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:

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

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

from: http://blog.csdn.net/abcjennifer/article/details/41545655