of the statement has been evaluated. In other words, as an address, (pointer1++) points to the same memory location as pointer1 used to. Therefore, *pointer1++ or *(pointer1++) represents the same object as *pointer1 used to. The following example has the effect of assigning "a" to memory offset location 0x100, then incrementing ptr1 to point to memory offset 0x101: char * ptr1 = 0x100; /* ptr1 points to memory offset 0x100 */ *ptr1++ = 'a'; /* ptr1 points to memory offset 0x101 */ Keywords : kbLangC kbVC Version : MS-DOS:5.1,6.0,6.00a,6.00ax,7.0; WINDOWS:1.0,1.5,1.51,1.52; WINDOWS NT:1.0,2.0,2.1,4.0,5.0 Platform : MS-DOS NT WINDOWS |
Last Reviewed: August 28, 1997 |
