Many a times one of the challenges a beginner faces is with the use of const keyword. It comes handy when one understands the exact use of it. Const keyword changes its meaning depending on where it is being used. Below I give all possible use of the keyword.
Normal integer variable:
int intValue // integer variable
As function parameter:
Void testFunc(int intValue) {
// modification of intValue is possible
intValue = 10;
}
Here the value passed to testFunc() is copied to a separate memory area, which can be accessed through intValue
Pointer to integer variable:
int *ptrToInt // pointer to integer variable
As function parameter:
void testFunc(int *ptrToInt) {
int a = 10;
cout << ptrToInt << endl; //prints the memory address of passed variable
cout << *ptrToInt << endl;
ptrToInt = &a; //assigning address of variable ‘a’ to ptrToInt ie. Modification of ptrToInt is possible
cout << ptrToInt << endl; //prints the memory address of variable a
cout << *ptrToInt << endl; //prints the value of a ie. 10
}
Constant integer value:
int const constInt // constant variable, cant be modified
const int constInt // also
As function parameter:
void testFunc(int const constInt) {
//constInt can’t be changed here
}
Pointer to constant integer:
int const *ptrToConstInt // pointer to a constant integer variable
const int *ptrToConstInt // also
As function parameter:
void testFunc(const int *ptrToConstInt) {
const int a = 10;
ptrToConstInt = &a;
cout << ptrToConstInt << endl; // prints the memory address of variable a
cout << *ptrToConstInt << endl; // prints the value of a ie. 10
}
Constant pointer to an integer:
int *const constPtrToInt // constant pointer to integer variable
As function parameter:
void testFunc(int *const constPtrToInt) {
//constPtrToInt cant be changed but the value it points to, can be altered
*constPtrToInt += 10; //since it points to, is a normal integer value
}
Constant pointer to constant integer:
int const * const constPtrToConstInt // constant pointer to constant integer value
As function parameter:
void testFunc(int const *const constPtrToConstInt) {
//here the value of constPtrToConstInt as well as the value it points to, both is immutable
}
MORE USE OF ‘const’ KEYWORD:
Constant pointer to a constant pointer to an integer:
int * const * const const_ptr_to_const_ptr_to_int
Constant pointer to a pointer to a pointer:
int ** const const_ptr_to_ptr_to_int
Pointer to a constant pointer to an integer:
int * const * ptr_to_const_ptr_to_int
Pointer to a pointer to an integer:
int ** ptr_to_ptr_to_int
Tip: “int const” and “const int” are same. So if the line contains any of these two, understand that the final part is “integer constant” take the rest of the line and read backwards,
* ==means==> ‘pointer to’
* const ==means==> ‘constant pointer to’
Multiple ‘*’ ==means==> that number of ‘pointer to’
Hope this post was helpful to you… 🙂
WikiSree 