Module std::c_strUnstable
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C-string manipulation and management
This modules provides the basic methods for creating and manipulating null-terminated strings for use with FFI calls (back to C). Most C APIs require that the string being passed to them is null-terminated, and by default rust's string types are not null terminated.
The other problem with translating Rust strings to C strings is that Rust strings can validly contain a null-byte in the middle of the string (0 is a valid Unicode codepoint). This means that not all Rust strings can actually be translated to C strings.
Creation of a C string
A C string is managed through the CString
type defined in this module. It
"owns" the internal buffer of characters and will automatically deallocate the
buffer when the string is dropped. The ToCStr
trait is implemented for &str
and &[u8]
, but the conversions can fail due to some of the limitations
explained above.
This also means that currently whenever a C string is created, an allocation must be performed to place the data elsewhere (the lifetime of the C string is not tied to the lifetime of the original string/data buffer). If C strings are heavily used in applications, then caching may be advisable to prevent unnecessary amounts of allocations.
Be carefull to remember that the memory is managed by C allocator API and not by Rust allocator API. That means that the CString pointers should be freed with C allocator API if you intend to do that on your own, as the behaviour if you free them with Rust's allocator API is not well defined
An example of creating and using a C string would be:
extern crate libc; extern { fn puts(s: *const libc::c_char); } fn main() { let my_string = "Hello, world!"; // Allocate the C string with an explicit local that owns the string. The // `c_buffer` pointer will be deallocated when `my_c_string` goes out of scope. let my_c_string = my_string.to_c_str(); unsafe { puts(my_c_string.as_ptr()); } // Don't save/return the pointer to the C string, the `c_buffer` will be // deallocated when this block returns! my_string.with_c_str(|c_buffer| { unsafe { puts(c_buffer); } }); }extern crate libc; extern { fn puts(s: *const libc::c_char); } fn main() { let my_string = "Hello, world!"; // Allocate the C string with an explicit local that owns the string. The // `c_buffer` pointer will be deallocated when `my_c_string` goes out of scope. let my_c_string = my_string.to_c_str(); unsafe { puts(my_c_string.as_ptr()); } // Don't save/return the pointer to the C string, the `c_buffer` will be // deallocated when this block returns! my_string.with_c_str(|c_buffer| { unsafe { puts(c_buffer); } }); }
Structs
CChars | External iterator for a CString's bytes. |
CString | The representation of a C String. |
Traits
ToCStr | A generic trait for converting a value to a CString. |
Functions
from_c_multistring | Parses a C "multistring", eg windows env values or the req->ptr result in a uv_fs_readdir() call. |