Problems 5
  1. Theory
    1. What is EOF in the context of fscanf? Hints: 
      man scanf | grep -A 1 -B 4 EOF
      and wikipedia article end of file.
    2. What is the meaning of the following makefile variables: CC, CFLAGS, CXXFLAGS, CPPFLAGS, LDFLAGS, LDLIBS.
      Hint: make's implicit variables and implicit rules.
    3. What will the following makefile print (after running command make) 
      CFLAGS = -Wall -Ofast -std=c1x
C = F
all:
	echo CFLAGS
	echo $CFLAGS
	echo $(C)FLAGS
	echo $(CFLAGS)

    4. Suppose you have your whole C-program in one file main.c. Which of the following makefiles will compile and link the program into the executable file main? 

      1. all: main

      2. main: main.c

      3. main: main.o

      4. all: main
main: main.o
main.o: main.c

      5. all: main
main.o: main.c
main: main.o

      6. main.o: main.c
all: main
main: main.o

      7. main: main.c
	cc main.c -o main

      8. main: main.c
	$(CC) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@

      9. all: main
main: main.o
	cc main.o -o main
main.o: main.c
	cc -c main.c -o main.o
      Remember that the tabulator-sign before the command may not be copy-pasted correctly.

    5. Suppose your main function, contained in the file main.c, calls the functions foo and bar which are contained correspondingly in the files foo.c and bar.c. Which of the following makefiles will correctly compile and link your program into the executable file main after the command make? 

      1. main: main.o foo.o bar.o

      2. main: foo.o main.o bar.o

      3. main: foo.o main.o bar.o
	cc foo.o main.o bar.o -o main

      4. main: main.o foo.o bar.o
	$(CC) $(LDFLAGS) $^ $(LDLIBS) -o $@

      5. main: main.o foo.o bar.o
main.o: main.c
foo.o: foo.c
	cc -c $^ -o $@
bar.o: bar.c

      6. main: main.o foo.o bar.o
	cc main.o foo.o bar.o -lm -o main
main.o: main.c
	cc -c main.c
foo.o: foo.c
	cc -c foo.c
bar.o: bar.c
	cc -c bar.c

      7. obj = main.o foo.o bar.o
main: $(obj)
    6. Suppose there is the following preprocessor directive at the beginning of the file, 
      #define PI 3.1415927
      what is the effect of it?
      1. The compiler creates a variable PI of type double and stores the value 3.1415927 in it.
      2. All occurences of the token 'PI' in the file are substituted with the token '3.1415927'.
  2. Practice. These exercises should be done using the make untility and Makefile(s).
    1. Build a program that reads a set of numbers from the file input.dat and writes the numbers together with their cosines in a table form to the file output.dat. Hint: 
      double x;
FILE* in = fopen("input.dat","r");
if(in == NULL){ fprintf(stderr,"error: could not open file\n"); return -1;}
FILE* out = fopen("output.dat","w");
while( fscanf(in,"%lg",&x) != EOF ) fprintf(out,"%lg \t %lg\n",x,cos(x));
      makefile ($@ stands for the name of the target): 
      CFLAGS = -Wall -std=c99
LDLIBS = -lm
output.dat: file_io input.dat ; ./file_io
input.dat: makefile ; echo '1.0 1.1 1.2 1.3 1.4' > input.dat
clean: ; $(RM) input.dat output.dat file_io
    2. Do the same, but now using standard input, standard output and redirections. Hint: 
      while( fscanf(stdin,"%lg",&x) != EOF ) fprintf(stdout,"%lg \t %lg\n",x,cos(x));
      or even shorter, 
      while( scanf("%lg\n",&x) != EOF ) printf("%lg \t %lg\n",x,cos(x));
      In the makefile: 
      std_io.out.txt: std_io input.dat; ./std_io < input.dat > std_io.out.txt
    3. Do the same, but now the input should be done via command-line-arguments. Hints: 
      for(int i=1; i<argc; i++){double x=atof(argv[i]); printf("%lg\t%lg\n",x,cos(x));}
      In the makefile (the automatic variable $@ stands for the name of the target of the rule): 
      cmd_io.out.txt: cmd_io makefile ; ./cmd_io 1.0 1.1 1.2 1.3 > $@
    4. Similar to tri_vectors from Problems-3 and my_matrices from Problems-4 implement arbitrary-length vectors using the structure typedef struct {int size; double* data;} vector; with the following functions: 
      vector* vector_alloc(int size);
void vector_free(vector* v);
void vector_set(vector* v, int i, double x); /* v_i=x */
double vector_get(vector* v, int i); /* returns v_i */
double* vector_get_ptr(vector* v, int i); /* returns pointer to v_i */
void vector_set_all(vector* v, double x); /* for every i v_i=x */
int vector_fprintf(FILE* stream, const char* format, vector* v);
	/* prints the elements of v to the specified stream using the specified
	format; returns 0 for success, -1 otherwise */
int vector_fscanf(FILE* stream, const char* format, vector* v);
	/* reads (*v).size elements form the stream into the vector v;
	returns 0 for success, -1 otherwise */
void vector_add(vector* v, vector* u);
void vector_subtract(vector* v, vector* u);
void vector_scale(vector* v, double a);
int vector_equal(const vector* v, const vector* u);
      Use assert.h for range checking.