6.s096. Introduction to C and C++

Transcription

1 6.s096 Introduction to C and C++

2 I know C and C++

3

4 Java Python C C++

5 Java Python C C++

6 Idioms & Best Practices

7 Tom Lieber Kyle Murray Frank Li

8 Damon Doucet Leonid Grinberg Evan Wang Chen Zhao

9

10

11 web.mit.edu/6.s096/

12 Registration, Wait List Grading: -,, + or better passes 70% assignments, 30% project

13 Why?

14 1 You seek performance

15 1 You seek performance zero-overhead principle

16 2 You seek to interface directly with hardware

17 3 That s kinda it

18 C a nice way to avoid writing assembly language directly

19 C++ responds to the demands of maintaining large C projects

20 C++11 responds to the demands of maintaining large C++ projects

21 Maintain power and flexibility of what came before

22 Compilation Today: Pipeline

23 Compilation Today: Pipeline

24 Source Code Program

25 main.c prog int a = gcc -o prog main.c

26 main.c int a = 1; prog int b = 2; gcc -o prog main.c main2.c

27 $ gcc -o prog main.c $./prog Hello, World! $

28 $ gcc -o prog main.c $./prog Hello, World! $ DONE

29 To debug the sausage, one must see how it is made. Someone, probably

30 Main.java int a = 1; Main.class %!(*@ java Main

31 Main.java int a = 1; Main.class %!(*@ java Main main.py a = 1 main.pyc %!(*@ python main.py

32 Main.java int a = 1; Main.class %!(*@ java Main main.py a = 1 main.pyc %!(*@ python main.py main.c main.o prog int a = 1; int a = 1;

33 main.c main.o prog int a = 1; int a = 1; Pre-Process

34 main.c main.o prog int a = 1; int a = 1; Pre-Process Compile

35 main.c main.o prog int a = 1; int a = 1; Pre-Process Compile Link

36 main.c main.o prog int a = 1; int a = 1; Pre-Process main2.o %!(*@ Compile Link

37 Pre-Process Compile Link

38 Pre-Process Compile Link

39 Pre-Process Compile Link

40 #include #define #ifdef

41 rimshot.txt ba-dum chh joke.txt A man walks into a bar. Ouch! #include "rimshot.txt" cpp -P joke.txt

42 output: A man walks into a bar. Ouch! ba-dum chh cpp -P joke.txt

43 double.py #define fosho def #define kthx return #define wutz print These are called macros fosho double(x): kthx x * 2 wutz double(6) cpp -P double.py

44 output: def double(x): return x * 2 print double(6) cpp -P double.py

45 output: def double(x): return x * 2 print double(6) cpp -P double.py python 12 AWESOME cpp -P double.py

46 beer.txt #define beer(x) x bottles of \ beer on the wall... beer(99) beer(98) beer(97)... cpp -P beer.txt

47 beer.txt #define beer(x) x bottles of \ beer on the wall... beer(99) beer(98) beer(97)... cpp -P beer.txt

48 output: 99 bottles of beer on the wall bottles of beer on the wall bottles of beer on the wall cpp -P beer.txt

49 answer.txt What s 7 times 6? #ifdef REVEAL 42 #endif cpp -P answer.txt

50 output: What s 7 times 6? cpp -P answer.txt

51 output: What s 7 times 6???? cpp -P answer.txt

52 #define REVEAL cpp -P answer.txt

53 #define REVEAL or: cpp -P -D REVEAL answer.txt cpp -P answer.txt

54 output: What s 7 times 6? 42 cpp -P -D REVEAL answer.txt

55 answer.txt What s 7 times 6? #ifndef REVEAL 42 #endif cpp -P answer.txt

56 (Fancy) String Substitution

57 How is this used in C?

58 hello.c #include <stdio.h> int main() { printf("hello, World!\n"); return 0; } gcc -E hello.c

59 hello.c * angle brackets -> use the system search path #include <stdio.h> int main() { printf("hello, World!\n"); return 0; } gcc -E hello.c

60 hello.c * angle brackets -> use the system search path #include <stdio.h> int main() { printf("hello, World!\n"); return 0; } gcc -E hello.c

61 output: int printf(const char *,...) attribute (( format ( printf, 1, 2))); int main() { } printf("hello, World!\n"); * pretending printf is all that s defined in stdio.h gcc -E hello.c

62 output: int printf(const char *,...); int main() { } printf("hello, World!\n"); * pretending printf is all that s defined in stdio.h gcc -E hello.c

63 #include is not import pickle import java.io.*;

64 fib.c #define MAX_FIB 20 int fib[max_fib]; int main() { fib[0] = 0; fib[1] = 1; for(int i = 2; i < MAX_FIB; i++) fib[i] = fib[i-1] + fib[i-2]; return 0; } gcc -E fib.c

65 output: int fib[20]; int main() { fib[0] = 0; fib[1] = 1; for(int i = 2; i < 20; i++) fib[i] = fib[i-1] + fib[i-2]; } gcc -E fib.c

66 debug.c #include <stdio.h> int main() { #ifdef DEBUG printf("hello, World!\n"); #endif return 0; } gcc -DDEBUG debug.c -o debug

67 debug.c #include <stdio.h> int main() { printf("hello, World!\n"); return 0; } gcc -DDEBUG debug.c -o debug

68 debug.c #include <stdio.h> int main() { } return 0; gcc debug.c -o debug

69 Pre-Process Compile Link

70 main.c main.o prog int a = 1; int a = 1; Compile

71 Compile Type-checking Linear processing

72 Type-checking int reptile() { } return "frog";

73 Type-checking int reptile() { } return "frog"; reptile.c: In function reptile : reptile.c:2:5: warning: return makes integer from pointer without a cast

74 Type-checking def vegetable(day): if day!= "Tuesday": return "tomato" else: return 1000

75 Type-checking def vegetable(day): if day!= "Tuesday": return "tomato" else: return 1000 Python says: no problem

76 int reptile() { } return "frog";

77 int () { } return char*;

78 int vegetable(char *day) { if (strcmp(day, "Tuesday")!= 0){ return "tomato"; } else { return 1000; } }

79 int (char*) { if (int){ return char*; } else { return int; } }

80 int (char*) { if (int){ return char*; } else { return int; } }

81 int (char*) { if (int){ return char*; } else { return int; } }

82 Everything has a single, fixed type

83 def foo(a, b): return a + b foo(2, 3) foo("2", "3")

84 Variable Declarations int foo; float foo; double foo; char foo; int foo[42]; int *foo; struct Bar foo;

85 Function Declarations double fmin(double, double); return type argument types

86 Function Declarations void exit(int); returns nothing int rand(void); takes no arguments

87 int foo(int a, int b){ } return a + b;

88 reptile.c: In function reptile : reptile.c:2:5: warning: return makes integer from pointer without a cast

89 reptile.c: In function reptile : reptile.c:2:5: warning: return makes integer from pointer without a cast int a = 4; float b = (float)a;

90 all theoretical casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

91 allowed casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

92 allowed casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

93 allowed casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

94 allowed casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

95 implicit casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

96 implicit casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

97 implicit casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

98 implicit casts int float double char int[] int* void (*f )(int) struct X int float double char int[] int* void (*f )(int) struct X

99 Compile Type-checking Linear processing

100 Linear processing ( just a small note)

101 You can only use what s declared above

102 int main() { printf("%d\n", answer()); return 0; } int answer() { } return 1337;

103 int main() { printf("%d\n", answer()); return 0; } int answer() { } return 1337;

104 int answer() { } return 1337; int main() { printf("%d\n", answer()); return 0; }

105 int answer(); declaration int main() { printf("%d\n", answer()); return 0; } int answer() { definition return 1337; }

106 HMM

107 int answer(); declaration int main() { printf("%d\n", answer()); return 0; } int answer() { definition return 1337; }

108 int answer(); declaration int main() { printf("%d\n", answer()); return 0; } int answer() { definition return 1337; }

109 int answer(); declaration #include "answer.h" int main() { printf("%d\n", answer()); return 0; } int answer() { definition return 1337; }

110 Pre-Process Compile Link

111 main.o int main() int answer()

112 main.o int main()

113 answer.c: In function main : answer.c:4: warning: implicit declaration of function answer Undefined symbols for architecture x86_64: "_answer", referenced from: _main in ccuzmrrm.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status

114 answer.c: In function main : answer.c:4: warning: implicit declaration of function answer Undefined symbols for architecture x86_64: "_answer", referenced from: _main in ccuzmrrm.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status

115 answer.c: In function main : answer.c:4: warning: implicit declaration of function answer Undefined symbols for architecture x86_64: "_answer", referenced from: _main in ccuzmrrm.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status Compiler: I don t know what answer is. I ll assume it returns an int.

116 answer.c: In function main : answer.c:4: warning: implicit declaration of function answer Undefined symbols for architecture x86_64: "_answer", referenced from: _main in ccuzmrrm.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status

117 answer.c: In function main : answer.c:4: warning: implicit declaration of function answer Undefined symbols for architecture x86_64: "_answer", referenced from: _main in ccuzmrrm.o ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status Linker: I looked in all the object files, but I couldn t find answer.

118 main.o int main()

119 main.o answer.o int main() int answer()

120 main.o answer.o int main() int answer() int main() { printf("%d\n", answer()); return 0; } int answer() { return 1337; }

121 main.o answer.o int main() int answer()

122 prog int main() int answer() gcc -o prog main.c answer.c

123 answer.c: In function main : answer.c:4: warning: implicit declaration of function answer

124 answer.c: In function main : answer.c:4: warning: implicit declaration of function answer Compiler: I don t know what answer is. I ll assume it returns an int.

125 answer.h int answer(); main.c #include "answer.h" int main() { printf("%d\n", answer()); return 0; }

126 answer.h int answer(); answer.c #include "answer.h" int answer() { } return 1337;

127 Summary

128 answer.h int answer(); main.c #include "answer.h" int main() { printf("%d\n", answer()); return 0; }

129 Preprocess: gcc -E main.c int answer(); int main() { printf("%d\n", answer()); return 0; }

130 Compile: gcc -c main.c main.c main.o answer.o

131 Link: gcc -o prog main.o main.o prog

132 Pre-Process Compile Link

133 Slides & Further Reading web.mit.edu/6.s096/

134 Registration, Wait List Stellar Grading: -,, + or better passes 70% assignments, 30% project

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