Solve Exercise 5-17: field sorting

2 files changed, 268 insertions, 1 deletions

diff --git a/ch5/5-16_dir-order.c b/ch5/5-16_dir-order.c
index 7533b3b..4610ea6 100644
--- a/ch5/5-16_dir-order.c
+++ b/ch5/5-16_dir-order.c
@@ -158,7 +158,7 @@ char *alloc(int n) {
 }
 
 /* sort input lines */
-int main (int argc, char *argv[]) {
+int main(int argc, char *argv[]) {
 	int nlines;        /* number of input lines read */
 
 	if (argc > 1) {
diff --git a/ch5/5-17_field-sort.c b/ch5/5-17_field-sort.c
new file mode 100644
index 0000000..c086053
--- /dev/null
+++ b/ch5/5-17_field-sort.c
@@ -0,0 +1,267 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 5-17: Add a field-handling capability, so sorting may be done on
+ * fields within lines, each field sorted according to an independent set of
+ * options. (The index of this book was sorted with -df for the index
+ * category and -s for the page numbers.)
+ *
+ * Notes: The directions for this exercise are ambiguous. Given that this book
+ * is meant to teach and keep things mostly simple, I opted for a program that
+ * allows you to sort its input by a single field, using any sorting option
+ * previously available. For the index, then, this program would need to be
+ * ran multiple times to get the desired result. Sorting multiple ways at once
+ * on different fields at once is a complexity level far beyond what's been
+ * covered at this point in the book, so I don't think that was the intended
+ * goal. Enough jabbering; code time!
+ */
+
+
+#define MAXLINES 5000
+#define MAXLEN 1000
+#define DEFAULT_LINES 10
+#define ALLOCSIZE 10000000
+#define DELIMITER '\t'
+
+char *lineptr[MAXLINES];
+static char allocbuf[ALLOCSIZE];
+static char *allocp = allocbuf;
+int numeric = 0;   /* 1 if numeric sort */
+int reverse = 0;   /* 1 if reverse sort */
+int fold = 0;      /* 1 if folding upper and lower case */
+int dir = 0;       /* 1 if directory order */
+int fieldnum = 0;  /* Field to sort by, starting with 0. (This only gets used with -F) */
+
+char *alloc(int);
+int field_len(const char *);
+int field_start(const char *, int);
+int fieldcmp(const char *, const char *);
+int istrcmp(const char *, const char *);
+int mystrcmp(const char *, const char *);
+int numcmp(const char *, const char *);
+int readlines(char *lineptr[], int nlines);
+void my_qsort(void *lineptr[], int left, int right, int (*comp)(const char *, const char *));
+void reverse_set(char *lineptr[], int nlines);
+void writelines(char *lineptr[], int nlines);
+
+int mygetline(char *line, int lim) {
+	int c, i;
+	for (i = 0; i < lim && (c = getchar()) != EOF && c != '\n'; i++) {
+		*(line++) = c;
+	}
+	if (c == '\n') {
+		i++; /* I count newlines; some don't */
+		*(line++) = c;
+	}
+	*line = '\0';
+	return i;
+}
+
+void my_qsort(void *v[], int left, int right, int (*comp)(const char *, const char *)) {
+	int i, last;
+	void swap(void *v[], int, int);
+
+	if (left >= right) {
+		return;
+	}
+	swap(v, left, (left + right) / 2);
+	last = left;
+	for (i = left + 1; i <= right; i++) {
+		if ((*comp)(v[i], v[left]) <= 0) {
+			swap(v, ++last, i);
+		}
+	}
+	swap(v, left, last);
+	my_qsort(v, left, last - 1, comp);
+	my_qsort(v, last + 1, right, comp);
+}
+
+int numcmp(const char *s1, const char *s2) {
+	double v1, v2;
+	v1 = atof(s1);
+	v2 = atof(s2);
+	if (v1 < v2) {
+		return -1;
+	} else if (v1 > v2) {
+		return 1;
+	} else {
+		return 0;
+	}
+}
+
+void swap(void *v[], int i, int j) {
+	void *temp;
+	temp = v[i];
+	v[i] = v[j];
+	v[j] = temp;
+}
+
+int readlines(char *lineptr[], int maxlines) {
+	int len, nlines;
+	char *p, line[MAXLEN];
+	nlines = 0;
+	while ((len = mygetline(line, MAXLEN)) > 0) {
+		if (nlines >= maxlines || (p = alloc(len)) == NULL) {
+			return -1;
+		} else {
+			line[len-1] = '\0';
+			strcpy(p, line);
+			lineptr[nlines++] = p;
+		}
+	}
+	return nlines;
+}
+
+void writelines(char *lineptr[], int nlines) {
+	int i = 0;
+	for (; i < nlines && lineptr[i] != NULL; i++) {
+		printf("%s\n", lineptr[i]);
+	}
+}
+
+void reverse_set(char *lineptr[], int nlines) {
+	int i;
+	int j = nlines;
+	for (i = 0; i < (nlines / 2); i++, j--) {
+		if (i < nlines) {
+			swap((void **)lineptr, i, j);
+		}
+	}
+}
+
+/* Ignore character case, then send results to qsort */
+int mystrcmp(const char *s1, const char *s2) {
+	if (dir) {
+		while (!isalpha(*s1) && !isspace(*s1) && isdigit(*s1)) {
+			s1++;
+		}
+		while (!isalpha(*s2) && !isspace(*s2) && isdigit(*s2)) {
+			s2++;
+		}
+	}
+	while ((fold ? (tolower(*s1) == tolower(*s2)) : (*s1 == *s2))) {
+		if (*s1 == '\0') {
+			return 0;
+		}
+		s1++;
+		s2++;
+		if (dir) {
+			while (!isalpha(*s1) && !isspace(*s1) && isdigit(*s1)) {
+				s1++;
+			}
+			while (!isalpha(*s2) && !isspace(*s2) && isdigit(*s2)) {
+				s2++;
+			}
+		}
+	}
+	return (fold ? (tolower(*s1) - tolower(*s2)) : (*s1 - *s2));
+}
+
+int field_start(const char *s, int fieldnum) {
+	if (fieldnum == 0) {
+		return 0;
+	}
+	int i;
+	for (i = 0; s[i] != '\0'; i++) {
+		if (s[i] == DELIMITER) {
+			fieldnum--;
+			if (fieldnum == 0) {
+				if (s[i+1] != '\0') {
+					return i+1;
+				}
+			}
+		}
+	}
+	return -1;
+}
+
+int field_len(const char *s) {
+	int i = 0;
+	while (s[i] != '\0') {
+		if (s[i] == DELIMITER) {
+			return i;
+		}
+		i++;
+	}
+	return i; /* If we reach the end of the string, we should return */
+}
+
+/* Produces substring copies of the fields to be compared, then hands it off
+ * to a comparison function.
+ */
+int fieldcmp(const char *s1, const char *s2) {
+	char tmp1[MAXLEN];
+	char tmp2[MAXLEN];
+	int start1 = field_start(s1, fieldnum);
+	int start2 = field_start(s2, fieldnum);
+	int len1 = field_len(s1 + start1);
+	int len2 = field_len(s2 + start2);
+	/* It should be safe to use strncpy here since we've established the
+	 * boundaries of the field within the extant source strings
+	 */
+	strncpy(tmp1, s1 + start1, len1);
+	tmp1[len1] = '\0';
+	strncpy(tmp2, s2 + start2, len2);
+	tmp2[len2] = '\0';
+	return (numeric ? numcmp(tmp1, tmp2) : (fold || dir) ? mystrcmp(tmp1, tmp2) : strcmp(tmp1, tmp2));
+}
+
+char *alloc(int n) {
+	if (allocbuf + ALLOCSIZE - allocp >= n) {
+		allocp += n;
+		return allocp - n;
+	} else {
+		return 0;
+	}
+}
+
+/* sort input lines */
+int main(int argc, char *argv[]) {
+	int nlines;        /* number of input lines read */
+	if (argc > 1) {
+		int i, j;
+		for (i = 1, j = 0; --argc; i++) {
+			if (argv[i][j++] == '-') {
+				while (argv[i][j] != '\0') {
+					switch(argv[i][j]) {
+						case 'n':
+							numeric = 1;
+							break;
+						case 'r':
+							reverse = 1;
+							break;
+						case 'f':
+							fold = 1;
+							break;
+						case 'd':
+							dir = 1;
+							break;
+						case 'F':
+							if (isdigit(argv[i][++j])) {
+								fieldnum = (argv[i][j] - '0');
+							}
+							break;
+					}
+					j++;
+				}
+			}
+		}
+	}
+	if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
+		/* The trick is to chain inline if-statements. This will point to the correct
+		function for comparison, which powers my_qsort */
+		my_qsort((void **) lineptr, 0, nlines - 1, (int (*)(const char *, const char *))(fieldnum >= 0 ? fieldcmp : (numeric ? numcmp : (fold || dir ? mystrcmp : strcmp))));
+		if (reverse == 1) {
+			reverse_set(lineptr, nlines - 1);
+		}
+		writelines(lineptr, nlines);
+		return 0;
+	} else {
+		printf("Input too big to sort\n");
+		return 1;
+	}
+}