Index: src/string.c
==================================================================
--- src/string.c
+++ src/string.c
@@ -23,10 +23,11 @@
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 
 #include "object.h"
 #include "string.h"
 
@@ -145,10 +146,32 @@
 	str->data = new;
 	str->len += append->len;
 
 	return true;
 }
+
+size_t
+cfw_string_find(CFWString *str, CFWString *substr, cfw_range_t range)
+{
+	size_t i;
+
+	if (range.start > str->len)
+		return SIZE_MAX;
+
+	if (range.length == SIZE_MAX)
+		range.length = str->len - range.start;
+
+	if (range.start + range.length > str->len || substr->len > range.length)
+		return SIZE_MAX;
+
+	for (i = range.start; i <= range.start + range.length - substr->len;
+	    i++)
+		if (!memcmp(str->data + i, substr->data, substr->len))
+			return i;
+
+	return SIZE_MAX;
+}
 
 static CFWClass class = {
 	.name = "CFWString",
 	.size = sizeof(CFWString),
 	.ctor = ctor,

Index: src/string.h
==================================================================
--- src/string.h
+++ src/string.h
@@ -26,14 +26,16 @@
 
 #ifndef __COREFW_STRING_H__
 #define __COREFW_STRING_H__
 
 #include "class.h"
+#include "range.h"
 
 typedef struct CFWString CFWString;
 extern CFWClass *cfw_string;
 extern const char* cfw_string_c(CFWString*);
 extern size_t cfw_string_len(CFWString*);
 extern bool cfw_string_set(CFWString*, const char*);
 extern bool cfw_string_append(CFWString*, CFWString*);
+extern size_t cfw_string_find(CFWString*, CFWString*, cfw_range_t);
 
 #endif

Index: tests/tests.c
==================================================================
--- tests/tests.c
+++ tests/tests.c
@@ -53,10 +53,14 @@
 		cfw_string_append(s[0], cfw_array_get(a, i));
 
 	cfw_unref(a);
 
 	puts(cfw_string_c(s[0]));
+
+	s[1] = cfw_new(cfw_string, "ll");
+	printf("%zd\n", cfw_string_find(s[0], s[1], cfw_range_all));
+	cfw_unref(s[1]);
 
 	cfw_unref(s[0]);
 
 	return 0;
 }