1. Dynamic Memory
A whole heap of fun…

2. Review: The Stack C++ allocates variables on a stack
All memory that might be used in function allocated at one time
Address
Identifier
Value
116
115
114
113
112
111
110
109
108
107
106
105
104
103
102
101
100

3. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(6); int z = 5; bar(); }
Address
Identifier
Value
116
115
114
113
112
111
110
109
108
107
106
105
104
103
102
101
100

4. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116 ??
115
114
113
112
111 z
110
109
108
107 y
106
105
104
103 X
102
101
100

5. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116 ??
115
114
113
112
111 z
110
109
108
107 y
106
105
104
103 X 10
102
101
100

6. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116 ??
115
114
113
112
111 z
110
109
108
107 y 1
106
105
104
103 X 10
102
101
100

7. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116 c ??
115 q 10
114
113
112
111 z
110
109
108
107 y 1
106
105
104
103 X
102
101
100

8. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116 c
'a'
115 q 10
114
113
112
111 z ??
110
109
108
107 y 1
106
105
104
103 X
102
101
100

9. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116
'a'
115 10
114
113
112
111 z ??
110
109
108
107 y 1
106
105
104
103 X
102
101
100

10. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116
'a'
115 10
114
113
112
111 z 5
110
109
108
107 y 1
106
105
104
103 X
102
101
100

11. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116
'a'
115 x 10
114
113
112
111 z 5
110
109
108
107 y 1
106
105
104
103 X
102
101
100

12. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116
'a'
115 x 8
114
113
112
111 z 5
110
109
108
107 y 1
106
105
104
103 X 10
102
101
100

13. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116
'a'
115 8
114
113
112
111 z 5
110
109
108
107 y 1
106
105
104
103 X 10
102
101
100

14. Review: The Stack
void foo(int q) { if(true) { char c = 'a'; } } void bar() { int x = 8; } int main() { int x = 10; int y = 1; foo(x); int z = 5; bar(); }
Address
Identifier
Value
116
'a'
115 8
114
113
112
111 5
110
109
108
107 1
106
105
104
103 10
102
101
100

15. What will this do? getPointerToTen Initialize a variable
Makes a pointer to it
Returns that pointer
Main prints twice

16. The Stack C++ allocates variables on a stack
int* getPointerToTen() { int x = 10; int* px = &x; return px; }
int main() { int* pTen = getPointerToTen(); cout << *pTen << endl; }
Address
Identifier
Value
116
115
114
113
112
111
110
109
108
107
106
105
104
103
pTen ??
102
101
100

17. The Stack C++ allocates variables on a stack
int* getPointerToTen() { int x = 10; int* px = &x; return px; }
int main() { int* pTen = getPointerToTen(); cout << *pTen << endl; }
Address
Identifier
Value
116
115
114
113
112
111 px
104
110
109
108
107 x 10
106
105
103
pTen ??
102
101
100

18. The Stack C++ allocates variables on a stack
int* getPointerToTen() { int x = 10; int* px = &x; return px; }
int main() { int* pTen = getPointerToTen(); cout << *pTen << endl; }
Address
Identifier
Value
116
115
114
113
112
111
104
110
109
108
107 10
106
105
103
pTen
102
101
100

19. ???
Pointers to items on stack may go bad