c / intermediate
Snippet
Const Correctness with Pointer Variations
Understanding where 'const' is placed is vital for API safety. A pointer to a constant ensures the data won't be modified, while a constant pointer ensures the pointer itself always points to the same memory location.
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#include <stdio.h>void demonstrate_const() {int val1 = 10, val2 = 20;const int* p1 = &val1; // Pointer to constant int// *p1 = 15; // Error: cannot modify datap1 = &val2; // OK: can change addressint* const p2 = &val1; // Constant pointer to int*p2 = 15; // OK: can modify data// p2 = &val2; // Error: cannot change addressconst int* const p3 = &val1; // Constant pointer to constant int// p3 = &val2; // Error// *p3 = 15; // Error}
Breakdown
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const int* p1
The data being pointed to is read-only through this pointer.
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int* const p2
The memory address stored in the pointer is fixed and cannot be changed after initialization.