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     The sopen function opens the file specified by <filename> and
     prepares the file for subsequent shared reading or writing, as
     defined by <oflag> and <shflag>.
 
     The integer expression <oflag> is formed by combining one or more
     of the following manifest constants (defined in FCNTL.H). (When
     more than one manifest constant is given, the constants are joined
     with the OR operator (|).)
 
     O_APPEND     O_EXCL       O_TEXT
     O_BINARY     O_RDONLY     O_TRUNC
     O_CREAT      O_RDWR       O_WRONLY
 
     The <shflag> argument is a constant expression consisting of one
     of the following manifest constants (defined in SHARE.H):
 
     SH_COMPAT    SH_DENYRW
     SH_DENYNO    SH_DENYWR
     SH_DENYRD
 
     If SHARE.COM (or SHARE.EXE in some versions of MS-DOS) is not
     installed, MS-DOS ignores the sharing mode. (See your system
     documentation for detailed information about sharing modes.)
 
     The sopen function should be used only under OS/2 and MS-DOS
     version 3.0 and later. Under earlier versions of MS-DOS, the
     <shflag> argument is ignored.
 
     The <pmode> argument is required only when O_CREAT is specified.
     If the file does not exist, <pmode> specifies the file's
     permission settings, which are set when the new file is closed for
     the first time. Otherwise, the <pmode> argument is ignored. The
     <pmode> argument is an integer expression containing one or both
     of the manifest constants S_IWRITE and S_IREAD (defined in
     SYS\STAT.H). When both constants are given, they are combined
     with the OR operator (|).
 
     If write permission is not given, the file is read-only. Under
     DOS and OS/2, all files are readable; it is not possible to
     give write-only permission. Thus, the modes S_IWRITE and
     S_IREAD | S_IWRITE are equivalent.
 
     Note that under MS-DOS versions 3.x with SHARE installed, a
     problem occurs when opening a new file with sopen under the
     following sets of conditions:
 
        ■ With <oflag> set to O_CREAT | O_RDONLY or O_CREAT | O_WRONLY,
          <pmode> set to S_IREAD, and <shflag> set to SH_COMPAT
 
        ■ With <oflag> set to any combination that includes O_FLAG,
          <pmode> set to S_IREAD, and <shflag> set to anything other
          than SH_COMPAT
 
     In either case, the operating system prematurely closes the file
     during system calls made within sopen, or the system generates a
     sharing violation (INT 24H). To avoid the problem, open the file
     with <pmode> set to S_IWRITE. After closing the file, call chmod
     and change the mode back to S_IREAD. Another solution is to
     open the file with <pmode> set to S_IREAD, <oflag> set to
     O_CREAT | O_RDWR, and <shflag> set to SH_COMPAT.
 
     The sopen function applies the current file-permission mask to
     <pmode> before setting the permissions (see umask).
 
     Return Value
 
     The sopen function returns a file handle for the opened file. A
     return value of -1 indicates an error, and errno is set to EACCES,
     EEXIST, EMFILE, or ENOENT.
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