Libnodave is a library that provides the necessary functions to connect to and exchange data with Siemens S7 300/400 PLCs (200 family and S5 family now also supported).
Can now also be used under Win32.
https://sourceforge.net/projects/libnodave/
LIBNODAVE-Exchange data with Siemens PLCs 西门子PLC设备开源驱动库