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0712-----C++Primer听课笔记----------IO流

2024-07-11 19:42:59   228人阅读

0.不要试着从C++编译器的角度理解问题，而是从程序的语义着手。

1.控制台标准输入输出流的使用

1.1IO对象不可复制或者赋值。因此使用IO对象做参数必须使用非const 引用参数（非const因为对IO对象的读写会改变其状态）。

1.2当cin输入非法数据时，fail置为1，当cin遇到文件结尾（ctrl+D）时， fail和eof都为1。

#include <iostream>#include <string>#include <vector>using namespace std;/* *num是int型，当输入字符串时 cin >> num  会失败 * 这种情况下会对num做一个初始化的操作,并且之后cin也不可用 */int main(int argc, const char *argv[]){    int num;    cin >> num ;    cout << num << endl;    cout << "cin.good = " << cin.good() << endl;    cout << "cin.bad = " << cin.bad() << endl;    cout << "cin.eof = " << cin.eof() << endl;    cout << "cin.fail = " << cin.fail() << endl;    cout  << "-------------------"  << endl;    string s;    cin  >> s;    cout << s << endl;    cout << "cin.good = " << cin.good() << endl;    cout << "cin.bad = " << cin.bad() << endl;    cout << "cin.eof = " << cin.eof() << endl;    cout << "cin.fail = " << cin.fail() << endl;    return 0;}

1.3对于cin 可用的时候为TRUE， 不可用的时候为FALSE。

#include <iostream>#include <string>#include <vector>#include <fstream>#include <stdexcept>using namespace std;/* *文件流对象可用时为true 不可用时为false */ifstream & open_file(ifstream &is, const string &file){    is.close();    is.clear();    is.open(file.c_str());    return is;}int main(int argc, const char *argv[]){    ifstream is;    string filename("a.txt");    if(!open_file(is, filename)){        throw std::runtime_error("file open filed!");    }    is.close();    return 0;}

2.文件流的运用

2.1 ifstream  输入文件流（注意这里的输入输出是相对于程序来说的）

2.1.1 读一行显示到终端

#include <iostream>#include <string>#include <vector>#include <fstream>using namespace std;/* *每次从文件中读一行 然后输出到屏幕 */int main(int argc, const char *argv[]){    ifstream is;    is.open("a.txt");    string line;    while(getline(is, line)){        cout << line << endl;    }    is.close(); //文件流最后要关闭    return 0;}

2.1.2 每次读一个单词 存入vector容器中

#include <string>#include <vector>#include <fstream>using namespace std;/* *读取文件中的单词 并存储到vector容器中 */int main(int argc, const char *argv[]){    string filename = "a.txt";    ifstream is;    is.open(filename.c_str());    vector<string> vec;    string word;    while(is >> word){        vec.push_back(word);    }    is.close();    cout << "word_num = " << vec.size() << endl;    for(vector<string>::iterator it = vec.begin(); it != vec.end(); ++it){        cout << *it << " ";    }    cout << endl;    return 0;}

2.2 ostream  输出文件流

2.2.2 将vector中存储的字符串 写到文件中

#include <iostream>#include <string>#include <vector>#include <fstream>using namespace std;int main(int argc, const char *argv[]){    ofstream os;    os.open("out.txt");    vector<string> vec;    vec.push_back("hello");    vec.push_back("world");    for(vector<string>::iterator it = vec.begin(); it != vec.end(); ++it){        os << *it << endl;    }    os.close();    return 0;}

1.2.3 将一个文件的内容拷贝到另外一个文件中去

#include <iostream>#include <string>#include <vector>#include <fstream>using namespace std;int main(int argc, const char *argv[]){    ifstream is;    ofstream os;    is.open("a.txt");    os.open("b.txt");    string line;    while(getline(is, line) ){        os << line << endl;    }    os.close();    is.close();    return 0;}

3.字符串流

3.1 从文件中读一行存到vector中后，并把一行中的单词存到另一个vector中。

#include <iostream>#include <string>#include <vector>#include <sstream>#include <fstream>using namespace std;int main(int argc, const char *argv[]){    ifstream is;    vector<string> lines, words;    is.open("a.txt");    istringstream ss;    string line, word;    while(getline(is, line)){        lines.push_back(line);        ss.str(line); //        while(ss >> word){            words.push_back(word);        }       ss.clear();    }    is.close();    for(vector<string>::iterator it = lines.begin(); it != lines.end(); ++it){        cout << *it << endl;    }    cout << "------------------------" << endl;    for(vector<string>::iterator it = words.begin(); it != words.end(); ++it){        cout << *it << " ";    }    cout << endl;    return 0;}


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