From a481bec3ba9a5e07090bcba8359edf2c4002cb8a Mon Sep 17 00:00:00 2001
From: Tibor Bizjak <tibor.bizjak@gmail.com>
Date: Tue, 18 Jul 2023 23:48:37 +0200
Subject: [PATCH] rewrote readlines

---
 k&r/05-pointers-and-arrays/05-07-sort.c | 104 ++++++++++--------------
 1 file changed, 44 insertions(+), 60 deletions(-)

diff --git a/k&r/05-pointers-and-arrays/05-07-sort.c b/k&r/05-pointers-and-arrays/05-07-sort.c
index d52771e..6a8015e 100644
--- a/k&r/05-pointers-and-arrays/05-07-sort.c
+++ b/k&r/05-pointers-and-arrays/05-07-sort.c
@@ -1,41 +1,36 @@
 #include <stdio.h>
-#include <string.h>
-#include <limits.h>
-#include <assert.h>
+#include <ctype.h>
 
 /* array bounds */
-#define MAXLINES 10
-#define BUFF_SIZE 1000
-
-/* error return values */
-#define GETLINE_OVERFLOW -2
-#define READLINES_OVERFLOW -1
+#define MAXLINES 100
+#define BUFF_SIZE (80 * 100)
 
 int readlines(char *lines[], int maxlines, char *ln_buff, size_t lb_size);
 void writelines(char *lines[], int n);
 void qsort_string(char *v[], int left, int right);
 
+/* sorts lines from stdin and prints them */
 int main()
 {
     char *lines[MAXLINES]; 
-    char ln_buff[BUFF_SIZE];
+    char buffer[BUFF_SIZE];
     
-    int line_count = readlines(lines, MAXLINES, ln_buff, BUFF_SIZE);
-
+    int line_count = readlines(lines, MAXLINES, buffer, BUFF_SIZE);
     if (line_count >= 0) {
         qsort_string(lines, 0, line_count-1);
         writelines(lines, line_count);
-    } else if (line_count == READLINES_OVERFLOW) {
-        puts("error: too many lines!");
+    } else if (line_count == -1) {
+        puts("error: lines overflow");
         return 1;
-    } else if (line_count == GETLINE_OVERFLOW) {
-        puts("error: line too long!");
+    } else if (line_count == -2) {
+        puts("error: buffer overflow");
         return 2;
     }
     return 0;
 }
 
 /* ---------- reading/printing functions */
+#include <string.h>
 /* writelines: prints n lines */
 void writelines(char *lines[], int n)
 {
@@ -43,49 +38,44 @@ void writelines(char *lines[], int n)
         printf("%s\n", *lines++);
 }
 
-int getln(char *ln_buff, size_t size);
-
-/* readlines: reads lines from input, writing them to ln_buff and line 
- * start pointers to lines. returns number of lines read or
- * GETLINE_OVERFLOW or READLINES_OVERFLOW */
-int readlines(char *lines[], int maxlines, char *ln_buff, size_t lb_size)
+/* readlines: reads lines from input, writing them to ln_buff
+ * and line pointers to lines. returns number of lines read,
+ * -1 on lines overflow
+ *  -2 on buffer overflow */
+int readlines(char *lines[], int maxlines, char *buffer, size_t buff_size)
 {
-    assert(maxlines);
-    int len;
-    char ** const lines_start = lines;
+    char ** const fst_line = lines;
+    char *ln_start = buffer;
+    int c, not_empty = 0;
 
-    while ((len = getln(ln_buff, lb_size)) >= 0 && --maxlines) {
-        *lines++ = ln_buff;
-        ln_buff += len + 1;
-        lb_size -= len + 1;
+    for (; (c = getchar()) != EOF && buff_size; --buff_size) {
+        not_empty |= !isspace(c);
+        if (c == '\n') {
+            if (!not_empty) { /* skip empty lines */
+                buff_size += buffer - ln_start;
+                buffer = ln_start;
+                continue;
+            }
+            *buffer++ = '\0';
+            *lines++ = ln_start;
+            if (!--maxlines)
+                break;
+            not_empty = 0;
+            ln_start = buffer;
+        } else
+            *buffer++ = c; 
     }
-
-    if (!maxlines)
-        return READLINES_OVERFLOW;
-    if (len == GETLINE_OVERFLOW)
-        return GETLINE_OVERFLOW;
-    if (*ln_buff) 
-        *lines++ = ln_buff;
-    return lines - lines_start;
+    /* ignore trailing whitespace and emepty lines */
+    while (c != EOF && isspace(c))
+            c = getchar();
+    if (!maxlines && c != EOF) /* lines overflow */
+        return -1;
+    if (!buff_size && c != EOF) /* buffer overflow */
+        return -2;
+    return lines - fst_line;
 }
 
-/* getln: gets line from stdin and writes it to ln_buff
- * returns line length (without '\n') or EOF or GETLINE_OVERFLOW */
-int getln(char *ln_buff, size_t size)
-{
-    assert(size);
-    char * const ln_start = ln_buff;
-    size = (size > INT_MAX) ? INT_MAX : size;
-    int c;
-    while ((c = getchar()) != EOF && c != '\n' && --size)
-        *ln_buff++ = c;
-    if (!size)
-       return GETLINE_OVERFLOW;
-    *ln_buff = '\0';
-    return (c == EOF) ? EOF : ln_buff - ln_start;
-}
-
-/* ---------- sorting functions */
+/* ---------- string quicksort */
 /* swap: swap v[i] and v[j] */
 void swap(char *v[], int i, int j)
 {
@@ -113,9 +103,3 @@ void qsort_string(char *v[], int left, int right)
     qsort_string(v, last+1, right);
 }
 
-/* ---------- static asserts */
-#define assert_diff(a, b) static_assert(a != b, #a " equals " #b)
-assert_diff(GETLINE_OVERFLOW, EOF);
-assert_diff(GETLINE_OVERFLOW, READLINES_OVERFLOW);
-#undef assert_diff
-