5 ms·

std::vector<whatever> in C++ is safe and is nothing at all like a fixed size array of whatever in C. People who don't understand this are ignorant of the facts.

by w8rbt 9y ago

std::vector<whatever> in C++ is safe and is nothing at all like a fixed size array of whatever in C. People who don't understand this are ignorant of the facts. They are totally different languages. C++ is much safer than C. Go ahead and try to overflow std::vector<whatever>. You can't. It's not possible. Also, it is relatively straight-forward to compile C code with a C++ compiler and adopt C++ constructs while throwing out all the old insecure C constructs. Doing this would vastly improve security and is achievable in a short period of time with little or no performance loss (it will probably run even faster). Yet, all I read about on web forums such as HN are unattainable suggestions such as re-write X in the newest, non-standard, corporate backed/controlled language that isn't nearly as tested nor as performant as ISO Standard C++. Maybe it's just me, but I find these suggestions to be totally out of touch with reality and really uniformed about the vast differences between C and C++.

tonyarkles 9y ago
> std::vector<whatever> in C++ is safe I may be remembering this incorrectly, but vec.at(x) is safe (i.e. does bounds checking), but vec[x] is not safe. I'm going to try some test code here and check, but I'm pretty sure vec[x] will happily overflow. Edit: https://gist.github.com/tonyarkles/e702e4d5b530a9b7cd3fc9837c6609f2 https://gist.github.com/tonyarkles/e702e4d5b530a9b7cd3fc9837... Definitely overflows and segfaults while unwinding the stack (presumably while deallocating the stack-allocated vector)
- w8rbt 9y ago
  You can't overflow a vector. It's not a fixed size array. It grows automatically as needed. What your example shows is an attempt to access a vector element that does not exist (std::out of range). And, that is undefined behavior and is documented. Also, that code is 95% C (not C++). Even the includes and prints are C. Pure, idiomatic C++ would use iostream rather than stdio.h, and a vector iterator to access the elements rather than looping over the vector (in C like fashion) using an integer (which is unrelated to the vector) in an effort to access elements via index.
  - thriftwy 9y ago
    > that is undefined behavior and is documented In C, buffer overruns are undefined behavior and are documented. Back to square 1.
  - cesarb 9y ago
    > You can't overflow a vector. It's not a fixed size array. It grows automatically as needed. His example shows the precise opposite: the vector didn't grow automatically. Instead, memory outside the vector bounds was accessed, i.e., the vector overflowed. Yes, idiomatic modern C++ makes that less likely, by reducing the use of explicit indexes. Even then, you still can overflow a vector with innocent-looking code.
  - spc476 9y ago
    But can the compiler warn about such undefined behavior? Because if it can't, it's not much better than C.
    - tonyarkles 9y ago
      I just tried: g++ -Wall -pedantic vec.cpp And got no errors or warnings.

by w8rbt 9y ago

tonyarkles 9y ago

> std::vector<whatever> in C++ is safe I may be remembering this incorrectly, but vec.at(x) is safe (i.e. does bounds checking), but vec[x] is not safe. I'm going to try some test code here and check, but I'm pretty sure vec[x] will happily overflow. Edit: https://gist.github.com/tonyarkles/e702e4d5b530a9b7cd3fc9837c6609f2 https://gist.github.com/tonyarkles/e702e4d5b530a9b7cd3fc9837... Definitely overflows and segfaults while unwinding the stack (presumably while deallocating the stack-allocated vector)

w8rbt 9y ago
You can't overflow a vector. It's not a fixed size array. It grows automatically as needed. What your example shows is an attempt to access a vector element that does not exist (std::out of range). And, that is undefined behavior and is documented. Also, that code is 95% C (not C++). Even the includes and prints are C. Pure, idiomatic C++ would use iostream rather than stdio.h, and a vector iterator to access the elements rather than looping over the vector (in C like fashion) using an integer (which is unrelated to the vector) in an effort to access elements via index.
- thriftwy 9y ago
  > that is undefined behavior and is documented In C, buffer overruns are undefined behavior and are documented. Back to square 1.
- cesarb 9y ago
  > You can't overflow a vector. It's not a fixed size array. It grows automatically as needed. His example shows the precise opposite: the vector didn't grow automatically. Instead, memory outside the vector bounds was accessed, i.e., the vector overflowed. Yes, idiomatic modern C++ makes that less likely, by reducing the use of explicit indexes. Even then, you still can overflow a vector with innocent-looking code.
- spc476 9y ago
  But can the compiler warn about such undefined behavior? Because if it can't, it's not much better than C.
  - tonyarkles 9y ago
    I just tried: g++ -Wall -pedantic vec.cpp And got no errors or warnings.