[diskcontroller] use isalnum

diff --git a/src/lib/elm_diskcontroller.c b/src/lib/elm_diskcontroller.c
index 2ea9766..63d3e63 100644 (file)
--- a/src/lib/elm_diskcontroller.c
+++ b/src/lib/elm_diskcontroller.c
@@ -220,8 +220,7 @@ static int check_letter(const char *str, int length)
        int code = str[length];\r
 \r
        if(code == '\0') return length; // null string\r
-       else if((code >= 'A' && code <= 'Z') || (code >= 'a' && code <= 'z')) return length; // alphabet\r
-       else if ('0'<=code && code<='9') return length; // number\r
+       else if(isalnum(code)) return length; // alphabet or number\r
        else if ((33<=code && code<47) || (58<=code && code<64) || (91<=code && code<96) || (123<=code && code<126)) return length; // special letter\r
 \r
        return length-1;\r