Software 1 - const, getopt & photo (7)

administrivia

Web Page - http://www.cs.tau.ac.il/~efif/courses/Software1_Spring_04

Riddle

Find three ways to change one character in the code bellow so that the resulting code will print 20 times the minus sign ('-').
- Remember, you can change one character only for each solution.
int i, n=20; for (i = 0; i < n; i--) printf("-");

Constants in C

Using the preprocessor directive #define
#define pi 3.1415
Using const variables
const float pi = 3.1415;

Using enumerations

enum days {monday=1,tuesday,wednesday,thursday,friday,saturday,sunday};

const

The compiler catches attempts to modify variables that have been declared const.

int main(void)
{
  const char * a; /* pointer to elements of type "const char" */
  char * const b; /* constant pointer to elements of type "char" */
  char *c, *d;

  // some initialization code for a, c, d comes here ...
  // note that b can only be assigned at declaration above

  a = c;// correct
  b = d;// wrong


  a[0] = 'e';// wrong
  b[0] = 'f';// correct
  return 0;
}

Illustration

getopt

parse command line options

int getopt(int argc, char * const argv[], const char *optstring);

getopt global variables

char * optarg = NULL;
int opterr = 1;
int optind = 1;
int optopt = 0;

getopt - an example of usage

static void print_help(char * progName)
{
  printf("Usage: %s [options]\n\
  -h \t\t\tprint this help message\n\
  -i \t\tset the ineteger\n\
  -f \tset the floating point number\n\
  -s \t\tset the string\n\
  -u \tset the unsigned integer\n\
  -v \t\t\ttoggle verbose\n", progName);
}

char optionStr[] = "hf:i:s:u:v";

#if defined(_MSC_VER)
#define DIR_SEP '\\'
#else
#define DIR_SEP '/'
#endif

int main(int argc, char * argv[])
{
  int c;
  int integer = 0;
  double floating_point = 0.0;
  char * str = 0;
  unsigned int unsigned_integer = 0;
  int verbose = 0;
  
  progName = strrchr(argv[0], DIR_SEP);
  progName = (progName) ? progName+1 : argv[0];

  while ((c = getopt(argc, argv, optionStr)) != EOF) {
    switch (c) {
     case 'h': print_help(progName); return 1;
     case 'i': integer = atoi(optarg); break;
     case 'f': floating_point = atof(optarg); break;
     case 's': str = optarg; break;
     case 'u': unsigned_integer = strtoul(optarg, 0, 0); break;
     case 'v': verbose = !verbose; break;

     default:
      fprintf(stderr, "Try `%s -h' for more information.\n", progName);
      return -1;
    }
  }

  if (verbose) {
    printf("%17s %d\n", "integer:", integer);
    printf("%17s %f\n", "floating point:", floating_point);
    printf("%17s 0x%x\n", "unsigned integer:", unsigned_integer);
    printf("%17s %s\n", "string:", (str) ? str : "");
    printf("\noptind: %d\n", optind);
  }
  return 0;
}

my_getopt.c

PPM - portable pixmap file format

A lowest common denominator color image file format
A PPM file consists of a sequence of one or more PPM images
- there are no data, delimiters, or padding before, after, or between images.
Each PPM image consists of the following
- A "magic number" for identifying the file type. A ppm image's magic number is the two characters "P6". Whitespace (blanks, TABs, CRs, LFs).
- A width, formatted as ASCII characters in decimal. Whitespace
- A height, again in ASCII decimal. Whitespace
- The maximum color value (Maxval), again in ASCII decimal. Must be less than 65536. Whitespace
- A raster of Width * Height pixels, proceeding through the image in normal English reading order. Each pixel is a triplet of red, green, and blue samples, in that order. Each sample is represented in pure binary by either 1 or 2 bytes. If the Maxval is less than 256, it is 1 byte. Otherwise, it is 2 bytes. The most significant byte is first.

Gray scale

Convert color to gray scale

void gray_image()
{
  int i, j, k = 0;
  GLubyte r, g, b, x;
  for (j = 0; j < image_height; j++) {
    for (i = 0; i < image_width; i++) {
      r = image[k];
      g = image[k+1];
      b = image[k+2];
      x = (r + g + b) / 3;
      image[k] = x;
      image[k+1] = x;
      image[k+2] = x;
      k += 3;
    }
  }
}

Reflect horizontally


/*! Swap lines i and j of the image */
void swap_image_line(int i, int j)
{
  int k;
  unsigned char tmp;
  int lineSize = image_width * 3;
  unsigned char * s1 = &image[i * lineSize];
  unsigned char * s2 = &image[j * lineSize];
  for (k = 0; k < lineSize; ++k) {
    tmp = s1[k];
    s1[k] = s2[k];
    s2[k] = tmp;
  }
}

/*! Reflect the image about a central horizontal line */
void reflect_hor_image(void)
{
  int half = image_height / 2;
  int i;
  for (i = 0; i < half; i++) swap_image_line(i, image_height - 1 - i);
}

photo

photo.c
cp_photo.c
photo.ppm

Compile and link commans

Linux
gcc -Wall -lglut -o photo photo.c

Windows cygwin

gcc -Wall -lglut32 -lopengl32 -o photo photo.c

Windows MSVC

cl -nologo -c cp_photo.c
link -nologo -subsystem:console -libpath:lib glut32.lib opengl32.lib cp_photo.obj

Maintained by Efi Fogel. Last modified: April 24 2004.