迭代器是对指针进行进一步抽象的产物。
迭代器是遍历所有容器（序列）/流的统一界面，是标准库泛形算法的基础。
迭代器根据其能力分为五种：
| category | properties | valid expressions | |||
|---|---|---|---|---|---|
| all categories | copy-constructible, copy-assignable and destructible | X b(a); |
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| Can be incremented | ++a |
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| Random Access | Bidirectional | Forward | Input | Supports equality/inequality comparisons | a == b |
| Can be dereferenced as an rvalue | *a a->m |
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| Output | Can be dereferenced as an lvalue (only for mutable iterator types) |
*a = t *a++ = t |
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| default-constructible | X a; X() |
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Multi-pass: neither dereferencing nor incrementing affects dereferenceability Multi-pass是指，迭代器不管进行多少次自增及解引用，都不会使得其指过的对象无法访问。 |
{ b=a; *a++; *b; } |
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| Can be decremented | --a a-- *a-- |
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| Supports arithmetic operators + and - | a + n n + a a - n a - b |
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| Supports inequality comparisons (<, >, <= and >=) between iterators | a < b a > b a <= b a >= b |
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| Supports compound assignment operations += and -= | a += n a -= n |
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| Supports offset dereference operator ([]) | a[n] |
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原文：http://www.cnblogs.com/vsuu/p/4314427.html