DOS UNIX Win16 #include<stddef.h>
    OS/2 Win32    size_t offsetof(struct_type,struct_member);
    ANSI C++ ANSI C

    DOS UNIX Win16 #include<fcntl.h,io.h>
    OS/2  Win32   int open(const char *path,int access
                [,unsigned mode]);

    DOS UNIX Win16 #include <dirent.h>
    OS/2 Win32    DIR *opendir(char *dirname);

    DOS Win16    #include <conio.h>
             int outp(unsigned portid, int value);

    DOS Win16    #include <dos.h>
             void outport(int portid,int value)
             void outportb(int portid, unsigned char value);

    DOS Win16    #include <conio.h>
             unsigned outpw(unsigned portid,unsigned
             value);

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