Difference between revisions of "Taglists"
From MorphOS Library
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To be selfdescriptive, every taglist, being just a plain C array, must have some kind of termination. It is very similar to string null-termination idea. The termination is done with a ''TagItem'' having its ''ti_Tag'' set to ''TAG_END'' (which happens to be defined as zero). ''ti_Data'' value of the terminating ''TagItem'' is ignored, it is usually set to zero too. The drawing below shows some simple taglist: | To be selfdescriptive, every taglist, being just a plain C array, must have some kind of termination. It is very similar to string null-termination idea. The termination is done with a ''TagItem'' having its ''ti_Tag'' set to ''TAG_END'' (which happens to be defined as zero). ''ti_Data'' value of the terminating ''TagItem'' is ignored, it is usually set to zero too. The drawing below shows some simple taglist: | ||
| − | [[File:taglists1. | + | [[File:taglists1.png]] |
Revision as of 14:06, 3 November 2010
Grzegorz Kraszewski
A taglist is an array of "key-value" pairs. The key is always a 32-bit integer number and is called a tag. The value has also size of 32 bits. It may be an integer, or a pointer to any structure or object. Taglists are commonly used in the MorphOS API for passing variable number of arguments, usually sets of attributes with their values. A few special key values are used for array termination, concatenation and skipping. A set of functions in the utility.library may be used for taglist traversing, filtering, searching, copying etc.
Every pair in a taglist is a TagItem structure, defined in <utility/tagitem.h>:
struct TagItem
{
ULONG ti_Tag;
ULONG ti_Data;
};
To be selfdescriptive, every taglist, being just a plain C array, must have some kind of termination. It is very similar to string null-termination idea. The termination is done with a TagItem having its ti_Tag set to TAG_END (which happens to be defined as zero). ti_Data value of the terminating TagItem is ignored, it is usually set to zero too. The drawing below shows some simple taglist:
