c++ - Is const a lie? (since const can be cast away) -

possible duplicate:
sell me on const correctness

what usefulness of keyword const in c or c++ since it's allowed such thing?

void const_is_a_lie(const int* n) {      *((int*) n) = 0; }  int main() {     int n = 1;     const_is_a_lie(&n);     printf("%d", n);     return 0; } 

output: 0

it clear const cannot guarante non-modifiability of argument.

const promise make compiler, not guarantees you.

for example,

void const_is_a_lie(const int* n) {      *((int*) n) = 0; }  #include <stdio.h> int main() {     const int n = 1;     const_is_a_lie(&n);     printf("%d", n);     return 0; } 

output shown @ http://ideone.com/ejogb is

1

because of const, compiler allowed assume value won't change, , therefore can skip rereading it, if make program faster.

in case, since const_is_a_lie() violates contract, weird things happen. don't violate contract. , glad compiler gives keeping contract. casts evil.