CAAM 420 Daily Note. Scriber: Qijia Jiang. Date: Oct.16. Project 3 Due Wed 23.Oct. Two parts: debug code and library exercise.

Size: px

Start display at page:

Download "CAAM 420 Daily Note. Scriber: Qijia Jiang. Date: Oct.16. Project 3 Due Wed 23.Oct. Two parts: debug code and library exercise."

Derrick Harmon
5 years ago
Views:

1 CAAM 420 Daily Note Scriber: Qijia Jiang Date: Oct.16 1 Announcement Project 3 Due Wed 23.Oct. Two parts: debug code and library exercise. 2 Make Convention Make syntax for library directories and library names: gcc... -L (directory path) -l [library name] where [library name] is lib[library name].a Here s a Makefile example for library: # a standard (pkg)/lib makefile - the variable LIB should be # defined in the main directory, and this makefile should be # invoked from there. # local include directory by default - can be augmented by # other include dirs INC = -I../include # list of source and header file dependencies - easier than # typing them one at a time SRC = cvector.c #name of library to be created - standard form LIB = libcvector.a ################ Standard rules - work for all simple examples 1

2 # list of object files OBJ = $(SRC:.c=.o) # pattern rules - in the dependency statement, % stands for # any string, the same string on both sides of the ":". In the # command (after the tab), $< is the input file (on the right # of the :), $@ is the output (on the left of the ":". To # evaluate a make variable, put it in parens and prefix a $. default: $(LIB) %.o: %.c gcc -c -Wall $< $(INC) $(LIB): $(OBJ) ar cr $(LIB) $(OBJ); ranlib $(LIB) clean: /bin/rm -f *.o *~ burn: clean /bin/rm -f *.a A note about relative path name: Relative path name is relative to the path they ll be used. Absolute path, however, can change from machine platform to machine platform (example: grep). 3 Example of Really Bad Code 1 #include <s t d i o. h> #include <s t d l i b. h> 3 5 void v e c t o r a d d s q u a r e ( int N, int pt a, int pt b, int p t c ){ / add two v e c t o r s and square the r e s u l t / 7 int i ; 9 for ( i =0; i<=n; i++) p t c [ i ] = pt a [ i ] + pt b [ i ] ; 11 p t c [ i ] = p t c [ i ] p t c [ i ] ; 2

3 13 / f r e e up arrays t h a t are no l o n g e r needed to avoid memory l e a k / 15 f r e e ( pt a ) ; f r e e ( pt b ) ; / to run the code :. / main 10 / int main ( int argc, char argv ){ 21 / read the f i r s t command l i n e argument, remembering C i s 23 0 indexed / int N = a t o i ( argv [ 0 ] ) ; 25 int i, j ; 27 / a l l o c a e t t h r e e arrays. N d o u b l e s per array. / double pt a = ( double ) malloc (N) ; 29 double pt b = ( double ) malloc (N) ; double p t c = ( double ) malloc (N) ; 31 / s e t a and b / 33 for ( i =0;( i++)<n; ) // neat o p t i m i z a t i o n of bound check pt a [ i ] = i ; 35 pt b [ i ] = i ; 37 // c a l l f u n c t i o n to add a and b and square the r e s u l t v e c t o r a d d s q u a r e (N, pt a, pt b, p t c ) ; 39 // p r i n t out r e s u l t s 41 for ( i =0; i<n;++ i ){ p r i n t f ( p t c [%d ] = %l f \n, p t c [ i ] ) ; // t i d y up f r e e ( pt a ) ; 47 f r e e ( pt b ) ; f r e e ( p t c ) ; 49 This example code takes two vectors, add them up entry by entry, and squares the entries. One problem is the scope of for statement. Example: #include "cstd.h" int main(){ 3

4 int i; int j; for (i=0; i<10; i++) j = i*i; printf("%d\n",j); Without the curly braces around the for loop, the result in this case will be 81 i will have the last value in the loop, instead of 0,1,4, C++ basic features C++ is almost a subset of C. One exception is that it lacks the long long type in C. g++ is the GNU C++ compiler. Improvements compared to C: Boolean Type bool x = true; #include "cstd.h" int main(){ int i; bool j; for (i=0; i<10; i++){ if (i==0) j = false; else j = true; j = j*j; printf("%d\n",j); Output : a vector with 0 for its first element and 1 for the rest Pass by Reference - alternative to pass by value: double x = 1.0; double &y = x; // reference to x, y = another name for x y = y+1.0; // x = x+1; C pass by value: 4

5 double x =... void foo (double *x){ *x = (*x)*(*x); C++ pass by reference: double x =... // create a reference to x as part of function call void foo (double &x){ x = x*x; // inside, x is a reference to x outside Note: References must be initialized! double x = 1.0; double &y; // error double &z = x; // okay References can t be declared on their own without assignment. double &p; foo(p); // compiler-level error But it would be right if written like this: double p = 1.0; foo(p); Better Dynamic Memory: - new = malloc - delete = free C: float *x = (float *) malloc (sizeof(float)*10); free(x); C++: float *x = new float[10] delete [ ] x; // array length Easy to define full-fledged types. 5

Common Misunderstandings from Exam 1 Material

Common Misunderstandings from Exam 1 Material Kyle Dewey Stack and Heap Allocation with Pointers char c = c ; char* p1 = malloc(sizeof(char)); char** p2 = &p1; Where is c allocated? Where is p1 itself