C Strings

C and C++ strings are byte strings: programs manipulate individual bytes and the contents need not be valid UTF-8, so strings are translated as u8 buffers rather than Rust String values. A string literal becomes a per-thread interned buffer with a trailing zero byte, handed out as a Ptr<u8> by Ptr::from_string_literal. Ptr<u8> also carries the memory functions C strings rely on: memcpy (with memmove semantics for overlapping buffers instead of undefined behavior), memset, memcmp, and to_rust_string for crossing into Rust APIs.

CStringIterator, returned by to_c_string_iterator, walks the bytes of a Ptr<u8> up to the null terminator; the string.h rules are built on it, and Display for Ptr<u8> prints it, so a C string can be formatted directly.

Copying a string does not go through the iterator, which would grow its destination as it goes. with_c_str scans for the null terminator in the backing storage and lends the bytes to a closure, so measuring or borrowing a string allocates nothing (c_str_len, and count on a CStringIterator, are built on it). to_c_bytes and to_rust_string, and through them strdup and the std::string constructors, copy the string with a single allocation. to_c_bytes leaves room for one more byte, which callers usually spend on the terminator or a newline.

Iterating a Ptr<T> reports how many elements are left, so collecting a Ptr into a Vec also allocates once.