add include

.vscode/settings.json

@@ -7,7 +7,8 @@
         "lib.h": "c",
         "common.h": "c",
         "modulator.h": "c",
-        "control_pipe.h": "c"
+        "control_pipe.h": "c",
+        "stdlib.h": "c"
     },
     "C_Cpp.codeAnalysis.clangTidy.checks.disabled": [
         "clang-diagnostic-error"

src/common.h

@@ -1,3 +1,4 @@
+#include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>