Notizen und Beispiele 28.1.2021

20210128/dynmem-1.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  char **name = malloc (3 * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < 3; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-10.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  N++;
+  char **new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  name = new_name;
+  free (new_name);
+  name[N - 1] = "Dieter";
+
+  N++;
+  new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  name = new_name;
+  free (new_name);
+  name[N - 1] = "Emma";
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-11.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  N++;
+  char **new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  free (name);
+  name = new_name;
+  name[N - 1] = "Dieter";
+
+  N++;
+  new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  free (name);
+  name = new_name;
+  name[N - 1] = "Emma";
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-12.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  N++;
+  char **new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    {
+      new_name[i] = name[i];
+      free (name[i]);
+    }
+  free (name);
+  name = new_name;
+  name[N - 1] = "Dieter";
+
+  N++;
+  new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    {
+      new_name[i] = name[i];
+      free (name[i]);
+    }
+  free (name);
+  name = new_name;
+  name[N - 1] = "Emma";
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-13.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int N = 3;
+char **name = NULL;
+
+void insert_string (char *s)
+{
+  N++;
+  char **new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  free (name);
+  name = new_name;
+  name[N - 1] = s;
+}
+
+int main (void)
+{
+  name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  insert_string ("Dieter");
+  insert_string ("Emma");
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-14.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int N = 3;
+char **name = NULL;
+
+void insert_string (char *s)
+{
+  N++;
+  name = realloc (name, N * sizeof (char *));
+  name[N - 1] = s;
+}
+
+int main (void)
+{
+  name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  insert_string ("Dieter");
+  insert_string ("Emma");
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-2.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  char **name = malloc (3 * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < 3; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  name[3] = "Dieter";
+
+  printf ("\n");
+  for (int i = 0; i < 4; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-3.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  N++;
+  name[3] = "Dieter";
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-4.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  for (int i = 0; i < 10; i++)
+    {
+      N++;
+      name[3] = "Dieter";
+    }
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-5.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  N++;                      /* Falsch! */
+  name[3] = "Dieter";
+  N++;
+  name[4] = "Emma";         /* Ausgabe führt zu Absturz! */
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-6.c

+#include <stdio.h>
+#include <stdlib.h>
+
+void print_names (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  /* Speicherleck: Der Zeiger "name" verschwindet, aber die 24 Bytes,
+     auf die er zeigt, sind weiterhin belegt. */
+}
+
+int main (void)
+{
+  print_names ();
+  print_names ();
+  print_names ();
+  print_names ();
+  print_names ();
+  return 0;
+}

20210128/dynmem-7.c

+#include <stdio.h>
+#include <stdlib.h>
+
+void print_names (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+
+  /* Kein Speicherleck: Bevor der Zeiger "name" verschwindet,
+     geben wir die 24 Bytes, auf die er zeigt, wieder frei. */
+
+  /* Garbage Collection: Die Standard-Bibliothek der Programmiersprache
+     sorgt dafür, daß nicht mehr benötigte Speicherbereiche automatisch
+     wieder freigegeben werden. C macht das nicht. */
+}
+
+int main (void)
+{
+  print_names ();
+  print_names ();
+  print_names ();
+  print_names ();
+  print_names ();
+  return 0;
+}

20210128/dynmem-8.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  N++;
+  char **new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  name = new_name;
+  name[N - 1] = "Dieter";
+
+  N++;
+  char **new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  name = new_name;
+  name[N - 1] = "Emma";
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/dynmem-9.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main (void)
+{
+  int N = 3;
+  char **name = malloc (N * sizeof (char *));
+  name[0] = "Anna";
+  name[1] = "Berthold";
+  name[2] = "Caesar";
+
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  N++;
+  char **new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  name = new_name;
+  name[N - 1] = "Dieter";
+
+  N++;
+  new_name = malloc (N * sizeof (char *));
+  for (int i = 0; i < N - 1; i++)
+    new_name[i] = name[i];
+  name = new_name;
+  name[N - 1] = "Emma";
+
+  printf ("\n");
+  for (int i = 0; i < N; i++)
+    printf ("name[%d] = %s\n", i, name[i]);
+
+  free (name);
+  return 0;
+}

20210128/hp-20210128.tex

@@ -824,7 +824,7 @@
 
     ...
 
-      free (name)
+      free (name);
         /* Speicherplatz freigeben */
 
   \end{lstlisting}
@@ -880,8 +880,8 @@
           \put(-2.75,-0.05){\tikz{\draw[thick](0,0.25)--(2.5,-0.05);%
                                   \draw[thick](-0.1,-0.05)--(2.5,0.3);}}
           \put(1.5,-1.1){\begin{rotate}{7}\large\bf\textarrow\
-                           kommt gleich
-%                           nächste Woche
+%                           kommt gleich
+                           nächste Woche
                          \end{rotate}}
         \end{picture}
         Zeiger, die im Objekt gespeichert sind\\

20210128/strings-1.c

+#include <stdio.h>
+
+int main (void)
+{
+  char *hello = "Hello";
+  hello[1] = 'a';
+  printf ("%s\n", hello);
+  return 0;
+}

20210128/strings-2.c

+#include <stdio.h>
+
+int main (void)
+{
+  char hello[] = "Hello";
+  hello[1] = 'a';
+  printf ("%s\n", hello);
+  return 0;
+}