C++ string && char * && int之间的关系及转换
最近一直在忙别的事情，没有多少时间来写东西，今天算是抽出一点空闲，聒噪一下最近遇到的问题。
开始之前，说下自己的感触。抽象一下计算机or程序，其实你会感觉很简单，输入，处理，输出。在输入这一块里，基本都是字符类型，所以搞清楚如何处理这种类型的数据很重要。甚至从我一直在学习的python来看，这个道理也非常适用！
不说废话了！string其实是作为C++的一个类存在，我们在声明string str的时候，其实就是声明了一个类的对象。这个类有很多内建函数，例如+(链接字符串的操作)，length()等等。而char是C/C++的一个基本类型，一个关键字(string不是C++的关键字)，char *声明的是一个指针。
因为在使用char *的时候，指针空间大小的分配需要注意，所以string的出现方便了这一系列的问题。至于string如何在char *以及int之间转换，其实也很简单，不过在谈论如何转换前，我们再说下stringstream(流的输入输出操作)，它是C++新增的<sstream>库中定义的其中一个类，还有两个类分别是istringstream(流的输入操作), ostringstream(流的输出操作)。需要注意一点的是，<sstream>使用string对象来代替字符数组，这样可以避免缓冲区溢出的危险，而且，传入参数和目标对象的类型被自动推倒出来，即使使用了不正确的格式化符号也没有危险(但是如果你想多次使用同一个stringstream对象，记得每次使用前使用clear()方法——stringstream对象的构造和析构都非常耗用CPU时间，所以这样重复利用比较好)。
int 转 string：
stringstream ss; string str; int n; ss << n; ss << str;
string转int：
string str; int n = atoi(str.c_str());
string转char *：
string str; char *a = str.c_str();
char *转string：
string str; char *a = "abc"; str(a);//初始化即可
atoi()意思是array to int，而c_str()返回的是pointer，所以这里算是比较好理解把。
PS：推荐一个比较好的C++函数以及库的说明查找网站www.cplusplus.com.
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