Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
From time to time, I’ll have an off-by-one error like the following:
unsigned int* x = calloc(2000, sizeof(unsigned int));
printf("%d", x[2000]);
I’ve gone beyond the end of the allocated region, so I get an EXC_BAD_ACCESS signal at runtime. My question is: how is this detected? It seems like this would just silently return garbage, since I’m only off by one byte and not, say, a full page. What part of the system prevents me from just returning the garbage byte at x + 2000?
The memory system has sentinel values at the beginning and end of its memory fields, beyond your allocated bytes. When you free the memory, it checks to see if those values are intact. If not, it tells you.