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:

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1. 1. 
      
2. #include<iostream>
3. #include<stdlib.h>
4. #include<string>
5. #include<stdio.h>
6. #include<fstream>
7. #include<dirent.h>
8. using namespace std;
9. 
   
10. void parsefile(istream& fi, ostream& fo){
11. string tmp;
12. while(fi>>tmp){
13. fo<<tmp<<endl;
14. }
15. }
16. 
    
17. void process(){
18. std::filebuf fbOut,fbIn;
19. fbOut.open("out.txt",std::ios::out);
20. std::ostream fw(&fbOut);
21. 
    
22. // Basic function testing
23. fbIn.open("test.cpp",ios::in);
24. istream is(&fbIn);
25. parsefile(is,fw);
26. 
    
27. // get all files in this directory and print it to "out.txt" iteratively
28. DIR* dir;
29. struct dirent* ent;
30. if((dir = opendir("deseq"))!=NULL){
31. while((ent = readdir(dir))!=NULL){
32. char* filename = ent->d_name;
33. if (fbIn.open(filename,ios::in)){
34. istream is(&fbIn);
35. parsefile(is,fw);//read from is and write in fw
36. fbIn.close();
37. }
38. }
39. }
40. }
41. 
    
42. int main(){
43. process();
44. return 0;
45. }
    1. 
       

其中，parsefile的声明为：void parsefile(istream& fi, ostream& fo)

注意这里函数声明必须要加引用，不然会报错：

错误：

$ g++ -g test.cpp -o b.out

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 test.cpp:1:

/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_istream<char, std::char_traits<char> >::basic_istream(const std::basic_istream<char, std::char_traits<char> >&)':

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/iosfwd:53: 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 

test.cpp: In function 'void process()':

test.cpp:24: note: synthesized method 'std::basic_istream<char, std::char_traits<char> >::basic_istream(const std::basic_istream<char, std::char_traits<char> >&)' first required here 

test.cpp:24: error: initializing argument 1 of 'void parsefile(std::istream, 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