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| 2003/12/11-12 [Computer/SW/Languages/C_Cplusplus, Computer/SW/Compilers] UID:11404 Activity:moderate |
12/10 I am not a programmer so this question may be stupid. What does
@"A string (might be empty)" mean in a gcc?
\_ The '@' character has no meaning other than '@' in standard C. Look
at the documentation for your nonstandard compiler.
\_ What's the meaning of '@' in standard C? I have no C book
near me and I can't find it in the documentation either.
\_ It isn't standard C syntax. If you post a code snippet with
a usage example maybe we can guess what it is.
\_ Sorry I wasn't clear. The '@' is not an operator, token, etc.
It's just another character, like '1' or '8' or '\' and has no
special meaning at all. However, it *does* have a special
meaning in C#. Specifically it means a verbatim string
literal. See:
http://www.softsteel.co.uk/tutorials/cSharp/lesson4.html#3
\_ Please give more context. Otherwise it looks like the program
may be run through a custom pre-processor (@ is expanded to
something else) before being passed to gcc.
\_ What's the source language? Objective-C?
\_ I think @ means something in Objective-C... unicode string maybe?
\_ Apparently an "NSString" object: http://csua.org/u/58b
\_ It means several things in ObjC. @"..." is a way to
create an NSString literal, but it's used in other places,
e.g., @class to predeclare a class name, @interface ... @end
is how you declare a class, etc.
\_ Thanks. Now I realize that the version of documentation
stored on my computer is outdated. It does not define the
@"string" directive even though it is is already in use by
then. Actually it is still not in the grammar section
of the current documentation as far as I see.
http://tinyurl.com/ytlp (developer.apple.com)
\_ What variant of C are you using exactly?
\_ I am reading some Objective C codes for Mac. As there
is no standard whatsoever for Objective C, I should
really say codes for the gcc compiler that comes with
OS X. I am confused why this compiler can
be called gcc: NSString is part of Cocoa, which
is not GPL or open source.
\_ NSString is part of GNUStep which is open src:
http://tinyurl.com/ytlw (gnustep.us)
Also there are some "standards" docs for the
language:
http://pages.cpsc.ucalgary.ca/~burrellm/objc/objc.pdf
\_ It probably should be listed in the grammar, but
you will find it here: http://csua.org/u/58h
This static string syntax, I believe, is an ObjC
thing, and not an Apple extension (GNUStep
as far as I see.
docs refer to it too), but I couldn't test it
it out on soda, as I couldn't find the Foundation
header files. http://csua.org/u/58i |
| 4/3 |
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| www.softsteel.co.uk/tutorials/cSharp/lesson4.html#3 -> www.softsteel.co.uk/tutorials/cSharp/lesson4.html Another variable v can contain a reference to the same object refered to by v. Value Types It is possible in C to define your own value types by declaring enumerators lesson 7 or structs lesson 11 . These user-defined types are mostly treated in exactly the same way as Cs predefined value types, although compilers are optimised for the latter. The following table lists, and gives information about, the predefined value types. New reference types can be defined using class, interface, and delegate declarations covered in lesson 12 . Reference types actually hold the value of a memory address occupied by the object they reference. Consider the following piece of code, in which two variables are given a reference to the same object for the sake of the example, this object is taken to contain the numeric property myValue. Hence, following this piece of code, s1 equals goodbye, whereas s2 still equals hello. The reason for this behaviour is that string objects are immutable. So in order to change what a string variable references, a new string object must be created. Escape Sequences and Verbatim Strings When declaring a string variable, certain characters cant, for various reasons, be included in the usual way. For example, suppose that we want to set variable a to the value: Hello World How are you We could declare this using the following command, which contains escape sequences for the quotation marks and the line break. These are defined by enclosing the required string in the characters and . The only character that needs escaping is the double-quote character, the escape sequence for which is two double-quotes together. For instance, suppose that you want to set the variable text to the following value: the word big contains three letters. Using the verbatim string syntax, the command would look like this: string text the word big contains three letters. Boxing C allows you convert any value type to a corresponding reference type, and to convert the resultant boxed type back again. When the second line executes, an object is initiated as the value of box, and the value held by i is copied across to this object. It is interesting to note that the runtime type of box is returned as the boxed value type; |
| csua.org/u/58b -> developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/ Cocoa: The Objective-C Programming Language This document set is best viewed in a browser that supports frames. |
| tinyurl.com/ytlp -> developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/6objc_grammar/chapter_7_section_1.html Grammar for the Objective-C Language This appendix presents a formal grammar for the Objective-C extensions to the C languageas the Objective-C language is implemented for the Cocoa development environment. It adds to the grammar for ANSI standard C found in Appendix A of The C Programming Language second edition, 1988 by Brian W. Ritchie, published by Prentice Hall, and should be read in conjunction with that book. The Objective-C extensions introduce some new symbols such as class interface , but also make use of symbols such as function definition that are explained in the standard C grammar. Two notational conventions used here differ from those used in The C Programming Language : Literal symbols are shown in code font . Otherwise, this appendix follows the conventions of The C Programming Language . Each part of the grammar consists of a symbol followed by a colon and an indented list of mutually-exclusive possibilities for expanding the symbol. For example: receiver: expression class-name super However, there is an exception: Even though theyre not mutually exclusive, the constituents of classes, categories, and protocols are listed on separate lines to clearly show the ordering of elements. For example: protocol-declaration: protocol protocol-name protocol-reference-list interface-declaration-list end This exception to the general rule is easily recognized since each list terminates with end . There are just four entry points where the Objective-C language modifies the rules defined for standard C: External declarations Type specifiers Type qualifiers Primary expressions This appendix is therefore divided into four sections corresponding to these points. Where a rule in the standard C grammar is modified by an Objective-C extension, the entire rule is repeated in its modified form. Contents: External Declarations Type Specifiers Type Qualifiers Primary Expressions . |
| tinyurl.com/ytlw -> www.gnustep.us/modules.php?op=modload&name=Documentation&file=index&docu=/Foundation/NSString.html The value of opts determines the direction of the search is and whether only leading/trailing occurrances anchored search of replace are substituted. Raises NSInvalidArgumentException if either string argument is nil . Raises NSRangeException if part of searchRange is beyond the end of the receiver. To create a concrete subclass of NSString, you must have your class inherit from NSString and override at least the two primitive methods - length and characterAtIndex: In general the rule is that your subclass must override any initialiser that you want to use with it. The GNUstep implementation relaxes that to say that, you may override only the designated initialiser and the other initialisation methods should work. Lines are delimited by any of these character sequences, the longest CRLF sequence preferred. U000A linefeed U000D carriage return U2028 Unicode line separator U2029 Unicode paragraph separator U000D U000A CRLF The index of the first character of the line at or before aRange is returned in startIndex . The index of the first character of the next line after the line terminator is returned in endIndex. The index of the last character before the line terminator is returned contentsEndIndex . Raises an NSRangeException if the range is invalid, but permits the index arguments to be null pointers in which case no value is returned in that argument. For NSUnicodeStringEncoding and NSUTF8String encoding , a Byte Order Marker if present at the start of the data is removed automatically. If the data is not in a format which can be used internally unmodified, it is copied, otherwise it is used as is. If the data is not copied the flag determines whether the string will free it when it is no longer needed. If the data can not be interpreted using the encoding , the receiver is released and nil is returned. If the receiver does not contain a string representation of a property list then the method returns nil . There are three readable property list storage formats - The binary format used by NSSerializer does not concern us here, but there are two human readable formats, the traditional OpenStep format which is extended in GNUstep and the XML format. If GSMacOSXCompatible is YES then XML property lists are written unless NSWriteOldStylePropertyLists is also YES . By default GNUstep writes old style data and always supports reading of either style. The traditional format is more compact and more easily readable by people, but without the GNUstep extensions cannot represent date and number objects except as strings. The XML format is more verbose and less readable, but can be fed into modern XML tools and thus used to pass data to non-OpenStep applications more readily. The traditional format is strictly ascii encoded, with any unicode characters represented by escape sequences. Both the traditional format and the XML format permit comments to be placed in property list documents. In traditional format the comment notations used in ObjectiveC programming are supported, while in XML format, the standard SGML comment sequences are used. A property list may only be one of the following classes - NSArray An array which is either empty or contains only property list objects. An array is delimited by round brackets and its contents are comma separated there is no comma after the last array element. NSDate Date objects were not traditionally allowed in property lists but were added when the XML format was intoroduced. GNUstep provides an extension to the traditional property list format to support date objects, but older code will not read property lists containing this extension. This format consists of an asterisk follwed by the letter D then a date/time in YYYY-MM-DD HH:MM:SS /-ZZZZ format, all enclosed within angle brackets. This format is a traditional style property list file containing a single dictionary, but with the leading and trailing characters omitted. That is to say, the file contains only semicolon separated key/value pairs and optionally comments. As a convenience, it is possible to omit the equals sign and the value, so an entry consists of a key string followed by a semicolon. In this case, the value for that key is assumed to be an empty string. If aString does not exist in the receiver an empty string is never considered to exist in the receiver, the length of the returned range is zero. If any part of aRange lies outside the range of the receiver, an exception is raised. The options mask may contain the following options - NSCaseInsensitiveSearch NSLiteralSearch NSBackwardsSearch NSAnchoredSearch smallestEncoding - NSStringEncoding smallestEncoding ; So, supplying an index of 3 would return a substring consisting of the entire string apart from the first three character those would be at index 0, 1, and 2. If the supplied index is greater than or equal to the length of the receiver an exception is raised. The compiler generates the instances of this class - which has three instance variables - a pointer to the class this is the sole ivar of NSObject a pointer to the 8-bit data the length of the string In older versions of the compiler, the isa variable is always set to the NXConstantString class. Since GNUstep will generally use the GNUstep extension to the compiler, you should never refer to the constnat string class by name, but should use the NSString constantStringClass method to get the actual class being used for constant strings. What follows is a dummy declaration of the class to keep the compiler happy. The methods in this category are not available in MacOS-X Method summary -immutableProxy immutableProxy - NSString immutableProxy ; Returns a proxy to the receiver which will allow access to the receiver as an NSString, but which will not allow any of the extra NSMutableString methods to be used. You can use this method to provide other code with read-only access to a mutable string you own. Method summary stringWithFormat:arguments: -stringByDeletingPrefix: -stringByDeletingSuffix: -stringByReplacingString:withString: -stringByTrimmingLeadSpaces -stringByTrimmingSpaces -stringByTrimmingTailSpaces stringWithFormat:arguments: id stringWithFormat: NSString format arguments: va_listargList; |
| csua.org/u/58h -> developer.apple.com/documentation/Cocoa/Conceptual/Strings/index.html Cocoa: Strings This document set is best viewed in a browser that supports frames. |
| csua.org/u/58i -> www.gnustep.it/nicola/Tutorials/BasicClasses/node3.html For example, NSString name Nicola; NSString containing a unicode representation of the ASCII string Nicola. A static instance basically means an instance which is allocated at compile time, whose instance variables are fixed, and which can never be released. |
| developer.apple.com Dynamic HTML and XML: The XMLHttpRequest Object Safari now supports the XMLHttpRequest object. Learn how to use it to fetch, store and access XML data for use as web content. Binding Your Preferences in Cocoa Cocoa bindings let developers reuse data in their applications without having to write gluecode. Read this step-by-step article to learn how to use bindings by creating a simple app. Final Cut Pro 4 Opens Up with XML Interchange Format Final Cut Pro can share project information with any application that supports XML Read about the developer opportunities for creating application features and tools. |