C++ file操作

#include <fstream>#include <stdio.h>#include <iostream>#include <string>// not <string.h>#include <stdlib.h>using namespace std;#define MAX_LINE_LEN 100typedef struct people{int sno;char name[20];}stu;struct student{   string name;   int num;   int age;   char sex;};//不同类型文件读写  不同读写方式//追加写数据//如何格式化或者分隔字符串方式从文件中读取数据  //二进制文件读写/*  类          参数的默认方式 ofstream ios::out | ios::trunc // ios::trunc 如果文件已存在则先删除该文件 ifstream ios::in fstream ios::in | ios::out */void readbyline()//使用getline(fstream &fs,string & str)方法，读取文件到str{char buffer[MAX_LINE_LEN];ifstream in("male.txt");if(!in.is_open()){cout<<"open file failed!\n"<<endl;exit(1);}while(!in.eof()){in.getline(buffer,MAX_LINE_LEN);//.....cout<<buffer<<endl;}in.close();}void writefilebystream()//使用插入器(<<) *写*文件{char * name = "d";int position;//ofstream logfile("log.txt");ofstream logfile; logfile.open("log.txt");//默认值为 ios::out | ios::trunc 文件已存在则先删除该文件logfile<<name;  //position=logfile.tellp();//pro1:获取当前文件写指针的位置  写文件的时候 指针前移，再写？cout<<"write pointer:"<<position<<endl;logfile.seekp(position,ios::beg);//设置文件写指针位置  **紧跟刚才的位置写文件**position=logfile.tellp();//获取当前文件写指针的位置cout<<"after seekp,write pointer:"<<position<<endl;logfile<<"good";logfile.close();}void readfilebystream()//使用析取器(>>)读文件{ifstream readfile("log.txt");int position;if(!readfile.is_open()){cout<<"open file failed!\n"<<endl;exit(1);}string name;readfile>>name;position=readfile.tellg();//获取当前文件读指针的位置cout<<"name="<<name<<endl;cout<<"read pointer:"<<position<<endl;readfile.close();}void readbychar()//file2.get(x);表示从文件中读取一个字符，并把读取的字符保存在x中{ifstream readfile("log.txt");char ch = NULL;while(readfile.get(ch))//{cout<<"char is :"<<ch<<endl;//}readfile.close();}void writebychar()//file1.put('c');就是向流写一个字符'c'。 {ofstream out;string name;int i;out.open("log.txt",ios::out|ios::app);//pro3:   (ios::out|ios::app)或(ios:app) |不是||if(!out.is_open()){cout<<"open file failed!\n"<<endl;exit(1);}while(getline(cin,name)&&name.size()>0){out<<name<<endl;//write file}for(i=0;i<5;i++)out.put(i+'0');//write fileout.close();}//二进制文件void writebinary(){ofstream binout("a.dat",ios::binary|ios::out);int num=20;string str("hello world");stu sup_stu={1,"shentan"};//write(const unsigned char *buf,int num);//注意类型转换binout.write((char *)&num,sizeof(num));binout.write((char *)&str,sizeof(str));//写string型数据  不要用str.size()binout.write((char *)&sup_stu,sizeof(sup_stu));binout.close();}void readbinary(){ifstream bin("a.dat",ios::binary|ios::in);int num;string str;stu sup_stu;//read(unsigned char *buf,int num);bin.read((char *)&num,sizeof(num));bin.read((char *)&str,sizeof(str));//读string型  bin.read((char *)&sup_stu,sizeof(sup_stu));cout<<num<<endl;cout<<str<<endl;cout<<sup_stu.sno<<" "<<sup_stu.name<<endl;bin.close();}void writestu(){student stud[3]={"Li",1001,18,'f',"Fun",1002,19,'m',"Wang",1004,17,'f'};ofstream outfile("stud.dat",ios::binary);if(!outfile){cerr<<"open error!"<<endl;exit(1);   }for(int i=0;i<3;i++)outfile.write((char*)&stud[i],sizeof(stud[i]));outfile.close( );}void readstu(){student stud[3];int i;ifstream infile("stud.dat",ios::binary);if(!infile){cerr<<"open error!"<<endl;exit(1);}for(i=0;i<3;i++)infile.read((char*)&stud[i],sizeof(stud[i]));infile.close( );for(i=0;i<3;i++){cout<<"NO."<<i+1<<endl;cout<<"name:"<<stud[i].name<<endl;cout<<"num:"<<stud[i].num<<endl;;cout<<"age:"<<stud[i].age<<endl;cout<<"sex:"<<stud[i].sex<<endl<<endl;}}//格式化方式从文本文件读取数据 C版void FormatRead(){int a,b,c;FILE *fp=fopen("1.txt","r");while(!feof(fp)){fscanf(fp,"%d,%d,%d",&a,&b,&c);//将文件中的1,2,3中的数字读到a b c中cout<<a<<" "<<b<<" "<<c<<endl;}}//格式化方式从文本文件读取数据 C++版int main(){//readbyline();//writefilebystream();//readfilebystream();//readbychar();//writebychar();//二进制文件//writebinary();//readbinary();//writestu();//readstu();//格式化读取文本文件 C版FormatRead();return 0;}