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--- adt_example [2014/11/12 11:01]
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+++ adt_example [2014/11/12 11:55]
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@@ Line 1: / Line 1: @@
-===== StringList ADT =====
+===== StringSet ADT =====
 I want to give a simple example about creating **a**bstract **d**ata **t**ypes in Pelles C.
@@ Line 8: / Line 8: @@
 Therefore the implementor of an ADT writes an header file, the user may include.
-In this example we will build a string list. We declare the ADT type name as:
+In this example we will build a string set. We declare the ADT type name as:
+<code c>
+typedef struct _STRSET *STRSET;
+</code>
+All the user can see is, that ''STRSET'' is a pointer to an unknown struct ''_STRSET''.
+We will provide a set of access functions. First there are two functions who serve as cunstructors and destructores of the ADT. ''StrSetInit()'' creates an emty string set and ''StrSetFree()'' frees the string set.
+<code c>
+STRSET	StrSetInit(void);
+void	StrSetFree(STRSET ss);
+</code>
+We further provide some functions to insert a string in the ADT: ''StrSetInsert()'' and to retrieve its address: ''StrSetGetPtr()''.
+We also add some utility functions. ''StrSetSize()'' returns the number of strings in the set and ''StrSetClear()'' deletes all the strings in the set, but not the string set itself.
+<code c>
+void	StrSetClear(STRSET ss);
+int	StrSetSize(STRSET ss);
+</code>
+The whole header file ''strset.h'' is:
+<code c>
+#ifndef STRSET_H
+#define STRSET_H
+typedef struct _STRSET *STRSET;
+STRSET	StrSetInit(void);
+void	StrSetClear(STRSET ss);
+void	StrSetFree(STRSET ss);
+int	StrSetInsert(STRSET ss, int nPosition, char *s);
+int	StrSetSize(STRSET ss);
+char*	StrSetGetPtr(STRSET ss, int nPosition);
+#endif // STRSET_H
+</code>
+The user now is able to use the ADT:
+<code c>
+#include <stdio.h>
+#include <string.h>
+#include "strset.h"
+char *input(char *b)
+{
+	printf("> ");
+	scanf("%s", b);
+	return b;
+}
+int main(int argc, char *argv[])
+{
+	int i=0;
+	char buf[100] = "";				// declare a temporary buffer
+	STRSET	S = StrSetInit();			// declare the string set
+	while (strcmp(input(buf), "quit"))
+		StrSetInsert(S, i++, buf);		// insert the string in the set
+	for (i=0; i<StrSetSize(S); i++)			// loop over all the strings in the set
+		puts(StrSetGetPtr(S, i));		// get and display each string
+	StrSetFree(S);					// free the string set
+	return 0;
+}
+</code>
+Ok! That is all from the users point of view!
+However, the implementor has to create the ADT. He does this in a separate module ''strset.c'' which could be compiled to a static library, to hit its content.
+To perform this task we will use the DPA functions in ''COMCTL32.lib''.
+Here is ''strset.c'':
+<code c>
+#include <windows.h>
+#include <commctrl.h>
+#include "strset.h"
+#pragma  comment(lib, "comctl32.lib")
+struct _STRSET {
+	HDPA h;
+};
+STRSET StrSetInit(void)
+{
+	STRSET ss = malloc(sizeof(struct _STRSET));
+	if (ss) ss->h = DPA_Create(10);
+	return ss;
+}
+void StrSetClear(STRSET ss)
+{
+	if (ss)
+		for (int i=0; i<DPA_GetPtrCount(ss->h); i++) {
+			free(DPA_GetPtr(ss->h, i));
+			DPA_DeletePtr(ss->h, i);
+		}
+}
+void StrSetFree(STRSET ss)
+{
+	if (ss) {
+		StrSetClear(ss);
+		free(ss);
+	}
+}
+int StrSetInsert(STRSET ss, int nPosition, char *s)
+{
+	char *b = NULL;
+	if (ss && s) {
+		b = malloc(strlen(s)+1);
+		strcpy(b,s);
+		return DPA_InsertPtr(ss->h, nPosition, b);
+	} return -1;
+}
+int StrSetSize(STRSET ss) { return DPA_GetPtrCount(ss->h); }
+char *StrSetGetPtr(STRSET ss, int nPosition) { return DPA_GetPtr(ss->h, nPosition); }
+</code>
+As you can see, the secret struct
+<code c>
+struct _STRSET {
+	HDPA h;
+};
+</code>
+is very simple in this case. It only holds a DPA handle.
+Because the ''COMCTL32.LIB'' is needed, we instruct the linker to link against it, with the ''#pragma'' directive. So our user has not to know what additional libraries are used.
+All our ADT functions with the exception of ''StrSetInit()'' use a first parameter of type ''STRSET''. And all this access functions have to verify that this parameter is valid (not ''NULL'').
+If you have any questions? Use the [[http://forum.pellesc.de/|Pelles C forum]] to ask.

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