RFC4511 (section 4.5.3.1) shows that if a directory is split over several servers, then the client needs to wade through several redirections in order to get a definitive answer. It seems silly that every client would need to do this. Is there any (free) library that does all of this logic and just returns a GOOD/BAD/UNKNOWN result?
http://linux.die.net/man/3/ldap_set_option
LDAP_OPT_REFERRAL_URLS
Sets/gets an array containing the referral URIs associated to the LDAP handle. outvalue must be a char *, and the caller is responsible of freeing the returned string by calling ldap_memvfree(3), while invalue must be a NULL-terminated char *const *; the library duplicates the corresponding string. This option is OpenLDAP specific.
LDAP_OPT_REFERRALS
Determines whether the library should implicitly chase referrals or not. invalue must be const int *; its value should either be LDAP_OPT_OFF or LDAP_OPT_ON. outvalue must be int *.
Related
I can across a copy methods from charTermAttr from the org.apache.lucene.analysis.tokenattributes.CharTermAttribute library.
Can anyone explain what copyBuffer and buffer does for charTermAttr? The documentation isn't very clear. If you could provide an example that would be great too!
CharTermAttributeImpl keeps internally a char array and a length variable that represents the internal term.
The copyBuffer method writes over this array by using the char array provided with the respective offset and length params.
The buffer method returns the internal array that you can directly modify. Additionally, you can get the term representation as a string by calling the attribute's toString method
Have a look at the javadocs for more details: http://lucene.apache.org/core/4_9_0/core/org/apache/lucene/analysis/tokenattributes/CharTermAttribute.html
I'm using objc_[sg]etAssociatedObject(), and this function uses a memory address as a key. If I pass the same string literal - e.g. "UIImageForTexture" - into the function from two different files, will the two string literals have:
the same memory address?
different memory addresses?
it depends on some other factors.
it's undefined.
I can do this more explicitly by sticking the literal in a file somewhere and referring to it via an extern but I'd like to know if I can avoid having to do that.
This is going to be an implementation defined behavior from the C99 draft standard section 6.4.5 String literals paragraph 6 says:
It is unspecified whether these arrays are distinct provided their elements have the
appropriate values. If the program attempts to modify such an array, the behavior is
undefined.
It's whether two string literals with same content (e.g. char *p1="abc; char *p2="abc";) have the same address or different address is an implementation detail. p1 and p2 may be equal or may not be equal. C standard guarantees neither of them.
So the answer is (3) It depends on the implementation/optimization.
Instead of passing string literals directly, you can use pointers to them and pass them instead. That way, you can reliably handle them and not worry about (1) and (2).
This may be of interest: Addresses of two pointers are same?
I'm trying to get a signature -- either an NSMethodSignature object or at least the type encoding string -- for a method declared in a protocol.
Asking the Protocol object itself isn't possible, since a) it doesn't implement methodSignatureForSelector:, and b) (as noted by Kevin below) it's deprecated.
The runtime function protocol_getMethodDescription returns a struct objc_method_description, which isn't described anywhere in the docs. It's in a public header, though -- <objc/runtime.h>:
struct objc_method_description {
SEL name;
char *types;
};
It seems reasonable to assume that the types string in there is going to be the same kind of signature encoding string used elsewhere, such as that expected by +[NSMethodSignature signatureWithObjCTypes:], and indeed, it looks correct.
What I can't track down is an actual, verifiable connection between that string and the type encoding process.
I can't think what else it would be, but still, do I have any justification for relying on this types string to be valid for interaction with other objects/functions on the same runtime? Note that I'm not writing encoding strings myself or expecting them to have a given format or value -- I only want to pass them from one part of the runtime/framework to another, i.e., retrieve an encoding string from a protocol and a) use it to generate an NSMethodSignature object if one isn't otherwise available, and possibly b) compare it to that of a runtime-generated NSInvocation (i.e., in -forwardInvocation:).
Using Protocol as an object is deprecated. If you check the header <objc/Protocol.h> you'll see that pretty much everything on it is either not available in OBJC-2 or is deprecated as of OS X 10.5. What you can do is use protocol_getMethodDescription(), as you suggested, and pull out the types field. I'm not sure if it's actually officially documented that this is the type encoding of the method, but that is indeed what it is.
I have a C structure that allow users to configure options in an embedded system. Currently the GUI we use for this is custom written for every different version of this configuration structure. What I'd like for is to be able to describe the structure members in some format that can be read by the client configuration application, making it universal across all of our systems.
I've experimented with describing the structure in XML and having the client read the file; this works in most cases except those where some of the fields have inter-dependencies. So the format that I use needs to have a way to specify these; for instance, member A must always be less than or equal to half of member B.
Thanks in advance for your thoughts and suggestions.
EDIT:
After reading the first reply I realized that my question is indeed a little too vague, so here's another attempt:
The embedded system needs to have access to the data as a C struct, running any other language on the processor is not an option. Basically, all I need is a way to define metadata with the structure, this metadata will be downloaded onto flash along with firmware. The client configuration utility will then read the metadata file over RS-232, CAN etc. and populate a window (a tree-view) that the user can then use to edit options.
The XML file that I mentioned tinkering with was doing exactly that, it contained the structure member name, data type, number of elements etc. The location of the member within the XML file implicitly defined its position in the C struct. This file resides on flash and is read by the configuration program; the only thing lacking is a way to define dependencies between structure fields.
The code is generated automatically using MATLAB / Simulink so I do have access to a scripting language to help with the structure creation. For example, if I do end up using XML the structure will only be defined in the XML format and I'll use a script to create the C structure during code generation.
Hope this is clearer.
For the simple case where there is either no relationship or a relationship with a single other field, you could add two fields to the structure: the "other" field number and a pointer to a function that compares the two. Then you'd need to create functions that compared two values and return true or false depending upon whether or not the relationship is met. Well, guess you'd need to create two functions that tested the relationship and the inverse of the relationship (i.e. if field 1 needs to be greater than field 2, then field 2 needs to be less than or equal to field 1). If you need to place more than one restriction on the range, you can store a pointer to a list of function/field pairs.
An alternative is to create a validation function for every field and call it when the field is changed. Obviously this function could be as complex as you wanted but might require more hand coding.
In theory you could generate the validation functions for either of the above techniques from the XML description that you described.
I would have expected you to get some answers by now, but let me see what I can do.
Your question is a bit vague, but it sounds like you want one of
Code generation
An embedded extension language
A hand coded run-time mini language
Code Generation
You say that you are currently hand tooling the configuration code each time you change this. I'm willing to bet that this is a highly repetitive task, so there is no reason that you can't write program to do it for you. Your generator should consume some domain specific language and emit c code and header files which you subsequently build into you application. An example of what I'm talking about here would be GNU gengetopt. There is nothing wrong with the idea of using xml for the input language.
Advantages:
the resulting code can be both fast and compact
there is no need for an interpreter running on the target platform
Disadvantages:
you have to write the generator
changing things requires a recompile
Extension Language
Tcl, python and other languages work well in conjunction with c code, and will allow you to specify the configuration behavior in a dynamic language rather than mucking around with c typing and strings and and and...
Advantages:
dynamic language probably means the configuration code is simpler
change configuration options without recompiling
Disadvantages:
you need the dynamic language running on the target platform
Mini language
You could write your own embedded mini-language.
Advantages:
No need to recompile
Because you write it it will run on your target
Disadvantages:
You have to write it yourself
How much does the struct change from version to version? When I did this kind of thing I hardcoded it into the PC app, which then worked out what the packet meant from the firmware version - but the only changes were usually an extra field added onto the end every couple of months.
I suppose I would use something like the following if I wanted to go down the metadata route.
typedef struct
{
unsigned char field1;
unsigned short field2;
unsigned char a_string[4];
} data;
typedef struct
{
unsigned char name[16];
unsigned char type;
unsigned char min;
unsigned char max;
} field_info;
field_info fields[3];
void init_meta(void)
{
strcpy(fields[0].name, "field1");
fields[0].type = TYPE_UCHAR;
fields[0].min = 1;
fields[0].max = 250;
strcpy(fields[1].name, "field2");
fields[1].type = TYPE_USHORT;
fields[1].min = 0;
fields[1].max = 0xffff;
strcpy(fields[2].name, "a_string");
fields[2].type = TYPE_STRING;
fields[2].min = 0 // n/a
fields[2].max = 0 // n/a
}
void send_meta(void)
{
rs232_packet packet;
memcpy(packet.payload, fields, sizeof(fields));
packet.length = sizeof(fields);
send_packet(packet);
}
Check out this quote from here, towards the bottom of the page. (I believe the quoted comment about consts apply to invariants as well)
Enumerations differ from consts in that they do not consume any space
in the final outputted object/library/executable, whereas consts do.
So apparently value1 will bloat the executable, while value2 is treated as a literal and doesn't appear in the object file.
const int value1 = 0xBAD;
enum int value2 = 42;
Back in C++ I always assumed this was for legacy reasons, and old compilers that couldn't optimize away constants. But if this is still true in D, there must be a deeper reason behind this. Anyone know why?
Just like in C++, an enum in D seems to be a "conserved integer literal" (edit: amazing, D2 even supports floats and strings). Its enumerators have no location. They are just immaterial as values without identity.
Placing enum is new in D2. It first defines a new variable. It is not an lvalue (so you also cannot take its address). An
enum int a = 10; // new in D2
Is like
enum : int { a = 10 }
If i can trust my poor D knowledge. So, a in here is not an lvalue (no location and you can't take its address). A const, however, has an address. If you have a global (not sure whether this is the right D terminology) const variable, the compiler usually can't optimize it away, because it doesn't know what modules can access that variable or could take its address. So it has to allocate storage for it.
I think if you have a local const, the compiler can still optimize it away just as in C++, because the compiler knows by looking at its scope whether or not anyone is interested in its address or whether everyone just takes its value.
Your actual question; why enum/const is the same in D as in C++; seems to be unanswered. Sadly there exists no good reason for this choice whatsoever. I believe that this was just an unintentional side effect in C++ that became a de facto pattern. In D the same pattern was needed, and Walter Bright decided that it should be done as in C++ such that those coming from that place would recognize what to do ... In fact, before this rather IMHO silly decision, the keyword manifest was used instead of enum for this usecase.
I think a good compiler/linker should still remove the constant. It's just that with the enum, it's actually guaranteed in the spec. The difference is primarily a matter of semantics. (Also keep in mind that 2.0 isn't complete yet)
The real purpose of enum being expanded syntactically to support single manifest constants, from what I understand, is that Don Clugston, a D template guru, was doing some crazy stuff with templates. He kept running into long build times, ridiculous compiler memory usage, etc. because the compiler kept creating internal data strucutres for const variables. One key thing about const/immutable variables compared to enums is that const/immutable variables are lvalues and can have their address taken. This means there is some extra overhead for the compiler. This usually doesn't matter, but when you're executing really complicated compile-time metaprograms, even if const variables are optimized away, this is still significant overhead at compile time.
It sounds like the enum value will be used "inline" in expressions where as the const will actually take storage and any expression referencing it will be loading the value from the memory storage.
This sound similar to the difference between const vs. readonly in C#. The former is a compile-time constant and the later is a run-time constant. This definitely affected versioning of assemblies (since assemblies referencing a readonly would receive a copy at compile time and would not get a change to the value if the referenced assembly was rebuilt with a different value).