Access Private Members in C++
Just a proof-of-concept, not really much practical use. Also this tells us: if you REALLY want to access something, just get a pointer and start casting, lol.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 | /** * Output: * * $ g++ -w -O0 AccessPrivateField.cc * $ ./a.out * a: 0 * a: 9999 * A::secretFunc called (this depends on your platform and compiler, probably won't work) * $ */ #include <iostream> #include <cstdio> class A { private: int a; public: A() : a(0) {}; void print(); private: void secretFunc(); }; void A::print() { std::cout << "a: " << a << std::endl; } void A::secretFunc() { std::cout << "A::secretFunc called" << std::endl; } int main(int argc, char **agrv) { A *myA = new A(); myA->print(); // Compilation error: cannot access private member variable // myA->a = 9999; // This is how you do it *((int *) myA) = 9999; myA->print(); // try access private member function // dirty trick to convert pointer-to-member to a local address char buf[100]; std::sprintf(buf, "%p", &A::print); unsigned long ptrAddress; std::sscanf(buf, "%lx", &ptrAddress); // the -0x30 offset is retreived AFTER compilation, // and it depends on the length of generated code for A::print // which renders this technique useless in practice void (*secretFuncPtr)(A*) = (void (*)(A*)) (ptrAddress - 0x30); secretFuncPtr(myA); return 0; } |
Tags: C++
Programming | softboysxp, February 27, 2010 11:02 pm | 
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