io读写

C

#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;

int main()
{
    FILE* f = fopen("a","w");
    fwrite("test",1,strlen("test"),f);
    fclose(f);
    f = fopen("a","r");
    char ch[100];
    memset(ch,0,100);
    fread(ch,1,100,f);
    fclose(f);
    cout << ch << endl;
}

test

输入输出流:istream,ostream
文件输入输出流:ifstream,ofstream.fstream
字符串输入输出流:istringstream,ostringstream,stringstream
ifstream,ofstream,fstream是从istream和ostream中派生出来的，而istream,ostream是从类ios中派生出来的
文件的打开模式：
ios::app:把所有对文件的输出添加成文件尾。它只用于输出文件
ios::binary:文件以二进制方式打。此项缺省时文件以文本方式打开
ios::nocreate:若文件不存在则将导致打开操作失败。
ios::out:表明该文件用于输出，此项可缺省
ios::in：表明该文件用于输入，此项可缺省

#include<iostream>
#include<fstream>
#include<sstream>
#include<istream>
#include<cctype>
using namespace std;

int main()
{
    ifstream in("/home/xiangjie/code/thinking/Test204/a.txt");
    ostringstream os;
    os << in.rdbuf();
    string str = os.str();
    int i=-1;
    while(str[i++]){
        str[i] = toupper(str[i]);
    }
    ofstream of("/home/xiangjie/code/thinking/Test204/b.txt");
    of << os.str();
    of.close();
    in.close();
}

#include<iostream>
#include<fstream>
#include<ostream>
using namespace std;

int main()
{
    int size = 100;
    char buf[size];
    ifstream in("/home/xiangjie/code/thinking/Test204/a.txt");
    ofstream out("/home/xiangjie/code/thinking/Test204/c.txt");
    while(in.getline(buf,size)){
        out << buf << endl;
    }
    out.close();
    in.close();
}

#include<iostream>
#include<string>
#include<vector>
#include<fstream>
#include<stdlib.h>

using namespace std;
static const int SIZE=2;
struct Person{
    string name;
    int age;
    string address;
    string str[SIZE];
    Person(){};
    Person(string n,int a,string ad,string st[SIZE]):name(n),age(a),address(ad)
    {
        for(int i=0;i<SIZE;i++)
            str[i] = st[i];
    };
};

ostream& operator<<(ostream& os,const Person& p)
{
    os << "name:" <<p.name << ",age:" << p.age << ",address" << p.address
            << ",ssn" << p.str[0] << "," << p.str[1];
    return os;
}

class Database{
public:
    size_t sz;
    vector<Person> v;
public:
    Database(size_t s=0):sz(s){};
    size_t query(size_t ssn);
    Person retrieve(size_t rn);
    void add(const Person& p);
};

//ssn美国社保号
size_t Database::query(size_t ssn)
{
    Person p;
    size_t t=0;
    for(int i=0;i<v.size();i++){
        if(atoi(p.str->data())==ssn){
            t = i;
            break;
        }
    }
    return t;
}

Person Database::retrieve(size_t rn)
{
    return v[rn];
}

void Database::add(const Person &p)
{
    v.push_back(p);
}

void read(const Database& db){
    for(int i=0;i<db.v.size();i++){
        cout << "i:" << db.v[i].name << endl;
    }
}

void write(Database& db,Person n)
{
    db.add(n);
}

int main()
{
    string s1[SIZE] = {"abc","def"};
    Person p1(string("zhangsan"),18,string("l1"),s1);
    Database db;
    db.add(p1);
    Person p2(string("lisi"),20,string("l2"),s1);
    write(db,p2);
    read(db);
    cout << p1 << endl;
    ofstream out("/home/xiangjie/code/thinking/Test204/e.txt",ios::app);
    out << p1 << endl;//operator<<
    out.close()//曾经学java的时候有一次忘写了，结果我的D盘出现了一个10G的文件。。。
}