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cin支持的类型
也支持 signed char*, char*, unsigned char*
cin连续输入的话会跳过空格, 换行符, 制表符
会再不符合变量类型的输入流前面停止。并且将不符合的字符留在输入流中
#includeint main(){ using namespace std; cout << "Enter numbers: "; int sum = 0; int input; while (cin >> input) { sum += input; } cout << "Last value entered = " << input <
input最后返回的是0 嗯。。。为啥不是-123 难道是将false转换成int型么
流状态
iostate流状态数据成员的数据类型
3个ios_base元素组成: eofbit, badbit, failbit.
都是1位
文件末尾 设置eofbit
未能读取到预期的字符 设置failbit
I/O失败 设置failbit
其他无法判断的失败 设置badbit
设置状态
clear() 默认使用默认参数0 将3个状态位全部设置为0 或者传入特定的状态位排除掉(就是说这个参数不设置为0 其他都设为0)
clear(eofbit)
setstate(),必须制定参数 然后设置该参数位为0
exceptions()
#include#include int main(){ using namespace std; cin.exceptions(ios_base::failbit); cout << "Enter numbers: "; int sum = 0; int input; try { while (cin >> input) sum += input; } catch(ios_base::failure & bf) { cout << bf.what() << endl; cout << "O! the horror!\n"; } cout << "Last value entered = " << input << endl; cout << "Sum = " << sum << endl; return 0;}
异常抛的和书中不一样 嗯。。我不想去管它
其他istream类方法
get()读取下一个字符 转成整形 到文件尾 返回EOF
get(char & c) 转成字符型 跳过空格, 回车键停止
返回istream对象的引用
用哪个?
getline读取到换行符之后会抽出来并丢弃它
cin.ignore() 用来丢弃指定字符前的指定的字符或指定数量的字符
cin.ignore(255, '\n') 丢弃255个字符或达到了第一个换行符前面的所有字符
程序示例
#includeconst int Limit = 255;int main(){ using std::cout; using std::cin; using std::endl; char input[Limit]; cout << "Enter a string for getline() processing:\n"; cin.getline(input, Limit, '#'); cout << "Here is your input:\n"; cout << input << "\nDone with phase 1\n"; char ch; cin.get(ch); cout << "The next input character is " << ch << endl; if (ch != '\n') cin.ignore(Limit, '\n'); cout << "Enter a string for get() processing:\n"; cin.get(input, Limit, '#'); cout << "Here is your input:\n"; cout << input << "\nDone with phase 2\n"; cin.get(ch); cout << "The next input character is " << ch << endl; return 0;}
空行不会阻止getline()设置failbit
读满字符 设置failbit
其他istream方法
read()读取指定数量字符存到指定变量中 。不会转为字符串。也就是说结尾不会加上'\0'
peek()读取下一个字符 但不抽取出来。字符依然在输入流中 用来做判断
gcount()返回最后一个不是通过>>读取的字符数 使用strlen()更快
putback() 将1个字符插到输入字符串中 该字符是吓一跳输入语句读取的第一个字符
#includeint main(){ using std::cout; using std::cin; using std::endl; char ch; while(cin.get(ch)) { if (ch != '#') cout << ch; else {// 将‘#’写到cin输入流开头 cin.putback(ch); break; } } if (!cin.eof()) { cin.get(ch); cout << endl << ch << " is next input character.\n"; } else { cout << "End of file reached.\n"; std::exit(0); } while(cin.peek() != '#') { cin.get(ch); cout << ch; } if (!cin.eof()) { cin.get(ch); cout << endl << ch << " is next input character.\n"; } else cout << "Enter of file reached.\n"; return 0;}
peek()例子
#includeconst int SLEN = 10;inline void eatline() {while (std::cin.get() != '\n') continue;}int main(){ using std::cout; using std::cin; using std::endl; char name[SLEN]; char title[SLEN]; cout << "Enter your name: "; cin.get(name, SLEN);// 检查字符流中当前的字符 if (cin.peek() != '\n') cout << "Sorry, we only have enough room for " << name << endl; eatline(); cout << "Dear " << name << ", enter your title: \n"; cin.get(title, SLEN); if (cin.peek() != '\n') cout << "We were forced to truncate your title.\n"; eatline(); cout <<" Name: " << name << "\nTitle: " << title << endl; return 0;}
cin内容完结 这节也好多内容 都是cin的
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