遍历vector最简洁的方法是通过迭代器:

for (auto it = begin (vector); it != end (vector); ++it) {
    it->doSomething ();
}

或(相当于上述)

for (auto & element : vector) {
    element.doSomething ();
}

在c++ 0x之前，必须将auto替换为迭代器类型，并使用成员函数而不是全局函数begin和end。

This probably is what you have seen. Compared to the approach you mention, the advantage is that you do not heavily depend on the type of vector. If you change vector to a different "collection-type" class, your code will probably still work. You can, however, do something similar in Java as well. There is not much difference conceptually; C++, however, uses templates to implement this (as compared to generics in Java); hence the approach will work for all types for which begin and end functions are defined, even for non-class types such as static arrays. See here: How does the range-based for work for plain arrays?

在STL中，程序员使用迭代器遍历容器，因为迭代器是一个抽象概念，在所有标准容器中实现。例如，std::list根本没有操作符[]。

有什么原因让我在c++中看不到这个吗?这是不好的做法吗?

不。这不是一个不好的实践，但是下面的方法使您的代码具有一定的灵活性。

通常，在c++ 11之前，迭代容器元素的代码使用迭代器，类似于:

std::vector<int>::iterator it = vector.begin();

这是因为它使代码更加灵活。

所有标准库容器都支持并提供迭代器。如果在开发的后期需要切换到另一个容器，则不需要更改此代码。

注意:编写适用于所有可能的标准库容器的代码并不像看起来那么容易。

正确的做法是:

for(std::vector<T>::iterator it = v.begin(); it != v.end(); ++it) {
    it->doSomething();
 }

其中T是向量中类的类型。例如，如果类是CActivity，只需写CActivity而不是T。

这种类型的方法将适用于每个STL(不仅仅是向量，这是更好的一点)。

如果你仍然想使用索引，方法是:

for(std::vector<T>::size_type i = 0; i != v.size(); i++) {
    v[i].doSomething();
}

在vector上迭代并打印其值的正确方法如下:

#include<vector>

// declare the vector of type int
vector<int> v;

// insert elements in the vector
for (unsigned int i = 0; i < 5; ++i){
    v.push_back(i);
}

// print those elements
for (auto it = v.begin(); it != v.end(); ++it){
    std::cout << *it << std::endl;
}

但至少在目前的情况下，使用基于范围的for循环会更好: 对于(auto x: v) std::cout << x << "\n"; (你也可以在auto后面加上&，使x成为对元素的引用，而不是它们的副本。它与上面的基于迭代器的方法非常相似，但更易于读写。)

遍历vector最简洁的方法是通过迭代器:

for (auto it = begin (vector); it != end (vector); ++it) {
    it->doSomething ();
}

或(相当于上述)

for (auto & element : vector) {
    element.doSomething ();
}

在c++ 0x之前，必须将auto替换为迭代器类型，并使用成员函数而不是全局函数begin和end。

This probably is what you have seen. Compared to the approach you mention, the advantage is that you do not heavily depend on the type of vector. If you change vector to a different "collection-type" class, your code will probably still work. You can, however, do something similar in Java as well. There is not much difference conceptually; C++, however, uses templates to implement this (as compared to generics in Java); hence the approach will work for all types for which begin and end functions are defined, even for non-class types such as static arrays. See here: How does the range-based for work for plain arrays?