C - 高度な関数 - 関数を最大限に活用する(stdlib.h ヘッダファイル、qsort関数(クイックソート))

Head First C
原著

開発環境

• OS: macOS High Sierra - Apple
• Text Editor: Emacs
• コンパイラー: LLVM/Clang, GCC(gcc)
• プログラミング言語: C

Head First C ―頭とからだで覚えるCの基本 (David Griffiths (著)、Dawn Griffiths (著)、中田 秀基 (監修)、木下 哲也 (翻訳)、オライリージャパン)の7章(高度な関数 - 関数を最大限に活用する)、長いエクササイズ(p. 328)を取り組んでみる。

長いエクササイズ(p. 328)

Makefile

CC = cc

all: run

sample: sample.c
 $(CC) sample.c -o sample

run: sample
 ./sample

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int scores_n = 7;
int scores[] = {543, 323, 32, 554, 11, 3, 112};

void scores_display() {
  puts(__func__);
  for (int i = 0; i < scores_n; i++) {
    printf("%i\n", scores[i]);
  }
}
int compare_scores(const void *score_a, const void* score_b) {
  int a = *(int*)score_a;
  int b = *(int*)score_b;
  return a - b;
}

int compare_scores_desc(const void* score_a, const void* score_b) {
  return compare_scores(score_b, score_a);
}

typedef struct {
  int width;
  int height;
} Rectangle;

int rects_n = 5;
Rectangle rects[] = {
  {1, 1},
  {1, 5},
  {1, 2},
  {1, 4},
  {1, 3}
};
void rects_display() {
  puts(__func__);
  for (int i = 0; i < rects_n; i++) {
    printf("%i x %i\n", rects[i].width, rects[i].height);
  }
}

int compare_areas(const void* a, const void* b) {
  Rectangle *rect_a = (Rectangle*)a;
  Rectangle *rect_b = (Rectangle*)b;

  int area_a = rect_a->width * rect_a->height;
  int area_b = rect_b->width * rect_b->height;

  return area_a - area_b;
}
int names_n = 5;
char *names[] = {
  "a",
  "e",
  "b",
  "d",
  "c"
};
void names_display() {
  puts(__func__);
  for (int i = 0; i < names_n; i++) {
    puts(names[i]);
  }
}
int compare_names(const void *a, const void* b) {
  char **name_a = (char**)a;
  char **name_b = (char**)b;

  return strcmp(*name_a, *name_b);
}

int compare_areas_desc(const void*a, const void*b) {
  return compare_areas(b, a);
}

int compare_names_desc(const void* a, const void* b) {
  return compare_names(b, a);
}

int main() {
  scores_display();
  qsort(scores, scores_n, sizeof(int), compare_scores);
  scores_display();
  qsort(scores, scores_n, sizeof(int), compare_scores_desc);
  scores_display();

  rects_display();
  qsort(rects, rects_n, sizeof(Rectangle), compare_areas);
  rects_display();
  qsort(rects, rects_n, sizeof(Rectangle), compare_areas_desc);
  rects_display();

  names_display();
  qsort(names, names_n, sizeof(char*), compare_names);
  names_display();
  qsort(names, names_n, sizeof(char*), compare_names_desc);
  names_display();
}

入出力結果(Terminal)

$ make
cc sample.c -o sample
./sample
scores_display
543
323
32
554
11
3
112
scores_display
3
11
32
112
323
543
554
scores_display
554
543
323
112
32
11
3
rects_display
1 x 1
1 x 5
1 x 2
1 x 4
1 x 3
rects_display
1 x 1
1 x 2
1 x 3
1 x 4
1 x 5
rects_display
1 x 5
1 x 4
1 x 3
1 x 2
1 x 1
names_display
a
e
b
d
c
names_display
a
b
c
d
e
names_display
e
d
c
b
a
$