关于constpointer.doc

PointersA pointer holds the memory address of an object. For a type T, T* is the type pointer to T. For example,int i = 5;int* ptr_to_i = &i; / ptr_to_i holds the address of iint *also_ptr_to_i = ptr_to_i;The type of ptr_to_i is int*. Prefix unary & is the address of operator. It is preferable to writeint *p;rather thanint* p;This is because in the following example:int* p1, p2; / whoops, p2 is not a pointer-to-intp1 is a pointer-to-int while p2 is a plain int. To make both variables pointers, we write this:int *p1, *p2; / p1 and p2 are pointer-to-intDereferencingThe fundamental operation on a pointer is dereferencing. When you dereference a pointer, you get the object that the pointer is pointing to. The dereferencing operator is prefix unary *. For example:char c = w; / c has the value wchar *ptr_to_c = &c; / ptr_to_c holds the address of c char c2 = *ptr_to_c; / dereference-c2 has the value wBy dereferencing a pointer, we can change the value of the object pointed to:char c = x;char *ptr_to_c = &c;*ptr_to_c = y; / c now has the value yNull PointerA pointer with the value zero (0) is a pointer that points to nothing. You must check that a pointer is not a NULL pointer before using it. Consider a function that takes a pointer as an argument:void someFunction(int *p) if( p ) / p is not NULL-ok to use it here else / p is NULL-dont use p as is Pointers and constYou should read pointer declarations from right to left. For example:int *p; p is a pointer to an int.const int *p; p is a pointer to a const int. The const int object cannot be changed via the *const p; p is a const pointer to an int. The int object can be changed by the pointer, but the pointer itself cannot be changed.const int *const p; p is a const pointer to a const int. The const int object cannot be changed by the pointer, and the pointer itself cannot be changed.The following example is from Stroustrup: void f1(char *p) char s = Gorm; const char *pc = s; / pointer to constant pc3 = g; / error: pc points to constant pc = p; / ok char *const cp = s; / constant pointer cp3 = a; / ok cp = p; / error: cp is constant const char *con