编写一个程序splitf.c，实现对文件按指定大小进行分割，和反向合并的功能。

如果调用splitf -s afile.dat 1024，则文件afile.dat将被按1024字节为单位分割成若干个片段（最后一个片段可能不足1024字节）。产生的片段在同一个目录下以不同的文件保存，以片段编号为其文件后缀，例如：afile.001、afile.002、afile.003、……

如果调用splitf -m afile.dat 020，则当前目录下的片段文件afile.001、afile.002、……、afile.020将依次被合并并形成afile.dat。注意：若某个片段缺失，则应该提示合并失败-The preparation of a program splitf.c, realize the document specified partition size, and the function of reverse merger. If the call splitf-s afile.dat 1024, the document will be afile.dat by 1024 bytes divided into several fragments (a fragment of a possible shortage of the last 1024 bytes). Fragment generated in the same directory with different files to fragment number for the file suffix, such as: afile.001, afile.002, afile.003, ... ... If you call splitf-m afile.dat 020, while the current directory under the document fragment afile.001, afile.002, ... ..., afile.020 will in turn be combined and formed afile.dat. Note: If a fragment is missing, they should be prompted to merge failure