使用toupper/tolower函数进行大小写转换

[oracle@jumper oracle]$ man toupper
TOUPPER(3)                 Linux Programmer  Manual                TOUPPER(3)

NAME
       toupper, tolower - convert letter to upper or lower case

SYNOPSIS
       #include 

       int toupper(int c);
       int tolower(int c);

DESCRIPTION
       toupper() converts the letter c to upper case, if possible.

       tolower() converts the letter c to lower case, if possible.

       If  c  is  not  an  unsigned char value, or EOF, the behaviour of these
       functions is undefined.

RETURN VALUE
       The value returned is that of the converted letter, or c if the conver-
       sion was not possible.

CONFORMING TO
       ANSI C, BSD 4.3

BUGS
       The details of what constitutes an uppercase or lowercase letter depend
       on the current locale.  For example, the default "C"  locale  does  not
       know about umlauts, so no conversion is done for them.

       In some non - English locales, there are lowercase letters with no cor-
       responding uppercase equivalent; the German sharp s is one example.

SEE ALSO
       isalpha(3), setlocale(3), locale(7)

GNU                               1993-04-04                        TOUPPER(3)