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c++cpointers

What happens when a casted pointer has an increment operator?

For example:

int x[100];
void *p;

x[0] = 0x12345678;
x[1] = 0xfacecafe;
x[3] = 0xdeadbeef;

p = x;
((int *) p) ++ ;

printf("The value = 0x%08x", *(int*)p);

Compiling the above generates an lvalue required error on the line with the ++ operator.

Solution

  • The cast creates a temporary pointer of type int *. You can't increment a temporary as it doesn't denote a place to store the result.

    In C and C++ standardese, (int *)p is an rvalue, which roughly means an expression that can only occur on the right-hand side of an assignment.

    p on the other hand is an lvalue, which means it can validly appear on the left-hand side of an assignment. Only lvalues can be incremented.