fork(1) download
copy 
  1. #include <iostream>
  2. 	#include <sstream>
  3.  
  4. 	namespace std
  5. 	{
  6. 		struct substreambuf : public streambuf
  7. 		{
  8. 			explicit substreambuf(streambuf* sbuf, streampos pos, streampos len) :
  9. 			m_sbuf(sbuf),
  10. 			m_pos(pos),
  11. 			m_len(len),
  12. 			m_read(0)
  13. 			{
  14. 				m_sbuf->pubseekpos(pos);
  15.  
  16. 				setbuf(nullptr, 0);
  17. 			}
  18.  
  19. 		protected:
  20. 			int underflow()
  21. 			{
  22. 				if (m_read >= m_len)
  23. 				{
  24. 					return traits_type::eof();
  25. 				}
  26.  
  27. 				return m_sbuf->sgetc();
  28. 			}
  29.  
  30. 			int uflow()
  31. 			{
  32. 				if (m_read >= m_len)
  33. 				{
  34. 					return traits_type::eof();
  35. 				}
  36.  
  37. 				m_read += 1;
  38.  
  39. 				return m_sbuf->sbumpc();
  40. 			}
  41.  
  42. 			streampos seekoff(streamoff off, ios_base::seekdir seekdir, ios_base::openmode openmode = ios_base::in | ios_base::out)
  43. 			{
  44. 				if (seekdir == ios_base::beg)
  45. 				{
  46. 					off += m_pos;
  47. 				}
  48. 				else if (seekdir == ios_base::cur)
  49. 				{
  50. 					off += m_pos + m_read;
  51. 				}
  52. 				else if (seekdir == ios_base::end)
  53. 				{
  54. 					off += m_pos + m_len;
  55. 				}
  56.  
  57. 				return m_sbuf->pubseekpos(off, openmode) - m_pos;
  58. 			}
  59.  
  60. 			streampos seekpos(streampos streampos, ios_base::openmode openmode = ios_base::in | ios_base::out)
  61. 			{
  62. 				streampos += m_pos;
  63.  
  64. 				if (streampos > m_pos + m_len)
  65. 				{
  66. 					return -1;
  67. 				}
  68.  
  69. 				return m_sbuf->pubseekpos(streampos, openmode) - m_pos;
  70. 			}
  71.  
  72. 		private:
  73. 			streambuf* m_sbuf;
  74. 			streampos m_pos;
  75. 			streamsize m_len;
  76. 			streampos m_read;
  77. 		};
  78. 	};
  79.  
  80. #include <iostream>
  81. 	#include <sstream>
  82.  
  83. 	using namespace std;
  84.  
  85. 	int main()
  86. 	{
  87. 		stringstream ss;
  88.  
  89. 		ss << "Hello, World!";
  90.  
  91. 		substreambuf asd(ss.rdbuf(), 0, 5);
  92.  
  93. 		istream istream(&asd);
  94.  
  95. 		char buffer[6] = { '\0' };
  96. 		istream.read(buffer, sizeof(buffer));
  97.  
  98. 		cout << buffer << endl;
  99. 	}
Success #stdin #stdout 0s 3476KB
comments ()
stdin
copy 
Standard input is empty
stdout
copy 
Hello
https://ideone.com/uGKwpy
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!