I ve used netpbm format a few time when I needed something simple.
That s how I found out that qsort() (in my implementation and for the data provided) performs a merge sort!
Source code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#define ARRAY_SIZE 20
#define MAX_VALUE 10
unsigned char arr[ARRAY_SIZE];
void print_array(const void *left, const void *right) {
static int imgs = 0;
int k, j;
FILE *img;
char fname[100];
char rgb[100];
if (++imgs > 9999) return;
sprintf(fname, "img/img%04d.ppm", imgs);
/* create image in "img/" directory */
img = fopen(fname, "w");
if (img) {
fprintf(img, "P3
%d %d
255
", ARRAY_SIZE, MAX_VALUE);
for (j=0; j<MAX_VALUE; j++) {
for (k=0; k<ARRAY_SIZE; k++) {
int colour = 0;
if (left && left == arr+k) colour = 2;
if (right && right == arr+k) colour = 2;
if (arr[k] == MAX_VALUE - j - 1) colour = 1;
switch (colour) {
default: sprintf(rgb, "%d %d %d", 255, 255, 255); break;
case 1: sprintf(rgb, "%d %d %d", 0, 0, 0); break;
case 2: sprintf(rgb, "%d %d %d", 255, 0, 0); break;
}
}
fprintf(img, "%s
", rgb);
}
}
fclose(img);
} else {
perror("img fopen");
}
}
int cmp(const void *left, const void *right) {
const unsigned char a = *(const unsigned char*)left;
const unsigned char b = *(const unsigned char*)right;
print_array(left, right);
if (a < b) return -1;
if (a == b) return 0;
return 1;
}
int main(void) {
int k;
unsigned int seed = 0; /* or time(0) */
srand(seed);
for (k=0; k<ARRAY_SIZE; k++) {
arr[k] = rand() % MAX_VALUE;
}
print_array(NULL, NULL);
qsort(arr, (size_t)ARRAY_SIZE, sizeof *arr, cmp);
print_array(NULL, NULL);
/* use imagemagick to convert group of files to .gif */
system("convert -delay 0"
" img/img*.ppm"
" -loop 1 img/libc-qsort2.gif");
/* remove .ppm files */
system("rm img/" "*ppm"); /* ... my editor does not like a
slash and a star together,
even inside quotes */
return 0;
}
