ptrint: Module for encoding integers into void * pointers

[ccan] / ccan / ptrint / _info

diff --git a/ccan/ptrint/_info b/ccan/ptrint/_info
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+#include "config.h"
+#include <stdio.h>
+#include <string.h>
+
+/**
+ * ptrint - Encoding integers in pointer values
+ *
+ * Library (standard or ccan) functions which take user supplied
+ * callbacks usually have the callback supplied with a void * context
+ * pointer.  For simple cases, it's sometimes sufficient to pass a
+ * simple integer cast into a void *, rather than having to allocate a
+ * context structure.  This module provides some helper macros to do
+ * this relatively safely and portably.
+ *
+ * The key characteristics of these functions are:
+ *     ptr2int(int2ptr(val)) == val
+ * and
+ *      !int2ptr(val) == !val
+ * (i.e. the transformation preserves truth value).
+ *
+ * Example:
+ *     #include <ccan/ptrint/ptrint.h>
+ *
+ *     static void callback(void *opaque)
+ *     {
+ *             int val = ptr2int(opaque);
+ *             printf("Value is %d\n", val);
+ *     }
+ *
+ *     void (*cb)(void *opaque) = callback;
+ *
+ *     int main(int argc, char *argv[])
+ *     {
+ *             int val = 17;
+ *
+ *             (*cb)(int2ptr(val));
+ *             exit(0);
+ *     }
+ *
+ * License: CC0 (Public domain)
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ */
+int main(int argc, char *argv[])
+{
+       /* Expect exactly one argument */
+       if (argc != 2)
+               return 1;
+
+       if (strcmp(argv[1], "depends") == 0) {
+               printf("ccan/build_assert\n");
+               return 0;
+       }
+       if (strcmp(argv[1], "testdepends") == 0) {
+               printf("ccan/array_size\n");
+               return 0;
+       }
+
+       return 1;
+}