Fix for isalpha() assertions (Almost identical to revision 29924's fix). Added the rationale for this fix in comments so hopefully this won't happen a third time at the same point in code ;).

svn-id: r30531

1 files changed, 13 insertions, 1 deletions

diff --git a/engines/agi/agi.cpp b/engines/agi/agi.cpp
index 17359236f0..5cf82b83bd 100644
--- a/engines/agi/agi.cpp
+++ b/engines/agi/agi.cpp
@@ -222,7 +222,19 @@ void AgiEngine::processEvents() {
 				// Not a special key, so get the ASCII code for it
 				key = event.kbd.ascii;
 
-				if (isalpha(key)) {			
+				// Function isalpha is defined in <ctype.h> so the following applies to it:
+				//
+				// The C Programming Language Standard states:
+				//   The header <ctype.h> declares several functions useful for classifying
+				//   and mapping characters. In all cases the argument is an int, the value
+				//   of which shall be representable as an unsigned char or shall equal the
+				//   value of the macro EOF. If the argument has any other value, the
+				//   behavior is undefined.
+				//
+				// For a concrete example (e.g. in Microsoft Visual Studio 2003):
+				//   When used with a debug CRT library, isalpha will display a CRT assert
+				//   if passed a parameter that isn't EOF or in the range of 0 through 0xFF.
+				if (key >= 0 && key <= 0xFF && isalpha(key)) {
 					// Key is A-Z. 
 					// Map Ctrl-A to 1, Ctrl-B to 2, etc.
 					if (event.kbd.flags & Common::KBD_CTRL) {