Add next_block() call to advance pointers over memory.

Simple call to get the pointer to the next field when operating on a wire
protocol struct or on a single-memory-block Xlib structure.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

1 files changed, 37 insertions, 0 deletions

diff --git a/src/XIint.h b/src/XIint.h
index 63e33f1..400c920 100644
--- a/src/XIint.h
+++ b/src/XIint.h
@@ -29,4 +29,41 @@ typedef struct _XInputData
     XExtensionVersion *vers;
 } XInputData;
 
+
+/**
+ * Returns the next valid memory block of the given size within the block
+ * previously allocated.
+ * Use letting pointers inside a struct point to bytes after the same
+ * struct, e.g. during protocol parsing etc.
+ *
+ * Caller is responsible for allocating enough memory.
+ *
+ * Example:
+ *    void *ptr;
+ *    struct foo {
+ *       int num_a;
+ *       int num_b;
+ *       int *a;
+ *       int *b;
+ *    } bar;
+ *
+ *    ptr = malloc(large_enough);
+ *    bar = next_block(&ptr, sizeof(struct foo));
+ *    bar->num_a = 10;
+ *    bar->num_b = 20;
+ *    bar->a = next_block(&ptr, bar->num_a);
+ *    bar->b = next_block(&ptr, bar->num_b);
+ */
+static inline void*
+next_block(void **ptr, int size) {
+    void *ret = *ptr;
+
+    if (!*ptr)
+        return NULL;
+
+    *(unsigned char**)ptr += size;
+
+    return ret;
+}
+
 #endif