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| <a name="Containers-1"></a> |
| <h4 class="subsection">10.2.3 Containers</h4> |
| <a name="index-container"></a> |
| <a name="index-list"></a> |
| <a name="index-vector"></a> |
| <a name="index-TREE_005fLIST"></a> |
| <a name="index-TREE_005fVEC"></a> |
| <a name="index-TREE_005fPURPOSE"></a> |
| <a name="index-TREE_005fVALUE"></a> |
| <a name="index-TREE_005fVEC_005fLENGTH"></a> |
| <a name="index-TREE_005fVEC_005fELT"></a> |
| |
| <p>Two common container data structures can be represented directly with |
| tree nodes. A <code>TREE_LIST</code> is a singly linked list containing two |
| trees per node. These are the <code>TREE_PURPOSE</code> and <code>TREE_VALUE</code> |
| of each node. (Often, the <code>TREE_PURPOSE</code> contains some kind of |
| tag, or additional information, while the <code>TREE_VALUE</code> contains the |
| majority of the payload. In other cases, the <code>TREE_PURPOSE</code> is |
| simply <code>NULL_TREE</code>, while in still others both the |
| <code>TREE_PURPOSE</code> and <code>TREE_VALUE</code> are of equal stature.) Given |
| one <code>TREE_LIST</code> node, the next node is found by following the |
| <code>TREE_CHAIN</code>. If the <code>TREE_CHAIN</code> is <code>NULL_TREE</code>, then |
| you have reached the end of the list. |
| </p> |
| <p>A <code>TREE_VEC</code> is a simple vector. The <code>TREE_VEC_LENGTH</code> is an |
| integer (not a tree) giving the number of nodes in the vector. The |
| nodes themselves are accessed using the <code>TREE_VEC_ELT</code> macro, which |
| takes two arguments. The first is the <code>TREE_VEC</code> in question; the |
| second is an integer indicating which element in the vector is desired. |
| The elements are indexed from zero. |
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