Thread: Character Array Help

Hello all, I've encountered something that obviously should not happen in C. I declared an array of characters of say length 10 and insert 12 characters into it and it works fine. Why does this happen?

Code:

#include <stdio.h>

char *myStrCpy(char*, char*);

int main()
{
	char string[] = "Mary had a lamb.";
	char copy[10] = "012345678";
	
	*myStrCpy( copy, string );
	printf("%s\n", copy);
}

char *myStrCpy( char dest[], char source[] )
{
	int i = 0;
	while ( source[i] != '\0' )
	{
		dest[i] = source[i];
		i++;
	}
	dest[i] = '\0';
	return dest;
}

Undefined behavior - Wikipedia, the free encyclopedia

Originally Posted by edishuman

Hello all, I've encountered something that obviously should not happen in C. I declared an array of characters of say length 10 and insert 12 characters into it and it works fine. Why does this happen?

It happens because unlike Java and C#... C has *absolutely no runtime error checking*.

You tell it to do something wrong and it will happily do it without even the first complaint. It's up to you as a programmer to build safeguards into your code to make sure this cannot happen.

(Yeah, I know... WTF???? ... well, that's the way it is.)