Fix

Makefile

@@ -8,17 +8,15 @@ CXXFLAGS = -Wall -Wextra
 LDLIBS = $(shell sdl2-config --libs) $(shell sdl2-config --libs)_mixer
 
 SRC_DIR = src
-CLIENT_SRC := $(wildcard $(SRC_DIR)/client*.cpp)
-SERVER_SRC := $(wildcard $(SRC_DIR)/server*.cpp)
+CLIENT_SRC = $(wildcard $(SRC_DIR)/client*.cpp)
+SERVER_SRC = $(wildcard $(SRC_DIR)/server*.cpp)
 
-# Heavily inspired by https://stackoverflow.com/a/30602701
 BUILD_DIR = build
 BIN_DIR = $(BUILD_DIR)/bin
-OBJ_DIR = $(BUILD_DIR)/obj
-CLIENT_OBJ := $(CLIENT_SRC:$(SRC_DIR)/%.cpp=$(OBJ_DIR)/%.o)
-SERVER_OBJ := $(SERVER_SRC:$(SRC_DIR)/%.cpp=$(OBJ_DIR)/%.o)
-
 PROGRAM = $(BIN_DIR)/client $(BIN_DIR)/server
+OBJ_DIR = $(BUILD_DIR)/obj
+CLIENT_OBJ = $(patsubst $(SRC_DIR)/%.cpp, $(OBJ_DIR)/%.o, $(CLIENT_SRC))
+SERVER_OBJ = $(patsubst $(SRC_DIR)/%.cpp, $(OBJ_DIR)/%.o, $(SERVER_SRC))
 
 .DELETE_ON_ERROR:
 .PHONY: all clean