linux g++ undefined reference to `dlopen'類問題

main.cpp:(.text+0x19): undefined reference to `dlopen'
main.cpp:(.text+0x22): undefined reference to `dlerror'
main.cpp:(.text+0x62): undefined reference to `dlsym'
需要在編譯時加上-ldl。
將原來的編譯命令：g++ cfgfile.cpp create.cpp main.cpp -o main
修改爲：g++ cfgfile.cpp create.cpp main.cpp -o main -ldl