c++: stringstream的使用

使用stringstream需引用头文件< sstream>.

常用方法:

1. string str() const;
   void str(const string& s);
   第一种调用以string形式返回当前流内容的备份.
   第二种调用则抛弃所有之前的内容, 将s内容作为当前流内容.
2. iostate rdstate() const;
   返回当前流内部的错误状态标识(error state flags).
3. void clear(iostate state = goodbit);
   设置错误状态标识(error state flags), 默认为0(goodbit).

注意事项:

1. 若当前流的state不为0(goodbit), 则读取或写入都会失败.
2. clear()方法仅能清除error state flags, 对流内容没有影响.
3. str(const string& s)方法可以设置流内容, 但不影响error state flags.
4. seekg()在C++11和C++98两种标准中有不同的实现, 最好手动clear()保证功能统一.
5. 根据stream去理解stringstream, 而不要根据stl.

示例代码:

#include <sstream>#include <iostream>using namespace std;// cplusplus reference url:// http://www.cplusplus.com/reference/sstream/stringstream/// http://www.cplusplus.com/reference/ios/ios/rdstate/void main(){    stringstream stream;    int n1, n2, n3;    cout << "1. if stringstream state flag is not zero, " << endl         << "   stringstream can not accept input stream." << endl;    stream << "123"; // success, input first num.    cout << stream.rdstate() << " "         << stream.str() << endl;    stream >> n1; // success, output first num. state is set to eofbit.    cout << stream.rdstate() << " "         << stream.eof() << " "         << n1 << " "          << stream.str() << endl;    stream << "789"; // fail, input second num, while state is not 0. state is set to eofbit|badbit.    cout << stream.rdstate() << " "         << stream.eof() << " "          << stream.bad() << " "         << stream.str() << endl;    cout << endl         << "2. clear() can clear state flag, " << endl         << "   but has no effect on actual string buf." << endl;    stream.clear(); // clear state mark.    cout << stream.rdstate() << " "         << stream.eof() << " "         << stream.str() << endl;    stream << "789"; // success, input second num.    cout << stream.rdstate() << " "         << stream.eof() << " "         << stream.str() << endl;    stream >> n2; // success, output second num. state is set to eofbit.    cout << stream.rdstate() << " "         << stream.eof() << " "         << n2 << " "         << stream.str() << endl;    cout << endl         << "3. C++11: seekg() clears the eofbit flag, if set before the call." << endl         << "   C++98: if the eofbit flag is set before the call," << endl         << "          the function fails (sets failbit and returns)" << endl;    stream.seekg(stream.beg);    cout << stream.rdstate() << " "         << stream.eof() << " "         << stream.str() << endl;    stream >> n2; // success, output second num from begining. state is set to eofbit.    cout << stream.rdstate() << " "         << stream.eof() << " "         << n2 << " "         << stream.str() << endl;    cout << endl         << "4. str(&) has no effect on error state flags" << endl;    // stream.clear();    stream.str("456"); // set third num, no change about error state flags.    cout << stream.rdstate() << " "         << stream.eof() << " "         << stream.str() << endl;    stream >> n3; //fail, output third num, while state is not 0. state is set to eofbit|failbit.    cout << stream.rdstate() << " "         << stream.eof() << " "         << stream.fail() << " "         << n3 << " "         << stream.str() << endl;    stream.clear();    stream >> n3; //success, output third num.    cout << stream.rdstate() << " "         << stream.eof() << " "         << n3 << " "         << stream.str() << endl;    cin.get();}