流
介绍
// cout: 全局ostream对象，(typedef basic_ostream<char> ostream)
// <<: ostream& ostream::operator<< (string v);
// endl: '\n' + flush
{
ofstream of("MyLog.txt"); //如果文件不存在，新建
of << "Experience is the mother of wisdom" << endl;
of << 234 << endl;
of << 2.3 << endl;
of << bitset<8>(14) << endl; //00001110
of << complex<int>(2, 3) << endl; //(2, 3)
} //RAII
文件流和错误句柄
ofstream of("MyLog.txt"); //清除文件内容
ofstream of("MyLog.txt", ofstream::app); //将输出指针移到文件末尾
of << "Honesty is the best policy." <<endl;
ofstream of("MyLog.txt", ofstream::in | ofstream::out);
of.seekp(10, ios::beg); //将输出指针至文件开头之后的10个字符处
of << "12345"; //覆盖写5个字符
of.seekp(-5, ios::end); //将输出指针移到文件末尾前5个字符处
of.seekp(-5, ios::cur); //将输出指针移到当前位置前5个字符处
ifstream inf("MyLog.txt");
int i;
inf >> i; //读入一个单词, 失败
//错误状态: goodbit, badbit, failbit, eofbit
inf.good(); //一切OK(goodbit == 1)
inf.bad(); //不可恢复的错误(badbit == 1)
inf.fail(); //失败的刘操作，往往可恢复 (failbit == 1, badbit == 1)
inf.eof(); //文件尾(eofbit == 1)
inf.clear(); //清除所有错误状态
inf.clear(ios::badbit); //将错误标志设置一个新值
inf.rdstate(); //读当前状态flag
inf.clear(inf.rdstate() & ~ios::failbit); //只清除failbit位
if (inf) //等效于: if (!inf.fail())
cout << "Read successfully";
inf.exceptions(ios::badbit | ios::failbit); //设置异常mask
//badbit或failbit为1时，抛出ios::failure异常
//eofbit为1时，不抛
inf.exception(ios::goodbit); //不抛异常
格式化数据
cout << 34 << endl; //34
cout.setf(ios::oct, ios::basefield);
cout << 34; //42
cout.setf(ios::showbase);
cout << 34; //042
cout.setf(ios::hex, ios::basefield);
cout << 34; //0x22
cout.unsetf(ios::showbase);
cout << 34; //22
cout.setf(ios::dec, ios::basefiled);
cout.width(10);
cout << 26 << endl; // 26
cout.setf(ios::left, ios::adjustfield); //26
//浮点数
cout.setf(ios::scientific, ios::floatfield);
cout << 340.1 << endl; //3.401000e+002
cout.setf(ios::fixed, ios::floatfield);
cout << 340.1 << endl; //340.100000
cout.precision(3);
cout << 340.1 << endl; /340.100
int i;
cin.setf(ios::hex, ios::basefield);
cin >> i; //Enter: 12
// i==18
ios::fmtflags f = cout.flags();
cout.flags(ios::oct|ios::showbase);
//用来非格式化IO的成员函数
ifstream inf("MyLog.txt");
char buf[80]；
inf.get(buf, 80); //读最多80个字符
Inf.getline(buf, 80); //读最多80个字符，或直到'\n'
inf.read(buf, 20); //读20字符
inf.ignore(3);
inf.peek(); //返回string最顶端的字符
inf.unget(); //将最后一个读的字符放回流中 inf.putback('z');
inf.get(); //读一个字符
inf.gcount(); //返回上次非格式化读的字符数
ofstream of("MyLog.txt");
of.put('c');
of.write(buf, 6); //写buf的前6个字符
of.flush(); //刷新输出
操纵符Manipulators
ostream& endl(ostream& sm) {
sm.put('\n');
sm.flush();
return sm;
}
ostream& ostream::operator<<(ostream& (*func)(ostream&)) {
return (*func)(*this);
}
cout << "Hello" << endl; //endl是函数
cout << ends; // '\0'
cout << flush; //
cin >> ws; //读取并丢弃空白
cout >> setw(8) << left << setfill('_') << 99 << endl; //99______
cout << hex << showbase << 14; //0xe
流缓冲
// 格式化数据 -- 流
// 将数据与外部设备交流 -- 流缓冲
cout << 34;
streambuf* pbuf = cout.rdbuf();
ostream myCout(pbuf);
myCout << 34; // 34输出到标准输出stdout
muCout.setf(ios::showpos); //显示符号
myCout.width(20);
myCout << 12 <<endl; // +12
cout << 12 << endl; //12
适合临时修改数据格式，不想修改cout，可能其他人在用
ofstream of("MyLog.txt");
steambuf* origBuf = cout.rdbuf();
cout.rdbuf(of.rdbuf());
cout << "Hello" << endl; //MyLog.txt has "Hello" 重定向
cout.rdbuf(origBuf);
cout << "Goodbye" << endl; //stdout: Googbye
// 流缓冲迭代器
istreambuf_iterator<char> i(cin);
osteambuf_iterator<char> o(cout);
while (*i != 'x') {
*o = *i;
++o;
++i;
}
copy(istreambuf_iterator<char>(cin), istreambuf_iterator<char>(), ostreambuf_iterator<char>(cout));
字符串流
stringstream ss; // 没有IO操作的流
ss << 89 << "Hex: " << hex << 89 << " Oct: " << oct << 89;
cout << ss.str() << endl; // 89 Hex: 59 Oct: 131
int a, b, c;
string s1;
ss >> hex >> a; //一个token一个token读取，以空格tab和换行分隔，a==137
ss >> s1; // s1: "Hex:"
ss >> dec >> b; // b==59
ss.ignore(6); //忽略接下来6个字符
ss >> oct >> c; // c==89
自定义类中使用流
using namespace std;
struct Dog {
int age_;
string name_;
};
ostream& operator<<(ostream& sm, const Dog& d) {
sm << "My name is " << d.name_ << " and my age is " << d.age_ << endl;
return sm;
}
istream& operator>>(istream& sm, Dog& d){
sm >> d.age_;
sm >> d.name_;
return sm;
}
int main() {
Dog d{2, "Bob"};
cout << d;
cin >> d;
cout << d;
}