From What does an assignment return? :
An assignment expression has the value of the left operand after the assignment
and this code:
#include <iostream>
using namespace std;
int main() {
int a[5] = { 0,1,2 };
int* a_ptr = a;
int b = (*a_ptr++ = 3); //int *b won't compile
cout << b << endl; //3
}
What is the left operand of =
when evaluating (*a_ptr++ = 3)
?
What's the definition of an operand ? In my mind, an operand is an identifier or name which is aptr
.
int b = (*a_ptr++ = 3);
is grouped as int b = (*(a_ptr++) = 3);
. Note that the parentheses are superfluous; you could have written
int b = *a_ptr++ = 3;
which in many ways makes the result more obvious, since the right-to-left associativity of =
is such that the 3 carries over to the value of b
.
a_ptr++
is an expression equal to a_ptr
but it will point to the second element of the array a
once the whole statement completes. Since you don't make use of that incremented pointer, the ++
is a red-herring, so the statement simplifies to
int b = *a_ptr = 3;
whereupon it's clear that *a_ptr = 3
has the effect of setting the first element of the array a
to 3 and is an expression equal to 3, which is assigned to b
.
The left operand is *a_ptr++
. As per the operator precedence , it's evaluated as
*(a_ptr++)
where the post-increment is sequenced as a side effect, after the execution of the statement. The value of the operand is the result of the statement. So, it's equivalent to
int b = (*a_ptr = 3);
a_ptr++;
That said, in general, Operands are expressions or values on which an operator operates or works. So, it can be
var
, as in int var
)5
or '"Hello"')*a_ptr++
)
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