OOP in C - Inherit (Chinese Version)
by Kai-Feng Chou on Nov 23, 2009
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OOP in C - Inherit (Chinese Version) — Presentation Transcript
- OOP in C Inherit elpam.tw@gmail.com elpam@Taiwan, Taipei, 2008
- LICENSE ● 本投影片授權方式為： – 姓名標示─非商業性─相同方式分享 3.0 台灣版 – http://creativecommons.org/licenses/byncsa/3.0/tw/ ● 所有的範例程式皆為 Public Domain elpam.tw@gmail.com
- About This Slides ● All example was build by – GCC4.1.3 – GLIB1.2.10 – GMAKE3.81 elpam.tw@gmail.com
- C Language Review ● Stack – Caller Function's Address – CPU's Register – Local Value ● Heap (runtime heap) – managed by malloc elpam.tw@gmail.com
- Address Space ● Linux Memory Model – copy from Jserv's STACK Hacking Hello World HEAP elpam.tw@gmail.com
- Function Stack Caller's Address Return Address void Func_B() Local Value { int a,b; /* do nothing*/ } Low void Func_A() int b { Func_B's Stack int a char a; Func_A Func_B(); } char a Func_A's Stack main int main() { Func_A(); } main's stack .... elpam.tw@gmail.com High
- After Review ● 請了解 Callee Stack 裡頭會放置那些東西 ● 請了解 Callee Stack Release 後那些變數會被清 除掉 ● 請確定已正確的了解 Stack 與 Heap 的差別 elpam.tw@gmail.com
- Structure elpam.tw@gmail.com
- Structure (I) /* 11.c */ ● Address + Offset struct A{ int a; int b; – pa = 0x804a008 }; – pa > a == pa + 0 int main() { – pa > b == pa + 4 struct A* pa =malloc(sizeof(struct A)); printf("%x,%x,%xn" ,pa, &(pa>a), &(pa>b) ); free( pa ); #> ./11 } 804a008,804a008,804a00c #> elpam.tw@gmail.com
- ● 所有的東西都是 Memory Address ● > 所代表的意義是 offset ，而這一個數值的大 小可以在 Compiler Time 被決定 elpam.tw@gmail.com
- Structure (II) /* 12.c */ struct A{ Size = 8 byte ● pa == pb int a; int b; }; – pa > c Compile Error struct B{ int a; int b; – pb > c Correct int c; Size = 12 byte }; int main() { struct A* pa =malloc(sizeof(B)); struct B* pb = pa; pa > a = 1; pa > b = 2; #> ./12 pb > c = 3; 1,2,3 #> printf("pb(%d,%d,%d)n" ,pb>a,pb>b,pb>c ); } elpam.tw@gmail.com
- ● Pointer 的 Type 與被 allocate 的記憶體大小是沒 有關係的 ● 請注意我們是如何使用 casting elpam.tw@gmail.com
- /* 13.c */ Structure (III) struct A{ int a; ● }; Casting int main() { struct A* pa = malloc( sizeof(struct A) ); struct B{ struct B* pb = pa; short b; struct C* pc = pa; short c; }; pc > hi_b = 0x12; pc > low_b = 0x34; struct C{ pc > hi_c = 0x56; char low_b; pc > low_c = 0x78; char hi_b; char low_c; printf("pb>b(0x%x) pb>c(0x%x)n",pb>b,pb>c ); char hi_c; printf("pa>a(0x%x)n",pa>a ); }; free( pa ); } elpam.tw@gmail.com
- Structure (III) (cont') ● Memory Casting ● x86 is littleendian pc > hi_b = 0x12; pc > low_b = 0x34; pc > hi_c = 0x56; pc > low_c = 0x78; #>./13 pb>b(0x1234) pb>c(0x5678) pa>a(0x56781234) #> elpam.tw@gmail.com
- Inherit elpam.tw@gmail.com
- C++ Review /* 16.cpp */ class A{ ● Casting to Parent public: int a; }; class B : public A{ public: int b; }; int main() { B b; b . b = 2; A(b) . a = 1 } elpam.tw@gmail.com
- Inherit int main() { ● sizeof(A) = 8 struct B* pb = malloc(sizeof(struct B)); pb > parent . a = 0; ● sizeof(B) = 12 pb > parent . b = 1; pb > c = 2 /* 14.h */ } struct A{ int a; int b; /* 14.c */ Inherit A }; int main() struct B{ { struct A parent; struct A* pa =malloc(sizeof(struct B)); int c; struct B* pb = pa; }; pa > a = 0; pa > b = 1; #>./14 pb > c = 2; pa(1,2) pb(3) } #> elpam.tw@gmail.com
- Inherit & Casting /* 15.c */ ● Casting to Parent int main() { struct B* pb =malloc(sizeof(struct B)); pb > c = 3; struct A* pa = pb; /* 15.h */ pa > a = 1; struct A{ pa > a = 2; int a; int b; printf("pa(%d,%d) pb(%d)n" }; ,pa>a,pa>b,pb>c ); struct B{ } struct A parent; int c; }; #>./15 pa(1,2) pb(3) #> elpam.tw@gmail.com
- Public Member Value in C++ int main() { class A{ B* b = new B; public: int a; b . a = 0; int b; b . b = 1; }; b . c = 2; class B : public A { } public: int c; }; int main() { A* a = new b; a . a = 0; a . b = 1; a . c = 2; /* error */ B(a) . c = 2; /* correct */ } elpam.tw@gmail.com
- Object Inherit ● C Language ● C++ struct A{ class A{ int a; public: int b; int a; }; int b; struct B{ }; struct A parent; class B : public A { int c; public: }; int c; }; elpam.tw@gmail.com
- Type Casting ( 形態轉換 ) ● C Language ● C++ – StructuretoStructure – dynamic_cast ● AddresstoAddress – static_cast – reinterpret_cast – const_cast elpam.tw@gmail.com
- Inherit in C ● C > B > A /* error memory access */ int main() struct A{ { int v1; struct B* pb = malloc(sizeof(B)); int v2; struct C* pc = pb; /* correct */ }; pc > v1 = 0; /* run time error */ struct B{ struct A parent; } int v1; }; struct C{ struct B parent; struct C c; int v1; struct B* pb = &c; /* use B's member */ }; struct A* pb = &c; /* use A's member */ elpam.tw@gmail.com
- Conclusion 我們可以使用 memory casting 的技巧來描述繼承關係 * 因為缺乏語法 (Compiler) 的保護，所以我們必須 要小心的使用 elpam.tw@gmail.com
- Questions ● 建構子 (Constructor) 還有需要嗎 ? ● 但 C++ 的繼承還提供了 Virtual Function, 需要 這樣的功能嗎 ? 該如何實作 ? – 下一個投影片將討論這兩個問題 elpam.tw@gmail.com
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