INTRODUCTION. This is not a full c-programming course. It is not even a full 'Java to c' programming course.

Transcription

1 C PROGRAMMING 1

2 INTRODUCTION This is not a full c-programming course. It is not even a full 'Java to c' programming course. 2

3 LITTERATURE 3. 1

4 FOR C-PROGRAMMING The C Programming Language (Kernighan and Richie) - The bible, and the book that is referenced in this material. Essential C Online c-course Another online c-course Yet another online c-course

5 FOR VALGRIND Quickstart guide User manual 3. 23

6 FOR MAKEFILE AND DDD Tutorial for makefile Manual for ddd debugger 3. 4

7 GETTING STARTED 4. 1

8 HELLO WORLD hello_world.c # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { p r i n t f ( " H e l l o w o r l d! \ n " ) ; r e t u r n 0 ; } gcc hello_world.c./a.out Compile using: which will generate a.out Run using:

9 COMPILER FLAGS You can (and are recommended to) compile with several flags to the compiler: -g = debug information -Wall = All warnings are displayed -O9 = Optimization gcc -g -Wall hello_world.c Which makes it: 4. 2

10 VARIABLE TYPES char int float double short/long can specify size. signed (use 1 bit for sign)/unsigned const int i = 42; i is not a variable. 4. 3

11 STATIC VARIABLES You can declare a variable static, and if done in global scope, use it inside functions etc. # i n c l u d e < s t d i o. h > s t a t i c i n t i = 0 ; i n t m a i n ( v o i d ) { p r i n t f ( " % i \ n ", i ) ; i = i + 1 ; p r i n t f ( " % i \ n ", i ) ; r e t u r n 0 ; } 4. 4

12 GLOBAL VARIABLES Prefixing variables with extern makes them globally visible from other files

13 STRINGS AND ARRAYS Strings are arrays of char Hello" is the same as char str[] = {'H','e','l','l','o','\0'} We will cover much more on strings when we get to pointers. # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { c h a r s t r [ ] = { ' H ', ' e ', ' l ', ' l ', ' o ', ' \ 0 ' } ; p r i n t f ( " % s - % s \ n ", s t r, " H e l l o " ) ; r e t u r n 0 ; }

14 ENUMS # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { e n u m f i r s t m o n t h s { J A N, F E B, M A R, A P R } ; e n u m l a s t m o n t h s { N O V = 1 0, D E C = 1 1 } ; p r i n t f ( " % i \ n ", J A N ) ; p r i n t f ( " % i \ n ", N O V ) ; r e t u r n 0 ; } All enumerated values must be different, and will start with 0 if not explicitly defined. 4. 7

15 OPERATORS + - * / % 4. 89

16 COMPARISON: < <= > >= ==!= 4. 10

17 LOGIC 0 is false, everything else is true! is used for negation &&is boolean AND is boolean OR

18 BITWISE OPERATORS & is bitwise AND is bitwise OR ^ is bitwise XOR << is left shift 4. 11

19 BITWISE OPERATORS # i n c l u d e < s t d i o. h > s t a t i c u n s i g n e d i n t b i n a r y = 6 ; s t a t i c u n s i g n e d i n t b i n a r y = 2 ; i n t m a i n ( v o i d ) { p r i n t f ( " % i \ n ", b i n a r y & b i n a r y ) ; p r i n t f ( " % i \ n ", b i n a r y b i n a r y ) ; p r i n t f ( " % i \ n ", b i n a r y ^ b i n a r y ) ; p r i n t f ( " % i \ n ", b i n a r y < < 1 ) ; p r i n t f ( " % i \ n ", b i n a r y > > 1 ) ; r e t u r n 0 ; } 4. 12

20 PRINTF Arguments % int/decimal numner %uunsigned number %csingle character %sprints a string %ppointer address 4. 13

21 PRINTF There are more arguments to specify adjustment and width, check the book/manual. If you create a segfault, and you do not use \n with your printf, you are not guaranteed that it is printed!

22 INCREMENT/DECREMENT ++and --can be used both before and after an operator. i++ ++i Increments i after its value is used Increments i before its value is used

23 INCREMENT/DECREMENT # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { i n t i, j, b e f o r e, a f t e r ; i = 0 ; j = 0 ; b e f o r e = + + i ; a f t e r = j + + ; } p r i n t f ( " B : % i A : % i i : % i, j : % i \ n ", b e f o r e, a f t e r, i, j ) ; r e t u r n 0 ; 4. 16

24 CONTROL FLOW Looks like java/python etc

25 LOOPS # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { i n t i ; f o r ( i = 0 ; i < 1 0 ; i + + ) { p r i n t f ( " i : % i \ n ", i ) ; } i = 0 ; w h i l e ( i < 1 0 ) { p r i n t f ( " i : % i \ n ", i ) ; i + + ; }

26 IF/ELSE # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { i n t i ; i = 1 ; i f ( i ) { p r i n t f ( " i f s t a t e m e n t \ n " ) ; } e l s e { p r i n t f ( " e l s e s t a t e m e n t \ n " ) ; } } r e t u r n 0 ; 5. 2

27 SWITCH # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { i n t i ; s w i t c h ( i ) { c a s e 0 : p r i n t f ( " i i s 0 \ n " ) ; b r e a k ; c a s e 1 : p r i n t f ( " i i s 1 \ n " ) ; b r e a k ; d e f a u l t : p r i n t f ( " i i s n o t 0 o r 1 \ n " ) ; b r e a k ; } r e t u r n 0 ; } 5. 3

28 BREAK break can be used in both loops and switches to exit them. continue can only be used in loops, and jumps to the beginning of the loop

29 STYLE COMMENTS A nice c-style guide can be found at Declare all variables of a function before anything else. Including before you assign them any value 5. 6

30 FUNCTIONS, STRUCTS, ETC. 6. 1

31 FUNCTIONS Remember to forward declare functions. If you use a function before it is declared, it is an error. # i n c l u d e < s t d i o. h > / / T h e a d d m e t h o d i s f o r w a r d d e c l a r e d, b e c a u s e i t i s u s e d b e f o r e i t i i n t a d d ( i n t a, i n t b ) ; i n t m a i n ( v o i d ) { i n t i, j ; i = 2 ; j = 3 ; p r i n t f ( " i + j f u n c t i o n s t y l e = % i \ n ", a d d ( i, j ) ) ; r e t u r n 0 ; } i n t a d d ( i n t a, i n t b ) { r e t u r n a + b ; }

32 # i n c l u d e < s t d i o. h > RECURSIVE FUNCTIONS i n t f a c t o r i a l ( i n t i ) ; Notice again the forward declaration i n t m a i n ( v o i d ) { p r i n t f ( " 5! = % i \ n ", f a c t o r i a l ( 5 ) ) ; r e t u r n 0 ; } i n t f a c t o r i a l ( i n t i ) { i f ( i = = 0 ) { r e t u r n 1 ; } r e t u r n i * f a c t o r i a l ( i - 1 ) ; } 6. 2

33 HEADER FILES/INCLUDING OTHER FILES To divide code into logical parts, you can split it across multiple (pair of) files. The function declarations, defined variables, structs etc. (think the public stuff), is declared in a header file, ending with.h. The implementation is kept in a code file, ending with.c 6. 3

34 INCLUDING HEADER FILES Both user and system header files are included using the preprocessing directive `#include `. It has following two forms: #include <file> This form is used for system header files. It searches for a file named file in a standard list of system directories. You can prepend directories to this list with the -I option while compiling your source code. #include "file" This form is used for header files of your own program. It searches for a file named file in the directory containing the current file. You can prepend directories to this list with the

35 I option while compiling your source code. ONCE-ONLY HEADERS If a header file happens to be included twice, the compiler will process its contents twice and will result an error. The standard way to prevent this is to enclose the entire real contents of the file in a conditional, like this: # i f n d e f H E A D E R _ F I L E # d e f i n e H E A D E R _ F I L E t h e e n t i r e h e a d e r f i l e f i l e # e n d i f This construct is commonly known as a wrapper #ifndef. When the header is included again, the conditional will be false, because HEADER_FILEis defined. The preprocessor will skip over the entire contents of the 6. 5

36 file, and the compiler will not see it twice.

37 STRUCTS A Struct is a group of variables, that belong togeather in a logical way. # i n c l u d e < s t d i o. h > s t r u c t A c c o u n t { d o u b l e a m o u n t ; i n t a c c o u n t _ i d ; } ; i n t m a i n ( v o i d ) { s t r u c t A c c o u n t a c c o u n t ; a c c o u n t. a c c o u n t _ i d = ; a c c o u n t. a m o u n t = ; p r i n t f ( " A c c i d % i a m o u n t : % g \ n ", a c c o u n t. a c c o u n t _ i d, a c c o u n t. a m o u / / U g l y s h o r t c u t - o r d e r i n g m a t t e r s. s t r u c t A c c o u n t a c c o u n t 2 = { , } ; p r i n t f ( " A c c. i d % i a m o u n t : % g \ n ", a c c o u n t 2. a c c o u n t _ i d, a c c o u n t 2. a 6. 6

38 TYPEDEF To avoid typing struct a lot of times, it is common to use typedef # i n c l u d e < s t d i o. h > t y p e d e f s t r u c t _ a c c o u n t { d o u b l e a m o u n t ; i n t a c c o u n t _ i d ; } a c c o u n t ; i n t m a i n ( v o i d ) { a c c o u n t a c c ; a c c. a c c o u n t _ i d = ; a c c. a m o u n t = ; } p r i n t f ( " A c c o u n t i d % i a m o u n t : % g \ n ", a c c. a c c o u n t _ i d, a c c. a m o u n t ) ; r e t u r n 0 ; 6. 7

39 UNION In datastructures etc. you sometimes need to use one or another set of variables. A union only uses space like the biggest of the sets # i n c l u d e < s t d i o. h > u n i o n C a r d { / * P l a y i n g c a r d * / i n t v a l u e ; c h a r f a c e [ 8 ] ; / / T r y u s i n g 9 - e x p l a i n } ; i n t m a i n ( v o i d ) { u n i o n C a r d c a r d 1 ; u n i o n C a r d c a r d 2 ; c a r d 1. v a l u e = 5 ; c a r d 2. f a c e [ 0 ] = ' Q ' ; c a r d 2. f a c e [ 1 ] = ' u ' ; c a r d 2. f a c e [ 2 ] = ' e ' ; c a r d 2. f a c e [ 3 ] = ' e ' ; c a r d 2. f a c e [ 4 ] = ' n ' ; c a r d 2. f a c e [ 5 ] = ' \ 0 ' ; p r i n t f ( " C a r d 1 : % i C a r d 2 % s \ n ", c a r d 1. v a l u e, c a r d 2. f a c e ) ; p r i n t f ( " M e m : % l i = % l i \ n ", s i z e o f ( c a r d 1 ), s i z e o f ( c a r d 2 ) ) ; p r i n t f ( " C a r d 1 : % s C a r d 2 % i \ n ", c a r d 1. f a c e, c a r d 2. v a l u e ) ; r e t u r n 0 ; } 6. 8

40 DEFINES Defines are inserted before the code is compiled. # i n c l u d e < s t d i o. h > # d e f i n e V A L U E 4 2 # d e f i n e D I V ( a, b ) ( a ) / ( b ) i n t m a i n ( v o i d ) { p r i n t f ( " V a l u e : % i \ n ", V A L U E ) ; p r i n t f ( " D I V ( 6, 3 ) : % i \ n ", D I V ( 6, 3 ) ) ; } r e t u r n 0 ; 6. 9

41 POINTERS AND ARRAYS

42 POINTERS Every variable is located somewhere in memory, and thus have an adress where it is located. A pointer is a variable, that is an adress of another variable. A pointer is defined with a star in from of the variable name: int *pointer; You can declare more pointers on the same line, but the star must be with each variable: int *pointer, *also_pointer; To get the adress of a variable, you can use the & operator

43 POINTERS The following example is commented for the operators used with pointers # i n c l u d e < s t d i o. h > i n t m a i n ( v o i d ) { i n t x = 4 2 ; / * A n o r m a l i n t e g e r * / i n t * p ; / * A p o i n t e r t o a n i n t e g e r ( " * p " i s i n t e g e r, s o p m u s t b e a p o i n t e r t o a n i n t e g e r ) * / p = & x ; / * A s s i g n t h e a d d r e s s o f x t o p * / p r i n t f ( " x h a s v a l u e % i \ n ", x ) ; p r i n t f ( " I t s a d d r e s s i s % p \ n ", p ) ; } / * N o t e t h e u s e o f t h e * t o g e t t h e v a l u e * / p r i n t f ( " U s i n g p o i n t e r i, t h e v a l u e o f x : % i \ n ", * p ) ; r e t u r n 0 ; 7. 2

44 POINTERS In this example, the value of i is changed by change() even through it does not have i in its scope # i n c l u d e < s t d i o. h > v o i d c h a n g e ( i n t * p o i n t e r ) { * p o i n t e r = 4 2 ; } i n t m a i n ( v o i d ) { i n t i = 2 ; c h a n g e ( & i ) ; p r i n t f ( " i : % i \ n ", i ) ; r e t u r n 0 ; } 7. 3

45 POINTERS WITH STRUCTS The arrow: is a shorthand notation, for retrieving values from a struct pointer # i n c l u d e < s t d i o. h > # i n c l u d e < s t d l i b. h > t y p e d e f s t r u c t _ A c c o u n t { d o u b l e a m o u n t ; i n t a c c o u n t _ i d ; } A c c o u n t ; i n t m a i n ( v o i d ) { A c c o u n t a c c o u n t ; A c c o u n t * a c c P o i n t e r ; a c c o u n t. a c c o u n t _ i d = ; a c c o u n t. a m o u n t = ; a c c P o i n t e r = & a c c o u n t ; p r i n t f ( " a m o u n t : % g \ n ", ( * a c c P o i n t e r ). a m o u n t ) ; p r i n t f ( " a m o u n t : % g \ n ", a c c P o i n t e r - > a m o u n t ) ; r e t u r n E X I T _ S U C C E S S ; } 7. 4

46 ARRAYS REVISITED Arrays are just pointers to its first element! The following is therefore equivalent Array access arr[0] Table 1. Table title Pointer access *arr arr[2] *(arr + 2) arr[n] *(arr + n) 7. 5

47 MEMORY HANDLING AND I/O

48 MEMORY HANDLING Local variables are placed in the Stack part of memory, and are only valid in the scope of the method. Once a method has returned, the memory is no longer available for that variable. For more permanent location, memory must be allocated on the heap. For this you can use the void *malloc(int num);function. It allocates an array of num bytes and leave them initialized. When the memory is no longer needed, you can use free() to hand it back to the operating system.

49 MEMORY HANDLING (1) # i n c l u d e < s t d i o. h > # i n c l u d e < s t d l i b. h > # i n c l u d e < s t r i n g. h > i n t m a i n ( v o i d ) { c h a r s t r i n g 1 [ ] ; c h a r * s t r i n g 2 ; ( 1 ) } r e t u r n E X I T _ S U C C E S S ; 1 See next slide 8. 2

50 MEMORY HANDLING (1) / / U s i n g a s t r i n g c o p y f u n c t i o n s t r c p y ( s t r i n g 1, " I ' m a n a r r a y, m e m o r y o n s t a c k " ) ; / * a l l o c a t e m e m o r y d y n a m i c a l l y * / s t r i n g 2 = m a l l o c ( * s i z e o f ( c h a r ) ) ; / / I f m a l l o c r e t u r n s N U L L, s o m e t h i n g w e n t w r o n g ( o u t o f m e m o r y ) i f ( s t r i n g 2 = = N U L L ) { / / f p r i n t f : O u t p u t w r i t t e n t o s t r e a m, h e r e : s t d e r r o r f p r i n t f ( s t d e r r, " E r r o r : u n a b l e t o a l l o c a t e r e q u i r e d m e m o r y \ n " ) ; } e l s e { s t r c p y ( s t r i n g 2, " I ' m n o w s t o r i n g d a t a o n t h e h e a p " ) ; } p r i n t f ( " s t r i n g 1 = % s \ n ", s t r i n g 1 ) ; p r i n t f ( " s t r i n g 2 = % s \ n ", s t r i n g 2 ) ; / / I ' m d o n e u s i n g t h e m e m o r y - h a n d i t b a c k n i c e l y f r e e ( s t r i n g 2 ) ; 8. 3

51 READING/WRITING FILES C communicates with files using a new datatype called a file pointer. This type is defined within stdio.h, and written as FILE *. A file pointer called input_file is declared in a statement like FILE *input_file; 8. 4

52 READING/WRITING FILES To open aa file, you use fopen(filename, mode). The mode can be one of the following: ropen file for reading wopen file for writing aopen file for appending You close a file using fclose(file);. There is a limit of open files on a system, and it is bad style to not close a file after use. 8. 5

53 READING FILES To read and write input, there are various methods, but an easy one for reading is: char *fgets( char *buf, int n, FILE *fp ); The functions fgets()reads up to n-1 characters from the input stream referenced by fp. It copies the read string into the buffer buf, appending a null character to terminate the string. If this function encounters a newline character '\n' or the end of the file EOF before they have read the maximum number of characters, then it returns only the characters read up to that point including new line character. 8. 6

54 READING FILES Notice that stdin, stdout, stderr all are filepointers, but they are always open, and do not need to be opened with fopen

55 WRITING FILES For writing, the equivalent is: int fputs( const char *s, FILE *fp ); The function fputs()writes the string s to the output stream referenced by fp. It returns a non-negative value on success, otherwise EOF is returned in case of any error.

56 WRITING FILES # i n c l u d e < s t d i o. h > # i n c l u d e < s t d l i b. h > # i n c l u d e < s t r i n g. h > i n t f i l e _ c o p y ( c h a r * f i l e n a m e _ i n, c h a r * f i l e n a m e _ o u t ) ; i n t m a i n ( v o i d ) { r e t u r n f i l e _ c o p y ( ". / t e s t. t x t ", ". / c o p i e d. t x t " ) ; } i n t f i l e _ c o p y ( c h a r * f i l e n a m e _ i n, c h a r * f i l e n a m e _ o u t ) { F I L E * i n f i l e ; F I L E * o u t f i l e ; c h a r l i n e [ ] ; ( 1 ) ( 2 ) r e t u r n E X I T _ S U C C E S S ; } 1 See next slide 2 See the following slide 8. 9

57 WRITING FILES i n f i l e = f o p e n ( f i l e n a m e _ i n, " r " ) ; i f (! i n f i l e ) { f p r i n t f ( s t d e r r, " C o u l d n o t o p e n i n p u t f i l e " ) ; r e t u r n E X I T _ F A I L U R E ; } o u t f i l e = f o p e n ( f i l e n a m e _ o u t, " w " ) ; i f (! o u t f i l e ) { f c l o s e ( i n f i l e ) ; f p r i n t f ( s t d e r r, " C o u l d n o t o p e n o u t p u t f i l e " ) ; r e t u r n E X I T _ F A I L U R E ; } 8. 10

58 WRITING FILES w h i l e ( f g e t s ( l i n e, 2 5 6, i n f i l e ) ) { p r i n t f ( " C o p y i n g t h e l i n e : ' % s ' ", l i n e ) ; f p u t s ( l i n e, o u t f i l e ) ; } f c l o s e ( i n f i l e ) ; f c l o s e ( o u t f i l e ) ; If you prefer to read one char at a time, fgetcand fputc can be used 8. 11

59 SORTING AN ARRAY The build in function qsortcan be used for this. # i n c l u d e < s t d i o. h > # i n c l u d e < s t d l i b. h > e n u m s u i t s { D I A M O N D S, H E A R T S, S P A D E S, C L U B S } ; t y p e d e f s t r u c t _ C a r d { / * P l a y i n g c a r d * / i n t v a l u e ; i n t s u i t ; } C a r d ; c h a r * g e t S u i t ( i n t s u i t ) { s w i t c h ( s u i t ) { c a s e D I A M O N D S : r e t u r n " D i a m o n d s " ; c a s e H E A R T S : r e t u r n " H e a r t s " ; c a s e C L U B S : r e t u r n " C l u b s " ; c a s e S P A D E S : r e t u r n " S p a d e s " ; } r e t u r n N U L L ; } 1 See following slides 8. 12

60 SORTING AN ARRAY Make a comparator function i n t c o m p a r e C a r d s ( C a r d * * c 1, C a r d * * c 2 ) { i f ( ( * c 1 ) - > v a l u e = = ( * c 2 ) - > v a l u e ) { r e t u r n ( * c 1 ) - > s u i t - ( * c 2 ) - > s u i t ; } r e t u r n ( * c 1 ) - > v a l u e - ( * c 2 ) - > v a l u e ; }

61 SORTING AN ARRAY i n t m a i n ( v o i d ) { i n t i, j ; C a r d * d e c k [ 5 2 ] ; } / / F i l l a r r a y w i t h d e c k o f c a r d s f o r ( i = 0 ; i < 4 ; i + + ) { f o r ( j = 0 ; j < 1 3 ; j + + ) { d e c k [ i * j ] = m a l l o c ( s i z e o f ( C a r d ) ) ; d e c k [ i * j ] - > v a l u e = 1 + j ; d e c k [ i * j ] - > s u i t = i ; } } ( 1 ) r e t u r n 0 ;

62 SORTING AN ARRAY / / P r i n t a l l c a r d s f o r ( i = 0 ; i < 5 2 ; i + + ) { p r i n t f ( " S u i t : % s, v a l u e : % i \ n ", g e t S u i t ( d e c k [ i ] - > s u i t ), d e c k [ i ] - > } / / W i s h s o r t e d b y ( v a l u e, d e c k ) p r i n t f ( " \ n S o r t i n g! \ n \ n " ) ; q s o r t ( d e c k, 5 2, s i z e o f ( C a r d * ), ( i n t ( * ) ( c o n s t v o i d *, c o n s t v o i d * ) ) / / P r i n t a l l c a r d s f o r ( i = 0 ; i < 5 2 ; i + + ) { p r i n t f ( " S u i t : % s, v a l u e : % i \ n ", g e t S u i t ( d e c k [ i ] - > s u i t ), d e c k [ i ] - > } 8. 15

63 MAKEFILE

64 MAKEFILE WHY? Checks timestamps to see what has changed and rebuilds just what you need, without wasting time rebuilding other files. Manage Several source files and compile them quickly with a single Command Line. Make layers a rich collection of options that lets you manipulate multiple directories, build different versions of programs for different platforms, and customize your builds in other ways.

65 MAKE UTILITY If you run make This will cause the make program to read the Makefile and build the first target it finds there. If you have several makefiles, then you can execute them with the command: make -f mymakefile For more options use: man make 9. 2

66 HOW DOES IT WORK? Typically the default goal in most makefiles is to build a program. This usually involves many steps: 1. Generate the source code using some utilities like Flex & Bison. 2. Compile the source code into binary file (.o files c/c++/java etc.) 3. bound the Object files together using a linker( gcc/g++) to form an executable program 9. 3

67 MAKEFILE STRUCTURE Makefiles contain definitions and rules. A definition has the form: VAR=value A rule has the form: output files: input files commands to turn inputs to outputs All commands must be tab-indented. To reference the variable VAR, surround it with $(VAR). 9. 4

68 RULES Makefile contains a set of rules used to build an application. The first rule (default rule) seen by make consists of three parts: 1. The Target. 2. The Dependencies. 3. The Command to be performed. 9. 5

69 HOW TO MAKE A SIMPLE MAKEFILE Here s a simple example for a C program that defines foo() in foo.c, but uses it in bar.c. C C = g c c b a r : b a r. c f o o. h f o o. o $ ( C C ) - o b a r b a r. c f o o. o f o o. o : f o o. c f o o. h $ ( C C ) - c f o o. c r u n : c l e a n :. / b a r r m - f b a r f o o. o 9. 6

70 CONVENTIONS It s common to include pseudo-targets in makefiles to automate other parts of the development process. make clean The rule for clean in the previous example doesn t build a file called clean. Rather, it deletes all of the build targets to allow a fresh build from scratch. Including a clean rule is a common convention for make. make test Running make test often runs the test suite for the software. make install Running make install typically installs the compiled binary in a PATH-accessible location. 9. 7

71 For software using the autoconf toolchain, the installation directory is set by running./configure command prior to using make. make run For simple programs, make run acts like an alias to the compiled binary.

72 VALGRIND

73 VALGRIND The Valgrind tool suite provides a number of debugging and profiling tools that help you make your programs faster and more correct. The most popular of these tools is called Memcheck. It can detect many memory-related errors that are common in C and C++ programs and that can lead to crashes and unpredictable behaviour.

74 PREPARTION Compile your program with -gto include debugging information so that Memcheck s error messages include exact line numbers. Using -O0is also a good idea With -O1line numbers in error messages can be inaccurate Use of -O2and above is not recommended as Memcheck occasionally reports uninitialised-value errors which don t really exist

75 RUNNING MEMCHECK If you normally run your program like this:./myprog arg1 arg2 Use this command line: valgrind --leak-check=yes./myprog arg1 arg2 Memcheck is the default tool. The --leak-check option turns on the detailed memory leak detector

76 CAVEATS Memcheck is not perfect; it occasionally produces false positives

77 DEBUGGING - DDD 11. 1

78 DEBUGGING - DDD DDD is a graphical front-end for GDB and other commandline debuggers

79 DDD Run from command line ddd Must compile programs with -gflag to get debug information included 11. 3

80 USAGE Step through a program Use breakpoints See values of viariables 11. 4

81 QUESTIONS 12