hello: execute hello.lua to get the output stringHEADscripted-hellomaster

2 files changed, 49 insertions, 1 deletions

diff --git a/hello.c b/hello.c
index 2d719e1..8e3f2c4 100644
--- a/hello.c
+++ b/hello.c
@@ -1,6 +1,53 @@
 #include <stdio.h>
 
+/* lua.h provides core functions, these include everything starting lua_ */
+#include <lua.h>
+/* lauxlib.h provides convenience functions, these start luaL_ */
+#include <lauxlib.h>
+
 int main(void){
-	printf("Hello World!\n");
+	/* The lua_State structure encapsulates your lua runtime environment
+	   luaL_newstate allocates and initializes it.
+	   There also exists a lua_newstate, which takes parameters for a custom
+	   memory allocator, since the lua runtime needs to allocate memory.
+	   luaL_newstate is a wrapper, which uses the standard C library's realloc,
+	   and aborts on allocation failure.
+	 */
+	lua_State *L = luaL_newstate();
+	if (!L) {
+		perror("Creating lua state");
+		return 1;
+	}
+
+	/* The following executes the file hello.lua, which returns the string
+	   intended to be printed.
+	   Likewise it is an auxiliary function, which reads a file,
+	   compiles the contents into a function, then calls it.
+	 */
+	if (luaL_dofile(L, "hello.lua")) {
+		/* dofile returns a string on the lua stack in the case of error
+		   which says what went wrong, a pointer to it is retrieved with
+		   lua_tostring, this exists inside the lua_State structure, so
+		   if you need it after the next call to lua you have to copy it
+		 */
+		char const *errmsg = lua_tostring(L, 1);
+		fprintf(stderr, "Failed to execute hello.lua: %s\n", errmsg);
+		return 2;
+	}
+
+	/* A file can take parameters and return values like a function.
+	   The result is passed to printf, so IO is done outside of lua.
+	 */
+	char const *result = lua_tostring(L, 1);
+	if (!result) {
+		fprintf(stderr, "hello.lua did not return a string\n");
+		return 3;
+	}
+	printf("%s\n", result);
+
+	/* lua_close frees up any resources used by the lua runtime
+	   This is not necessary here, since the program is about to exit.
+	 */
+	lua_close(L);
 	return 0;
 }
diff --git a/hello.lua b/hello.lua
new file mode 100644
index 0000000..cfcbc24
--- /dev/null
+++ b/hello.lua
@@ -0,0 +1 @@
+return "Hello World!"