檔案讀寫

下面是一些檔案讀寫的例子：

 

#include   <fstream>  
  std::ifstream   fin;  
  fin.open("檔案名稱");  
  while   (!fin.eof())  
  {  
  char*   pChar   =new   char[255];  
  fin.getline(pChar,255);//   每一行就到pChar中去：)  
                      ………………    
                      ………………  
   
                      }

 

 

 

 

 

#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;

int file_to_vector(const string& filename,vector <string>&svec)
{
ifstream infile(filename.c_str());
if(!infile.is_open())
    return 1;
string s;
while(getline(infile,s))
svec.push_back(s);
infile.close();
if(infile.eof())
return 4;
if(infile.bad())
return 2;
if(infile.fail())
return 3;
}

int main()
{
vector <string>svec;
string filename,s;
cout < <"Enter filename : " < <endl;
cin>>filename;
switch(file_to_vector(filename,svec))
{
case 1:cout < <"error!can not open file: " < <filename < <endl;return -1;break;

case 2:cout < <"error!systerm failure" < <endl;return -1;

case 3:cout < <"error!read failure" < <endl;return -1;
}
cout < <"Vector: " < <endl;
for(vector <string>::iterator iter=svec.begin();iter!=svec.end();++iter)
cout < <*iter < <endl;
return 0;
}

 

 

 

#include <iostream>
#include <fstream>
#include <vector>
#include <cstdlib>
using namespace std;

int main()
{
    vector <int> ch;
vector <int> ::iterator iter;
int ival;
    ifstream infile("a.txt");
    if(!infile.is_open())
{
cerr < <"Error! can not open file!" < <endl;
exit(EXIT_FAILURE);
}
else
{
        while(infile>>ival)
{
          ch.push_back(ival);
}
        for(iter=ch.begin();iter!=ch.end();++iter)
cout < <*iter < <endl;
}
    return 0;
}

 

 

 

 

 

include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>

using namespace std;

int
main(void)
{
        vector<int> v;
        istream_iterator<int> in_iter(cin), in_eof;
        ostream_iterator<int> out_iter(cout, "\n");

        for(; in_iter != in_eof; ++in_iter)
                v.push_back(*in_iter);

        copy(v.begin(), v.end(), out_iter);

        return 0;
}

$ cat rdint.txt
1 2 3 4 5
6 7 8 9 10

$ cat rdint.txt | ./rdint
1
2
3
4
5
6
7
8
9
10
如果想直接讀檔案改一下
istream_iterator <int> in_iter(cin), in_eof;
改為
ifstream fin("rdint.txt");
istream_iterator <int> in_iter(fin), in_eof;
當然，檔案開頭需要：
#include <fstream>

 

 

 

 

 

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

//輸出空行
void OutPutAnEmptyLine()
{
    cout<<"\n";
}

//讀取方式: 逐詞讀取, 詞之間用空格區分
//read data from the file, Word By Word
//when used in this manner, we'll get space-delimited bits of text from the file
//but all of the whitespace that separated words (including newlines) was lost.
void ReadDataFromFileWBW()
{
    ifstream fin("data.txt"); 
    string s; 
    while( fin >> s )
    {   
        cout << "Read from file: " << s << endl; 
    }
}

//讀取方式: 逐行讀取, 將行讀入字元數組, 行之間用斷行符號換行區分
//If we were interested in preserving whitespace,
//we could read the file in Line-By-Line using the I/O getline() function.
void ReadDataFromFileLBLIntoCharArray()
{
    ifstream fin("data.txt");
    const int LINE_LENGTH = 100;
    char str[LINE_LENGTH]; 
    while( fin.getline(str,LINE_LENGTH) )
    {   
        cout << "Read from file: " << str << endl;
    }
}

//讀取方式: 逐行讀取, 將行讀入字串, 行之間用斷行符號換行區分
//If you want to avoid reading into character arrays,
//you can use the C++ string getline() function to read lines into strings
void ReadDataFromFileLBLIntoString()
{
    ifstream fin("data.txt"); 
    string s; 
    while( getline(fin,s) )
    {   
        cout << "Read from file: " << s << endl;
    }
}

//帶錯誤偵測的讀取方式
//Simply evaluating an I/O object in a boolean context will return false
//if any errors have occurred
void ReadDataWithErrChecking()
{
    string filename = "dataFUNNY.txt"; 
    ifstream fin( filename.c_str()); 
    if( !fin )
    {  
        cout << "Error opening " << filename << " for input" << endl;  
        exit(-1); 
    }
}

int main()
{
    ReadDataFromFileWBW(); //逐詞讀入字串
    OutPutAnEmptyLine(); //輸出空行

    ReadDataFromFileLBLIntoCharArray(); //逐詞讀入字元數組
    OutPutAnEmptyLine(); //輸出空行

    ReadDataFromFileLBLIntoString(); //逐詞讀入字串
    OutPutAnEmptyLine(); //輸出空行

    ReadDataWithErrChecking(); //帶檢測的讀取
    return 0;
}