C++文件流读写操作详解

#include <fstream>  
ofstream         //文件写操作 内存写入存储设备   
ifstream         //文件读操作，存储设备读区到内存中  
fstream          //读写操作，对打开的文件可进行读写操作

void open ( const char * filename,  
            iOS_base::openmode mode = ios_base::in | ios_base::out );

void open(const wchar_t *_Filename,
        ios_base::openmode mode= ios_base::in | ios_base::out,
        int prot = ios_base::_Openprot)；

#include <iostream>
#include <fstream>
#include <iomanip>
using namespace std;
 
int main()
{
    ofstream inFile;
    
    inFile.open("inFile.txt",ios::trunc);
 
    int i;
    char a='a';
    for(i=1;i<=26;i++)//将26个数字及英文字母写入文件
    {
        inFile<<setw(2)<<i<<"\t"<<a<<"\n";
        a++;
    }
    inFile.close();//关闭文件
}

// writing on a text file  
 #include <fstream.h>  
 
 int main () 
 {  
     ofstream out(”out.txt”);  
     if (out.is_open())   
    {  
         out << ”This is a line.\n”;  
         out << ”This is another line.\n”;  
         out.close();  
     }  
     return 0;  
 }  
//结果: 在out.txt中写入：  
This is a line.  
This is another line   

// reading a text file  
   #include <iostream.h>  
   #include <fstream.h>  
   #include <stdlib.h>  
     
   int main () 
   {  
       char buffer[256];  
       ifstream in(”test.txt”);  
       if (! in.is_open())  
       { 
       cout << ”Error opening file”; 
       exit (1);
       }  
       while (!in.eof() )  //eof到文件末尾返回true
       {  
           in.getline (buffer,100);  
           cout << buffer << endl;  
       }  
       return 0;  
   }  
   //结果 在屏幕上输出  
    This is a line.  
    This is another line  

#include <iostream>
#include <fstream>
using namespace std;
void testByChar()
{
    fstream testByCharFile;
    char c;
    testByCharFile.open("inFile.txt",ios::in);
    while(!testByCharFile.eof())
    {
        testByCharFile>>c;
        cout<<c;
    }
    testByCharFile.close();
}
void testByLine()
{
    char buffer[256];
    fstream outFile;
    outFile.open("inFile.txt",ios::in);
    cout<<"inFile.txt"<<"--- all file is as follows:---"<<endl;
    while(!outFile.eof())
    {
        outFile.getline(buffer,256,'\n');//getline(char *,int,char) 表现该行字符达到256个或碰到换行就结束
        cout<<buffer<<endl;
    }
    outFile.close();
}
int main()
{
   cout<<endl<<"逐个字符的读取文件：testByChar() "<<endl<<endl;
   testByChar();
   cout<<endl<<"将文件每行内容存储到字符串中，再输出字符串 ：testByLine()"<<endl<<endl;
   testByLine();
}

//如何统计文本的行数及如何读取文件某一行内容：
 
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
 
int CountLines(char *filename)
{
    ifstream in;
    int n=0;
    string tmp;
    in.open(filename,ios::in);//ios::in 表示以只读的方式读取文件
    if(in.fail())//文件打开失败:返回0
    {
        return 0;
    }
    else//文件存在
    {
        while(getline(in,tmp,'\n'))
        {
            n++;
        }
        in.close();
        return n;
    }
}
 
string ReadLine(char *filename,int line)
{
    int lines,i=0;
    string temp;
    fstream file;
    file.open(filename,ios::in);
    lines=CountLines(filename);
 
    if(line<=0)
        return "Error 1: 行数错误，不能为0或负数。";
    if(file.fail())
        return "Error 2: 文件不存在。";
    if(line>lines)
        return "Error 3: 行数超出文件长度。";
    
    while(getline(file,temp)&&i<line-1)
    {
        i++;
    }
    file.close();
    return temp;
}

int main()
{
    int line;
    char filename[]="inFile.txt";
    cout<<"该文件行数为："<<CountLines(filename)<<endl;
    cout<<"\n请输入要读取的行数:"<<endl;
    while(cin>>line)
    {
        cout<<"第"<<line<<"行的内容是 ："<<endl;
        cout<<ReadLine(filename,line);
        cout<<"\n\n请输入要读取的行数:"<<endl;
    }
}

//读取文件数据到临时数组
 
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
 
 
int CountLines(char *filename)
{
    ifstream ReadFile;
    int n=0;
    string tmp;
    ReadFile.open(filename,ios::in);//ios::in 表示以只读的方式读取文件
    if(ReadFile.fail())//文件打开失败:返回0
    {
        return 0;
    }
    else//文件存在
    {
        while(getline(ReadFile,tmp,'\n'))
        {
            n++;
        }
        ReadFile.close();
        return n;
    }
}
int main()
{
    ifstream file;
    int LINES;
    char filename[512]="inFile.txt";
    file.open(filename,ios::in);
    if(file.fail())
    {
        cout<<"文件不存在."<<endl;
        file.close();
    }
    else//文件存在
    {
        LINES=CountLines(filename);
        int *tempInt=new int[LINES];
        char *tempChar=new char[LINES];
        int i=0;
        while(!file.eof()) //读取数据到数组
        {
 
            file>>tempInt[i];
            file>>tempChar[i];
            i++;
        }
        file.close(); //关闭文件
        for(i=0;i<LINES;i++)//输出数组内容
            cout<<tempInt[i]<<"\t"<<tempChar[i]<<endl;
        delete []tempInt;
        delete []tempChar;
    }
}

seekg ( pos_type position );
seekp ( pos_type position );

seekg ( off_type offset, seekdir direction );
seekp ( off_type offset, seekdir direction );

例子：
file.seekg(0,ios::beg); //让文件指针定位到文件开头
file.seekg(0,ios::end); //让文件指针定位到文件末尾
file.seekg(10,ios::cur); //让文件指针从当前位置向文件末方向移动10个字节
file.seekg(-10,ios::cur); //让文件指针从当前位置向文件开始方向移动10个字节
file.seekg(10,ios::beg); //让文件指针定位到离文件开头10个字节的位置

// obtaining file size  
   #include <iostream.h>  
   #include <fstream.h>  
     
   const char * filename = “test.txt”;  
     
   int main ()
    {  
       long l,m;  
       ifstream in(filename, ios::in|ios::binary);  
       l = in.tellg();  
       in.seekg (0, ios::end);  
       m = in.tellg();  
       in.close();  
       cout << ”size of ” << filename;  
       cout << ” is ” << (m-l) << “ bytes.\n”;  
       return 0;  
   }  
    
  //结果:  
  size of example.txt is 40 bytes.  

write ( char * buffer, streamsize size );
read ( char * buffer, streamsize size );

// reading binary file  
    #include <iostream>  
    #include <fstream.h>  
      
    const char * filename = “test.txt”;  
      
    int main () {  
        char * buffer;  
        long size;  
        ifstream in (filename, ios::in|ios::binary|ios::ate);  
        size = in.tellg();  
        in.seekg (0, ios::beg);  
        buffer = new char [size];  
        in.read (buffer, size);  
        in.close();  
          
        cout << ”the complete file is in a buffer”;  
          
        delete[] buffer;  
        return 0;  
    }  
    //运行结果：  
    The complete file is in a buffer