Lua stack dump (WRONG CASE)

	void _dumpStack(lua_State* L, const char* func, int line)
	{
	int top = lua_gettop(L);
	printf("(%s,%d) top=%d\n", func, line, top);
	for (int i = 0; i < top; i++) {
	int positive = top - i;
	int negative = -(i + 1);
	int type = lua_type(L, positive);
	const char* typeName = lua_typename(L, type);
	const char* value = lua_tostring(L, positive); // danger!!! numbers on the Lua stack will be replaced with string
	printf("%d/%d: type=%s value=%s\n", positive, negative, typeName, value);
	}
	}

view raw wrong_lua_stack_dump.cpp hosted with ❤ by GitHub

This is very simple Lua stack dumper. It extracts all element values by using lua_tostring whatever the types is not a string. It looks work well, but the problem is that lua_tostring overwrites values in the stack by string version.

One of correct code is below. The programmer always needed to take a step to ensure their correct types when accessing the Lua stack.

	void _dumpStack(lua_State* L, const char* func, int line)
	{
	int top = lua_gettop(L);
	printf("(%s,%d) top=%d\n", func, line, top);
	for (int i = 0; i < top; i++) {
	int positive = top - i;
	int negative = -(i + 1);
	int type = lua_type(L, positive);
	int typeN = lua_type(L, negative);
	assert(type == typeN);
	const char* typeName = lua_typename(L, type);
	printf("%d/%d: type=%s", positive, negative, typeName);
	switch (type) {
	case LUA_TNUMBER:
	printf(" value=%f", lua_tonumber(L, positive));
	break;
	case LUA_TSTRING:
	printf(" value=%s", lua_tostring(L, positive));
	break;
	case LUA_TFUNCTION:
	if (lua_iscfunction(L, positive)) {
	printf(" C:%p", lua_tocfunction(L, positive));
	}
	break;
	}
	printf("\n");
	}
	}

view raw correct_lua_stack_dump.cpp hosted with ❤ by GitHub