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_dos_freemem
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─────Run-Time Library───────────────────────────────────────────────────────
 
     The _dos_freemem function uses system call 0x49 to release a
     block of memory previously allocated by _dos_allocmem. The <seg>
     argument is a value returned by a previous _dos_allocmem call. The
     freed memory can no longer be used by the application program.
 
     Return Value
 
     If successful, _dos_freemem returns 0. Otherwise, it returns the
     DOS error code and sets errno to ENOMEM, indicating a bad segment
     value (one that does not correspond to a segment returned by a
     previous _dos_allocmem call) or invalid arena headers.
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