Lab 1: C for C++ programmers

1. Use printf() instead of cout and fprintf(stderr, "...") instead of cerr. eg:

   #include <stdio.h>
   
   int main(void) {
       int i = 123;
       float f = 1 / 3.0;
       double d = 1 / 3.0;
       char *str = "Hello World!";
   
       printf("i = %d, f = %.20f, d = %.20f\n"
   	   "str = %s, partial_str = %.5s\n",
   	   i, f, d, str, str);
   
      /*
       * Result:
       * i = 123, f = 0.33333334326744079590, d = 0.33333333333333331483
       * str = Hello World!, partial_str = Hello
       */
   
      return (0);
   }
       

2. Use scanf() instead of cin. eg:

   #include <stdio.h>
   
   int main(void) {
       double x, y;
   
       scanf("%lf %lf", &x, &y);
       printf("x = %f, y = %f\n", x, y);
   
       return (0);
   }
   
   Another example:
   ----------------
   #include <stdio.h>
   
   int main(void) {
       char name[32];
   
       printf("What's your name? ");
       scanf("%31[^\n]", name);
       printf("Hello, %s\n", name);
   
       return (0);
   }
       

3. Use struct instead of class. eg:

   #include <stdio.h>
   
   typedef struct {
       int x, y;
   } point_t;
   
   int main(void) {
       point_t point;
       point.x = 10;
       point.y = 20;
   
       printf("x = %d, y = %d\n", point.x, point.y);
   
       /*
        * Result:
        * x = 10, y = 20
        */
   
       return (0);
   }
       

4. Use pointer instead of reference. eg.

   #include <stdio.h>
   
   void func(int *x) {
       *x = 10;
   }
   
   int main(void) {
       int x = 0;
   
       printf("Before, x = %d\n", x);
       func(&x);
       printf("After, x = %d\n", x);
   
       /*
        * Result:
        * Before, x = 0
        * After, x = 10
        */
   
       return (0);
   }
   

5. Use malloc() and free() instead of new and delete. eg:

   #include <stdio.h>
   #include <stdlib.h>
   
   #define N    100
   
   typedef struct {
       int x, y;
   } point_t;
   
   int main(void) {
       point_t *points = (point_t *)malloc(sizeof(point_t) * N);
   
       int i;
       for (i = 0; i < N; i++) {
   	points[i].x = points[i].y = 0;
       }
   
       /* Or, we can do: memset(points, 0, sizeof(point_t) * N); */
   
       /* Blah blah blah */
   
       free(points);
   
       return (0);
   }
       

6. Use open(), close(), read(), write(), lseek() instead of fstream. eg:

   #include <stdio.h>
   #include <fcntl.h>
   #include <errno.h>
   #include <unistd.h>
   #include <string.h>
   
   #define PASSWD_FILE    "/etc/passwd"
   
   int main(void) {
       char buf[256];
       int byte_read = 0;
       int fd = open(PASSWD_FILE, O_RDONLY);
   
       if (fd < 0) {
   	fprintf(stderr,
   		"Failed to open %s: %s\n", PASSWD_FILE, strerror(errno));
   	return (1);
       }
   
       while ((byte_read = read(fd, buf, sizeof(buf))) > 0) {
   	printf("%.*s", byte_read, buf);
       }
   
       do {
   	/* Go to beginning of the file */
   	if (lseek(fd, 0, SEEK_SET) < 0) {
   	    fprintf(stderr, "Failed to call lseek(): %s\n", strerror(errno));
   	    break;
   	}
   
   	/* Advance 10 bytes from current offset */
   	if (lseek(fd, 10, SEEK_CUR) < 0) {
   	    fprintf(stderr, "Failed to call lseek(): %s\n", strerror(errno));
   	    break;
   	}
   
   	/* Go to the end of the file */
   	if (lseek(fd, 0, SEEK_END) < 0) {	
   	    fprintf(stderr, "Failed to call lseek(): %s\n", strerror(errno));
   	    break;
   	}
   
   	/* Go to 16 bytes from the end of the file */
   	if (lseek(fd, -16, SEEK_END) < 0) {
   	    fprintf(stderr, "Failed to call lseek(): %s\n", strerror(errno));
   	    break;
   	}
       } while (0);
   
       if (close(fd) < 0) {
   	fprintf(stderr,
   		"Failed to close %s: %s\n", PASSWD_FILE, strerror(errno));
       }
   
       return (0);
   }
       

7. Man page is your friend. eg:

   % man 2 mkdir
     eg. mkdir("foo", 0644) will create a directory named "foo" with permission -rw-r--r--
   % man 2 chdir
     eg. chdir("foo") will change current directory to "foo"
   % man 2 open
     eg. open("bar", O_CREAT | O_WRONLY) will create a file named "bar" for writing
   % man 2 write
     eg. write(fd, "Hello World!\n", 13) will write "Hello World!\n" into a file referenced by the file descriptor fd 
   % man 2 chmod
     eg. chmod("foo", 0600) will change permission of "foo" to -rw-------
   % man 2 access
     eg. access("foo", R_OK) will check if "foo" is readable
       

8. Compile with "-W -Wall -Werror -pedantic" to receive full credit.
9. It is always a good practice to check the return values of system/function calls.