Originální popis anglicky: 
iswupper - test for an uppercase letter wide-character code
Návod, kniha: POSIX Programmer's Manual
#include <wctype.h>
 
 
int iswupper(wint_t 
 wc);
 
The 
iswupper() function shall test whether 
wc is a wide-character
  code representing a character of class 
upper in the program's current
  locale; see the Base Definitions volume of IEEE Std 1003.1-2001,
  Chapter 7, Locale.
The 
wc argument is a 
wint_t, the value of which the application
  shall ensure is a wide-character code corresponding to a valid character in
  the current locale, or equal to the value of the macro WEOF. If the argument
  has any other value, the behavior is undefined.
The 
iswupper() function shall return non-zero if 
wc is an
  uppercase letter wide-character code; otherwise, it shall return 0.
No errors are defined.
The following sections are informative.
None.
To ensure applications portability, especially across natural languages, only
  this function and those listed in the SEE ALSO section should be used for
  classification of wide-character codes.
None.
None.
iswalnum() , 
iswalpha() , 
iswcntrl() , 
iswctype() ,
  
iswdigit() , 
iswgraph() , 
iswlower() , 
iswprint()
  , 
iswpunct() , 
iswspace() , 
iswxdigit() ,
  
setlocale() , the Base Definitions volume of
  IEEE Std 1003.1-2001, Chapter 7, Locale, 
<wchar.h>,
  
<wctype.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
  Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
  Operating System Interface (POSIX), The Open Group Base Specifications Issue
  6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
  Engineers, Inc and The Open Group. In the event of any discrepancy between
  this version and the original IEEE and The Open Group Standard, the original
  IEEE and The Open Group Standard is the referee document. The original
  Standard can be obtained online at http://www.opengroup.org/unix/online.html
  .