c++对文件操作的支持(一)

#include <stdio.h>
#include <iostream>
#include <fstream>
using namespace std;
void main()
{       int a,b;
char c;
ofstream fout("test.txt");
fout<<" "<<0<<" "<<1<<" "<<4<<endl;
fout<<" "<<3<<" "<<4<<" "<<'d'<<endl;
ifstream fin("test.txt");
while (!fin.eof())
{
    fin>>a>>b>>c;
    cout<<a<<" "<<b<<" "<<c<<endl;
}
cin>>a;
}

#include <iostream> 
#include <fstream> 
#include <string> 
#include <assert.h>
#include <sstream>
using namespace std;
/**
 * double转换为string
 */
string doubleToString(double d) {
 ostringstream os;
 if (os << d)
  return os.str();
 return "invalid conversion";
}
/**
 * string转double
 */
double stringToDouble(string str) {
 istringstream iss(str);
 double x;
 if (iss >> x)
  return x;
 return 0.0;
}

int main() 
{ 
    ofstream o_file;
    ifstream i_file;
    string out_text; 
    o_file.open("xie.txt"); 
    i_file.open("xie1.txt"); 
    assert(i_file.is_open()&&o_file.is_open()) ;
    while(!i_file.eof())  //while(i_file>>out_text)   也可判断结束
    {
        //将其输出到字符串中的作用是为了解决将0.000001类型输出时为科学计数法的问题
        i_file>>out_text;     //必须使用空格隔开
        static int i = 0;            //其作用为在文件结尾不会出现空的一行
        if(i ==0) o_file<<out_text;
        else    o_file<<endl<< out_text;
        i = 1;
        cout<<stringToDouble(out_text)<<endl;
        cout<<doubleToString(stringToDouble(out_text))<<endl;
    }
    i_file.close();
    o_file.close(); 
    return 0; 
}

//xie1.txt
0.000001
0.000012
0.01
0.000001