C++ 获取 std::string 的最后一个元素
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Get the last element of a std::string
提问by Deve
I was wondering if there's an abbreviation or a more elegant way of getting the last character of a string like in:
我想知道是否有缩写或更优雅的方式来获取字符串的最后一个字符，例如：
char lastChar = myString.at( myString.length() - 1 );
Something like myString.back()doesn't seem to exist. Is there an equivalent?
类似的东西myString.back()似乎不存在。有等价物吗？
回答by templatetypedef
In C++11 and beyond, you can use the backmember function:
在 C++11 及更高版本中，您可以使用back成员函数：
char ch = myStr.back();
In C++03, std::string::backis not available due to an oversight, but you can get around this by dereferencing the reverse_iteratoryou get back from rbegin:
在 C++03 中，std::string::back由于疏忽而不可用，但您可以通过取消引用reverse_iterator您从rbegin以下位置返回的来解决此问题：
char ch = *myStr.rbegin();
In both cases, be careful to make sure the string actually has at least one character in it! Otherwise, you'll get undefined behavior, which is a Bad Thing.
在这两种情况下，请注意确保字符串中至少包含一个字符！否则，你会得到undefined behavior，这是一件坏事。
Hope this helps!
希望这可以帮助！
回答by Kerri Brown
You probably want to check the length of the string first and do something like this:
您可能想先检查字符串的长度并执行如下操作：
if (!myStr.empty())
{
char lastChar = *myStr.rbegin();
}
回答by fredoverflow
You could write a function template backthat delegates to the member function for ordinary containers and a normal function that implements the missing functionality for strings:
您可以编写一个函数模板back，委托给普通容器的成员函数和一个实现字符串缺失功能的普通函数：
template <typename C>
typename C::reference back(C& container)
{
return container.back();
}
template <typename C>
typename C::const_reference back(const C& container)
{
return container.back();
}
char& back(std::string& str)
{
return *(str.end() - 1);
}
char back(const std::string& str)
{
return *(str.end() - 1);
}
Then you can just say back(foo)without worrying whether foois a string or a vector.
然后你可以直接说back(foo)而不用担心foo是字符串还是向量。
回答by tenpn
*(myString.end() - 1)maybe? That's not exactly elegant either.
*(myString.end() - 1)也许？这也不是很优雅。
A python-esque myString.at(-1)would be asking too much of an already-bloated class.
python-esquemyString.at(-1)会要求太多已经臃肿的类。
