Using __toascii() got me a runtime access violation

[glyfyx]

I'm very rusty - haven't coded C/C++ since 1994 - and I'm sure there's a simple answer, but I can't find it. I'm not using 'string' support. Just the old char* methods, and the code is behaving well except when I tried to convert a keyboard virtual key code to a it's ascii character I got a runtime access violation. The 'break' option showed me the site of the infraction - inside some MS code located in the midst of some UNICODE related logic, judging by the Defines. I included , but it didn't help. The related trimmed code follows: char c; c = (char)__toascii(keyCode); keyCode = p->vkCode; The offending later statement is: nLen = fprintf(fOut,"kcK=%d ud=%s kc=%d sh=%d ti=%d %s\n",cb.kcK,updn,keyCode,Shift,tick, c); The following statement works perfectly (as above, but no c at the end) nLen = fprintf(fOut,"kcK=%d ud=%s kc=%d sh=%d ti=%d %s\n",cb.kcK,updn,keyCode,Shift,tick); Searched the articles and FAQ but didn't find anything. Hope you can give me a hand here. BTW, I want to stay in the char* arena rather than strings, for now. I'm using Visual C++ 2003 and running Win2K SP4 One more thing - I'm logged in under my old email glyfyx@storm.ca but I have a new address, glyfix@storm.ca. I guess I should change it at Code Project? Thanks glyfyx

[Maxwell Chen]

If c is a char, you should use %c. That's all. :-D

Maxwell Chen

[Rajkumar R]

glyfyx wrote:

I tried to convert a keyboard virtual key code to a it's ascii character

if you are converting from Keyboard Virtual KeyCode, use int ToAscii( UINT uVirtKey, UINT uScanCode, PBYTE lpKeyState, LPWORD lpChar, UINT uFlags );

glyfyx wrote:

The offending later statement is: nLen = fprintf(fOut,"kcK=%d ud=%s kc=%d sh=%d ti=%d %s\n",cb.kcK,updn,keyCode,Shift,tick, c);

format specifier is %s and passing char, c.

[Mark Salsbery]

The arguments you pass to fprintf() need to match the format specifiers in the format control string, in both type and number of arguments. All the "%d"s in the format control string need a corresponding 32-bit integer argument passsed... All the "%s"s in the format control string need a corresponding pointer to a null-terminated string passed. The version where you don't pass the c argument  only appears to work, since you pass 5 arguments when the format control string specifies an expected 6 arguments. The version that crashes probably fails because c is a char but the format specifier is %s, which means the passed argument should be a pointer to a NULL-terminated string, not a single character. If you do something like this, it should work:

char c[2];
c[0] = (char)__toascii(keyCode);
c[1] = '\0';
keyCode = p->vkCode;
...
nLen = fprintf(fOut,"kcK=%d ud=%s kc=%d sh=%d ti=%d %s\n",cb.kcK,updn,keyCode,Shift,tick, c);

Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[Mark Salsbery]

:doh: I forgot about %c....do you need to cast the c argument to an int when it's passed as an argument for %c? I have't used that stuff in a long time :) Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[Maxwell Chen]

Mark Salsbery wrote:

I forgot about %c....do you need to cast the c argument to an int when it's passed as an argument for %c?

No, not needed. Simply this way is fine. :-D

char a = 65;
printf("%c \n", a);
// Result:
// A
// Press any key to exit.

Maxwell Chen

[Mark Salsbery]

Cool thanks! Cheers, Mark

Mark Salsbery Microsoft MVP - Visual C++ :java:

[glyfyx]

Of course, %c for char! I was sure it had a simple answer but couldn't see it for looking - most embarrassing. Too many years of VB? So big thanks Maxwell and Mark! Also Mark, I was starting to think of assembling a 2 byte char array as you suggested - that'd work with %s. Also special thanks to Rajkumar R for the ToAscii suggestion, which is intriguing to say the least, since it requires a GetKeyboardState call to set its 256 byte array arg, lpKeyState, to the current status of *all* the virtual keys. I would have thought GetKeyState for just the virtual key in question (1st arg, uVirtKey),would be sufficient. I suppose ToAscii will be a case-sensitive conversion - will give it a shot and see what happens. int ToAscii( UINT uVirtKey, UINT uScanCode, PBYTE lpKeyState, LPWORD lpChar, UINT uFlags ); Here's the MSDN article... http://msdn2.microsoft.com/en-us/library/ms646299(VS.85).aspx Thanks again everyone! glyfyx