[darkfox1990]

I'm using Visual C++ 2008 Express. I made the program below but the program runs in an infinite loop (keeps asking for letter and displaying it) for some reason. I thought maybe I messed up the header file or something, so I made a new project and it gives me an error instead, after it shows the intended output. Also, all the other files and headers have the same code in both projects. Changing the "%1s" with "%c" fixes the problem, but why is this happening?

Error says: Debug Error! ... Run-time Check failure#2 - Stack around the variable 'a' was corrupted.

This is the code

#include "stdafx.h"

int _tmain(int argc, _TCHAR* argv[])
{  
	char a;
	printf("Enter letter: ");
	scanf("%1s", &a);
	printf("letter: %c\n",a);
	return 0;
}

[JackOfAllTrades]

You're corrupting your stack. You're using %s in scanf to read into a single character. Try using %c instead.
EDIT: Reading fail...note to self: don't just look at the code.

a is a location on the stack for a single character. By telling scanf you're reading a string, it's going to add a null terminator after the character it reads, which overwrites the byte right after location of a, causing stack corruption.

If warnings were turned up in the compiler, there likely would have been one issued.

[darkfox1990]

Sorry I forgot to mention that I'm learning from a book in which they use the method above. Is the book wrong then?

Edit: Oh yeah, it adds the null terminator. But why isn't it giving that error in the first project. And why is the book using this method as an example (more than one place). Would this work with a C compiler? Thanks a lot.

This post has been edited by darkfox1990: 28 September 2009 - 10:02 AM

[JackOfAllTrades]

That's how they read a single character? What book is this???

[Elcric]

Hi,

This does not have anything to do with your infinite loop, but I think scanf has been replaced with scanf_s

[poncho4all]

Maybe this can help brought to you be MSDN
In the case of characters, one may read a single character as follows:

char c;

scanf("%c", &c, 1);

When reading multiple characters for non-null terminated strings, integers are used as the width specification and the buffer size.

char c[4];

scanf("%4c", &c, 4); // not null terminated

You can see more info here
http://msdn.microsof...8et(VS.80).aspx