istream, outstream使用及常见错误

使用方法：

使用filebuf打开文件，并拷贝给istream/ostream。

如下面的例子中，实现读取并处理deseq文件夹下所有文件，输出到ostream fw.

code:

头文件：

#include<iostream>
#include<stdlib.h>
#include<string.h>
#include<stdio.h>
#include<fstream>
#include<dirent.h>

调用：

void process(char* filename){
    std::filebuf fbOut,fbIn;
    fbOut.open("kw_fea.txt",std::ios::out);
    std::ostream fw(&fbOut);

    DIR* dir;
    struct dirent* ent;
    if((dir = opendir("deseq"))!=NULL){
        while((ent = readdir(dir))!=NULL){
            char* filename = ent->d_name;
            if (fbIn.open(filename,ios::in)){
                istream is(&fbIn);
                parsefile(fw);
		fbIn.close();
            }
        }
    }
}

其中，parsefile的声明为：bool parsefile(ostream &fw)

注意这里函数声明必须要加引用，不然会报错：

错误：

In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ios:39,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:40,
                 from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iostream:40,
                 from read.cpp:10:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ios_base.h: In copy constructor ‘std::basic_ios<char, std::char_traits<char> >::basic_ios(const std::basic_ios<char, std::char_traits<char> >&)‘:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ios_base.h:790: error: ‘std::ios_base::ios_base(const std::ios_base&)‘ is private
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iosfwd:47: error: within this context
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iosfwd: In copy constructor ‘std::basic_ostream<char, std::char_traits<char> >::basic_ostream(const std::basic_ostream<char, std::char_traits<char> >&)‘:
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iosfwd:56: note: synthesized method ‘std::basic_ios<char, std::char_traits<char> >::basic_ios(const std::basic_ios<char, std::char_traits<char> >&)‘ first required here 
read.cpp: In function ‘void process(char*)‘:
read.cpp:105: note: synthesized method ‘std::basic_ostream<char, std::char_traits<char> >::basic_ostream(const std::basic_ostream<char, std::char_traits<char> >&)‘ first required here 
read.cpp:105: error:   initializing argument 1 of ‘bool parsefile(std::ostream)‘

原因是stream类型数据不支持拷贝，所以必须传址。

参考：http://stackoverflow.com/questions/6457591/problem-with-ostream-ofstream-inheritance