5.4

Author: Heatwave

chapter-5-pointers-and-arrays/6.alloc.c

@@ -0,0 +1,20 @@
+#define ALLOCSIZE 10000
+
+static char allocbuf[ALLOCSIZE];
+static char *allocp = allocbuf;
+
+char *alloc(int n)
+{
+	if (allocbuf + ALLOCSIZE - allocp >= n) {
+		allocp += n;
+		return allocp - n;
+	} else
+		return 0;
+}
+
+void afree(char *p)
+{
+	if (p >= allocbuf && p < allocbuf + ALLOCSIZE)
+		allocp = p;
+}
+

chapter-5-pointers-and-arrays/7.alloc.test.c

@@ -0,0 +1,36 @@
+#include <stdio.h>
+#include <stddef.h>
+
+int main()
+{
+	char *alloc(int);
+	void afree(char*);
+
+	char *p = alloc(10);
+	if (NULL == p)
+		return -1;
+
+	*p++ = 'H';
+	*p++ = 'e';
+	*p++ = 'l';
+	*p++ = 'l';
+	*p++ = 'o';
+	*p++ = '\0';
+	p -= 6;
+
+	printf("%s\n", p);
+
+	afree(p);
+
+	printf("%s\n", p);
+
+	p = alloc(10001);
+
+	if (NULL == p)
+		printf("overflow!\n");
+
+	printf("%d\n", NULL);
+
+	return 0;
+}
+

chapter-5-pointers-and-arrays/8.strlen-address-arithmetic.c

@@ -0,0 +1,29 @@
+#include <stdio.h>
+
+int main()
+{
+	int strlen(char*);
+
+	char array[100];
+	char *ptr = "Hello";
+
+	int l = strlen("hello, world");
+	printf("%d\n", l);
+
+	l = strlen(array);
+	printf("%d\n", l);
+
+	l = strlen(ptr);
+	printf("%d\n", l);
+}
+
+int strlen(char *s)
+{
+	char *p = s;
+
+	while (*p != '\0')
+		p++;
+	
+	return p - s;
+}
+