文件读写
下面是一些文件读写的例子:
#include <fstream>
std::ifstream fin;
fin.open("文件名");
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
如果想直接读文件改一下
istream_iterator <int> in_iter(cin), in_eof;
改为
ifstream fin("rdint.txt");
istream_iterator <int> in_iter(fin), in_eof;
当然,文件开头需要:
#include <fstream>
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
//输出空行
void OutPutAnEmptyLine()
{
cout<<"\n";
}
//读取方式: 逐词读取, 词之间用空格区分
//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;
}
}
//读取方式: 逐行读取, 将行读入字符数组, 行之间用回车换行区分
//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;
}
}
//读取方式: 逐行读取, 将行读入字符串, 行之间用回车换行区分
//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;
}
}
//带错误检测的读取方式
//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(); //逐词读入字符串
OutPutAnEmptyLine(); //输出空行
ReadDataFromFileLBLIntoCharArray(); //逐词读入字符数组
OutPutAnEmptyLine(); //输出空行
ReadDataFromFileLBLIntoString(); //逐词读入字符串
OutPutAnEmptyLine(); //输出空行
ReadDataWithErrChecking(); //带检测的读取
return 0;
}