ZLib does not provide a function that returns the error message corresponding to a specific error code;. This is a typical implementation of the non-throwing message overload. Note that message is allowed to return something different from buffer , which means that we can return character literals directly, without copying them into the supplied buffer first. This allows our function to return the correct message text even when the buffer is too small.
Finally, we need to implement failed , in order to override its default behavior of returning true for all nonzero values:. We can stop here, as this covers everything we set out to do, but we can take an extra step and enable source locations for our error codes. Define a helper macro to avoid the boilerplate of defining the static constexpr source location object each time:. We notice that some of the ZLib error codes correspond to portable errno conditions. Since we have a simple one to one mapping, the former will suffice:.
We can see that we need to define five error codes of our own. This is however not enough; we still need to define the error category for our enumerators, and associate them with it. As we know, Boost. All of the libmyimg::error error codes we have so far represent the same error condition - invalid or unsupported image format.
It might make sense to enable testing for this condition without the need to enumerate all five specific codes. To do this, we can define an error condition enumeration type:. This saves some typing, but a better practice is to use a separate category for the error conditions. System is now header-only. A stub library is still built for compatibility, but linking to it is no longer necessary.
This is a potentially breaking change but its impact is expected to be limited. A virtual function failed has been added, allowing categories for which success is not synonymous with 0. In addition to enabling use in constant expressions and constexpr functions , this significantly improves the quality of the generated code.
As a result of this change, however, now using Boost. System, directly or through a dependency such as Boost. Many of the detailed design decisions were driven by the requirements that users to be able to add additional error categories, and that it be no more difficult to write portable code than system-specific code. It is also useful in its own right. These features are bound to eventually disappear. In the process of adding Boost.
To ease transition, Boost. This allows the creation of generic error codes, an operation typically useful when a function needs to signal a generic failure that does not come from an underlying API, such as for instance an out of memory condition:.
Since equivalence for categories that do not have an identifier is based on comparing object addresses, a user-defined derived category of type C that uses this constructor should ensure that only one object of type C exists in the program. User-defined derived categories that use this constructor are considered equivalent when their identifiers match. Therefore, those categories may have more than one instance existing in a program, but to minimize the possibility of collision, their identifiers must be randomly chosen at the time the category is implemented, not at runtime.
In derived classes, an error condition corresponding to ev. The returned error condition will typically come from the generic category.
If len is 0, nothing is copied, but the function still returns buffer. Note that when len is 0, buffer may be nullptr. The default implementation calls message ev and copies the result into buffer , truncating it to len-1 characters and storing a null terminator. If len is 0, copies nothing. Returns buffer. If message ev throws an exception, the string "Message text unavailable" is used. Turns out to be a race condition in the protocol implementation.
If the initial message is not accepted, the socket is closed by the remote side. The local side did check this after sending the initial message. However, after moving to async operations, the socket check was done after the async write returned locally, and before the async read. There's no way to predict exactly when the remote side will close the socket, you can't wait for that. The only thing you know is that if you receive those 8 bytes, it didn't close the socket.
So the EOF result while reading asynchronously is something that I just have to handle. And I suspect the existing synchronous code may have similar timing issues that haven't surfaced yet :. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
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The type must support the b SyncReadStream concept. This is both an input and an output parameter; on entry, any data in the dynamic buffer's input sequence will be given to the parser first. The function call always returns immediately. The program must ensure that the stream performs no other reads until this operation completes. The implementation may read additional octets that lie past the end of the object being parsed.
Returns: An iterator for the first present element in the traversal list above. If no elements are present, the end iterator. Several member functions from previous versions of class path have been deprecated, either because they have been renamed or because the functionality is no longer desirable or has become obsolete.
Effects: lhs. Returns: true if the sequence of native strings for the elements defined by the range [first1,last1 is lexicographically less than the sequence of native strings for the elements defined by the range [first2,last2. Returns false otherwise. Remarks: If two sequences have the same number of elements and their corresponding elements are equivalent, then neither sequence is lexicographically less than the other.
If one sequence is a prefix of the other, then the shorter sequence is lexicographically less than the longer sequence. Otherwise, the lexicographical comparison of the sequences yields the same result as the comparison of the first corresponding pair of elements that are not equivalent.
Equivalence is determined by the equivalent non-member function, which determines if two paths resolve to the same file system entity. Thus equivalent "foo", "bar" will be true when both paths resolve to the same file.
Programmers wishing to determine if two paths are "the same" must decide if "the same" means "the same representation" or "resolve to the same actual file", and choose the appropriate function accordingly. The inserter and extractor delimit the string with double-quotes " to ensure that paths with embedded spaces will round trip correctly. Returns: os. Returns: is. Returns: Reference to copy of p1 stored by the constructor, or, if none, an empty path.
Returns: Reference to copy of p2 stored by the constructor, or, if none, an empty path. The exact format is unspecified.
Implementations are encouraged but not required to include path1. Caching such status information can result is significant time savings. Cached and non-cached results may differ in the presence of race conditions. Actual cold-boot timing of iteration over a directory with 15, entries was six seconds for non-cached status queries versus one second for cached status queries. Windows XP, 3. Similar speedups are expected on Linux and BSD-derived systems that provide status as a by-product of directory iteration.
Effects: As if,. If the end of the directory elements is reached, the iterator becomes equal to the end iterator value.
Directory iteration shall not yield directory entries for the current dot and parent dot dot directories. It could be a symbolic link to a non-existent file. Programs recursively walking directory trees for purposes of removing and renaming entries may wish to avoid following symbolic links. Effects: Constructs a iterator representing the first entry in the directory p resolves to, if any; otherwise, the end iterator. This may be necessary to prevent loops on some operating systems.
The internal form of the stored information is unspecified. Operational functions access a file by resolving an object of class path to a particular file in a file hierarchy.
See Error reporting. Postconditions: For the returned path, rp, rp. Throws: If base. Otherwise, t he contents and attributes of the file from resolves to are copied to the file to resolves to. Requires: p. Returns: The value of! Returns: true if a new directory was created, otherwise false. Some file systems do not support hard links regardless of the operating system - the FAT system used on floppy discs, memory cards and flash drives, for example.
Some file systems limit the number of links per file.
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