Update: move the declarations out of the ifdef

becs.h

@@ -1,29 +1,37 @@
 #ifndef BECS_H
 #define BECS_H
 
-
-#ifdef BECS_IMPLEMENTATION
 #include <stdint.h>
 
-typedef struct BECS_ComponentArray {
+typedef struct BECS_ComponentArray BECS_ComponentArray;
+typedef struct BECS_Properties BECS_Properties;
+typedef struct BECS_ECS BECS_ECS;
+
+size_t BECS_GetMinMemorySize(BECS_Properties props);
+BECS_ECS *BECS_Init(void *memory, size_t size, BECS_Properties *props);
+int32_t BECS_AddComponent(BECS_ECS *ecs, uint32_t entityID, uint64_t componentBitMask, void *component);
+
+#ifdef BECS_IMPLEMENTATION
+
+struct BECS_ComponentArray {
     uint32_t lastEntityAdded;
     size_t unitSize;
     uint32_t length;
     uint32_t capacity;
     void *array;
-} BECS_ComponentArray;
+};
 
-typedef struct BECS_Properties {
+struct BECS_Properties {
     uint32_t maxEntities;
     uint32_t numComponents;
     size_t *componentSizes;
-} BECS_Properties;
+};
 
-typedef struct BECS_ECS {
+struct BECS_ECS {
     uint64_t *bitMasks;
     BECS_Properties props;
     BECS_ComponentArray *componentSets;
-} BECS_ECS;
+};
 
 size_t BECS_GetMinMemorySize
 (BECS_Properties props)

build.bat

@@ -1 +1,8 @@
+@echo off
 REM Build Script for BECS
+
+mkdir build
+
+pushd ".\build"
+cl /GR- /Oi /EHa- /MTd /Zi "..\test\main.c"
+popd

build.sh

@@ -1 +1,3 @@
 # Build script for BECS
+
+echo "Build Script not written"

test/main.c

@@ -2,7 +2,7 @@
 #include <stdlib.h>
 
 #define BECS_IMPLEMENTATION
-#include "becs.h"
+#include "../becs.h"
 
 typedef struct compA {
 	uint32_t thing;