C++文件I/O示例

王朝c/c++·作者佚名  2006-01-09
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文章标题:C

原 作 者:querw

原 出 处:www.vczx.com

发 布 者:querw

发布类型:原创

发布日期:2004-10-05

今日浏览:8

总 浏 览:144

// 国庆没事写着玩的,英文很烂,请把注意力集中在代码上,呵呵:)

// c++基于流的文件操作使很多C转过来的程序员在操作文件时还是选择了 FILE*

// :)其实,C++的流操作文件也很方便啊

// 下面这个例子就是文件使用实例代码

#pragma warning(disable:4786)

#include <IOSTREAM>

#include <FSTREAM>

#include <string>

using namespace std;

int main()

{

// using std::cout;

// using std::endl;

cout<<" ********************* C ++ file opration demo ***********************"<<endl;

cout<<"using fstream or ifstream and ofstream"<<endl;

cout<<"fstream derive from istream and ostream, so most of method were defined in"<<endl;

cout<<"istream and ostream"<<endl;

cout<<"By the way, I like C style \"FILE *\" indeed. :)"<<endl;

// Input file demo

cout<<endl;

cout<<"****Part 1: Input file demo****"<<endl;

fstream /*ifstream*/ infile;

// antoher way to declare special class or function in a namespace

using std::string;

string strfilename;

cout<<"Input In FileName:"<<endl;

cin>>strfilename;

infile.open(strfilename.c_str(),ios::in/*openmode*/);

// succeed?

if(!infile)

{

cout<<"Cannot open file:"<<strfilename<<endl;

return 1;

}

// read a byte

char ch1,ch2;

infile.get(ch1);

ch2 = infile.get();

// read a line

// get(char *,int max_size,char dimiliter) can do the same word as getline()

// but get() doesn't drop the dimiliter,

// use ignore() to drop the dimiliter(the last byte,'\n' by default)

char pszLine[1024];

memset(pszLine,0,1024);

infile.getline(pszLine,1024/*read count*/,'\n'/*read until reach '\n'*/);

// seek function

// seekg means seek for getting use for input file

infile.seekg(0/*offsize*/,ios_base::beg/*seek from ios_base::beg ios_base::cur ios_base::end*/);

// read to a buffer

infile.read(pszLine,1024);

// get readed size

int nReadedSize = infile.gcount();

// tell the position also tellg() and tellp()

// tellg() before read() and tellg() after read() then you can get the readed size

// return -1 if eof() turn true

int nCurPos = infile.tellg();

// test end ?

if(infile.eof())

{

cout<<"input file reach file end"<<endl;

}

infile.close();

// output file demo

cout<<"****Part 2: Output file demo *****"<<endl;

fstream /*ofstream */outfile;

outfile.open("out.txt",ios::out);

if(!outfile)

{

cout<<"Cannot open out file out.txt."<<endl;

return 1;

}

// write a byte

char chout = 'a';

outfile.put(chout);

// write buffer

outfile.write(pszLine,strlen(pszLine));

// like ifstream ,seekp(),tellp()

outfile.seekp(10,ios_base::beg);

char buffer[] = "seekp and write a buffer";

outfile.write(buffer,strlen(buffer));

nCurPos = outfile.tellp();

outfile.close();

return 0;

}

 
 
 
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