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(gcc-300.info)Constant string objects

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Constant string objects
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   GNU Objective-C provides constant string objects that are generated
directly by the compiler.  You declare a constant string object by
prefixing a C constant string with the character `@':

       id myString = @"this is a constant string object";

   The constant string objects are usually instances of the
`NXConstantString' class which is provided by the GNU Objective-C
runtime.  To get the definition of this class you must include the
`objc/NXConstStr.h' header file.

   User defined libraries may want to implement their own constant
string class.  To be able to support them, the GNU Objective-C compiler
provides a new command line options
`-fconstant-string-class=CLASS-NAME'.  The provided class should adhere
to a strict structure, the same as `NXConstantString''s structure:


     @interface NXConstantString : Object
     {
       char *c_string;
       unsigned int len;
     }
     @end

   User class libraries may choose to inherit the customized constant
string class from a different class than `Object'.  There is no
requirement in the methods the constant string class has to implement.

   When a file is compiled with the `-fconstant-string-class' option,
all the constant string objects will be instances of the class specified
as argument to this option.  It is possible to have multiple compilation
units referring to different constant string classes, neither the
compiler nor the linker impose any restrictions in doing this.