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非常容易用错的stringstream

2009-02-26 16:43:33| 分类： C/C++ | 标签： |举报 |字号大中小订阅

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由于C++中的std::string没有提供类似format这样的函数，遇到字符串的格式化一般的替代品是用std::ostringstream。但ostringstream有一些方法非常容易用错：

void clear ( iostate state = goodbit ) 该方法绝非清空ostringstream中的内容，而是清空该流的错误标记！非常容易用错的stringstream - 秒大刀 - 秒大刀的城堡在STL容器里clear方法的含义均为清空容器，但在STL的所有流中clear的含义均为清空错误标记！

void str ( const string & s ) 该方法是重新给ostringstream灌新值的意思。比如oss.str("")将会执行真正的oss清空操作，神奇吧？同理oss.str("Hello")将会使oss中的内容为"Hello"。但注意：oss.str("Hello"); oss << "World";的执行结果将会变成"World"而不是"HelloWorld"，这种功能简直太神奇了，让我活到老学oss到老啊。

不知道世界上有多少程序员曾经为stringstream而愤怒过……

2009-11-25

ostringstream::str签名为：

string str ( ) const; // returns a copy of the string object currently associated with the string stream buffer.
void str ( const string & s ); // copies the content of string s to the string object associated with the string stream buffer. The function effectivelly calls rdbuf()->str(). Notice that setting a new string does not clear the error flags currently set in the stream object unless the member function clear is explicitly called.

项目中经常会用到ostringstream.str()方法，尽量控制不必要的重复调用，这可能会带来性能问题。

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