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  1. #include <iostream>
  2. #include <fstream>
  3. #include <stdio.h>
  4.  
  5. namespace fs
  6. {
  7.     class tempfile
  8. 	{
  9. 	public:
  10. 		// tempfile constructor.
  11. 		explicit tempfile(char const * const _file_name, std::ios_base::openmode _mode = std::ios_base::binary, char const * const _temp_dir = 0 , char const * const _prefix = "tfx") :
  12. 			m_file_name( _file_name ),
  13. 			m_temp_name( tempnam(_temp_dir, _prefix) ),
  14. 			m_temp_file( m_temp_name.c_str(), std::ios_base::out | _mode )
  15. 		{
  16. 		}
  17.  
  18. 		// check to see if the temp file is open and ready for writing.
  19. 		bool is_open() const
  20. 		{
  21. 			return m_temp_file.is_open();
  22. 		}
  23.  
  24. 		// boolean operator returns true if the temporary file is ready for writing.
  25. 		operator bool() const
  26. 		{
  27. 			return is_open();
  28. 		}
  29.  
  30. 		// get the temporary file stream.
  31. 		std::ofstream & temp()
  32. 		{
  33. 			return m_temp_file;
  34. 		}
  35.  
  36. 		// closes the temp file but doesn't commit the changes.
  37. 		void close( bool erase_temp = false )
  38. 		{
  39. 			// close the temp file.
  40. 			if ( m_temp_file )
  41. 				m_temp_file.close();
  42.  
  43. 			// kill the temp file.
  44. 			if ( erase_temp )
  45. 				cleanup();
  46. 		}
  47.  
  48. 		// erase the temporary file.
  49. 		void cleanup()
  50. 		{
  51. 			remove( m_temp_name.c_str() );
  52. 		}
  53.  
  54. 		// replaces the final file with the temporary. note: every
  55. 		// attempt is made to preserve the original file.
  56. 		bool commit( bool keep_backup = true )
  57. 		{
  58. 			if ( is_open() ) {
  59. 				// close the temp file to move the contents.
  60. 				close( false );
  61.  
  62. 				// add backup strategies to handle backup.  three strategy ideas: 
  63. 				//      1. delete - delete the original file.
  64. 				//      2. rename - rename the original file (ie, keep backup).
  65. 				//      3. archive - store the file in source control or database or offsite.
  66. 				// for now, rename the old file.
  67. 				std::string oldfilename = m_file_name;
  68. 				oldfilename += std::string(".bck");
  69. 				remove( oldfilename.c_str() );
  70. 				rename( m_file_name.c_str(), oldfilename.c_str() );
  71.  
  72. 				// rename it to the new file.
  73. 				if ( rename(m_temp_name.c_str(), m_file_name.c_str()) == 0 )
  74. 				{
  75. 					if (!keep_backup) 
  76. 						remove( oldfilename.c_str() );
  77.  
  78. 					return true;
  79. 				}
  80.  
  81. 				// if temp rename fails, restore the original file.
  82. 				remove( m_file_name.c_str() );
  83. 				rename( oldfilename.c_str(), m_file_name.c_str() );
  84. 			}
  85.  
  86. 			// if you get here, attempt to close & remove the temporary file.
  87. 			close( true );
  88.  
  89. 			return false;
  90. 		}
  91.  
  92. 		// close the file assuming we will explicitly commit the results. 
  93. 		~tempfile()
  94. 		{
  95. 			close( true );
  96. 		}
  97.  
  98. 	private:
  99. 		std::string			m_file_name;
  100. 		std::string         m_temp_name;
  101. 		std::ofstream		m_temp_file;
  102.  
  103. 	private:
  104. 		tempfile(); // disabled
  105. 	};
  106. }
  107.  
  108. int main()
  109. {
  110.     fs::tempfile test("test.txt");
  111.  
  112. 	if ( test ) {
  113. 		test.temp() << "nothing to see here...\n";
  114.  
  115. 		if ( test.commit() )
  116. 			std::cout << "Success!" << std::endl;
  117. 		else
  118. 			std::cout << "Failure :( " << std::endl;
  119. 	}
  120.  
  121. 	return 0;
  122. }
  123.  
  124.  
  125.  
Success #stdin #stdout 0.02s 2816KB
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Failure :(
https://ideone.com/6gh1J7
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
secret

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