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  1. //【初心者歓迎】C/C++室 Ver.80【環境依存OK】
  2. //http://t...content-available-to-author-only...h.net/test/read.cgi/tech/1348161305/458
  3. //
  4. //458 名前：デフォルトの名無しさん[sage] 投稿日：2012/10/26(金) 18:46:38.87
  5. //ofstreamまたはifstreamでファイルが開けなかった時にcloseする必要ってありますか？
  6. //
  7. //// 例
  8. //ofstream ofs("test.txt");
  9. //if (ofs.fail()) {
  10. //　　ofs.close(); // ←これ
  11. //}
  12.  
  13. //Example for VS2010C++
  14. #include <fstream>
  15. #include <ios>
  16. #include <iostream>
  17.  
  18. #include <Shlwapi.h>
  19. #pragma comment(lib, "Shlwapi.lib")
  20.  
  21. void FileExist(const char fname[])
  22. {
  23.     bool fileexists;
  24.  
  25. 	fileexists = (::PathFileExistsA(fname) == TRUE ? true : false);
  26. 	std::cout << fname << " " << (fileexists ? "" : "does not ") << "exist" << (fileexists ? "s" : "") << "." << std::endl;
  27.  
  28. 	return;
  29. }
  30.  
  31. void ShowStates(std::ifstream *ifs)
  32. {
  33. 	std::cout << "\tifs.is_open() is " << ifs->is_open() << "." << std::endl;
  34. 	std::cout << "\tstate of bits: " << ((ifs->rdstate() & std::ios_base::eofbit) == std::ios_base::eofbit ? "eof" : "   ");
  35. 	std::cout << " " << ((ifs->rdstate() & std::ios_base::failbit) == std::ios_base::failbit ? "fail" : "    ");
  36. 	std::cout << " " << ((ifs->rdstate() & std::ios_base::badbit) == std::ios_base::badbit ? "bad" : "   ");
  37. 	std::cout << " " << (ifs->rdstate() == std::ios_base::goodbit ? "good" : "") << std::endl;
  38. 	std::cout << "\tifs.fail() is " << ifs->fail() << "." << std::endl;
  39.  
  40. 	return;
  41. }
  42.  
  43. int main(void)
  44. {
  45. 	const char ifname1[] = "main.cpp";
  46. 	const char ifname2[] = "xxx";
  47. 	const char ifname3[] = "yyy";
  48.  
  49. 	FileExist(ifname1);
  50. 	FileExist(ifname2);
  51. 	FileExist(ifname3);
  52. 	std::cout << std::endl;
  53.  
  54. 	std::cout << std::boolalpha;
  55. 	std::cout << "Example 1:" << std::endl;
  56. 	{
  57. 		std::ifstream ifs(ifname1);
  58. 		std::cout << "Create std::ifstream ifs with \"" << ifname1 << "\"." << std::endl;
  59. 		ShowStates(&ifs);
  60. 		ifs.open(ifname2);
  61. 		std::cout << "ifs.open(" << ifname2 << ") is " << ((ifs.rdstate() & std::ios_base::failbit) == std::ios_base::failbit ? "Fail" : "Success") << "." << std::endl;
  62. 		ShowStates(&ifs);
  63. 		ifs.clear();
  64. 		std::cout << "Clear state of bits." << std::endl;
  65. 		ShowStates(&ifs);
  66. 		ifs.close();
  67. 		std::cout << "ifs.close() is " << ((ifs.rdstate() & std::ios_base::failbit) == std::ios_base::failbit ? "Fail" : "Success") << "." << std::endl;
  68. 		ShowStates(&ifs);
  69. 	}
  70. 	std::cout << std::endl;
  71. 	std::cout << "Example 2:" << std::endl;
  72. 	{
  73. 		std::ifstream ifs(ifname1);
  74. 		std::cout << "Create std::ifstream ifs with \"" << ifname1 << "\"." << std::endl;
  75. 		ShowStates(&ifs);
  76. 		std::cout << "ifs.rdbuf()->open(" << ifname2 << ") is " << (ifs.rdbuf()->open(ifname2, std::ios_base::in) == NULL ? "False" : "Success") << "." << std::endl;
  77. 		ShowStates(&ifs);
  78. 		std::cout << "ifs.rdbuf()->close() is " << (ifs.rdbuf()->close() == NULL ? "Fail" : "Success") << "." << std::endl;
  79. 		ShowStates(&ifs);
  80. 	}
  81. 	std::cout << std::endl;
  82. 	std::cout << "Example 3:" << std::endl;
  83. 	{
  84. 		std::ifstream ifs(ifname1);
  85. 		std::cout << "Create std::ifstream ifs with \"" << ifname1 << "\"." << std::endl;
  86. 		ShowStates(&ifs);
  87. 		ifs.close();
  88. 		std::cout << "ifs.close() is " << ((ifs.rdstate() & std::ios_base::failbit) == std::ios_base::failbit ? "Fail" : "Success") << "." << std::endl;
  89. 		ShowStates(&ifs);
  90. 		ifs.open(ifname2);
  91. 		std::cout << "ifs.open(" << ifname2 << ") is " << ((ifs.rdstate() & std::ios_base::failbit) == std::ios_base::failbit ? "Fail" : "Success") << "." << std::endl;
  92. 		ShowStates(&ifs);
  93. 		ifs.close();
  94. 		std::cout << "ifs.close() is " << ((ifs.rdstate() & std::ios_base::failbit) == std::ios_base::failbit ? "Fail" : "Success") << "." << std::endl;
  95. 		ShowStates(&ifs);
  96. 	}
  97. 	std::cout << std::endl;
  98. 	std::cout << "Example 4:" << std::endl;
  99. 	{
  100. 		std::ifstream ifs(ifname1);
  101. 		std::cout << "Create std::ifstream ifs with \"" << ifname1 << "\"." << std::endl;
  102. 		ShowStates(&ifs);
  103. 		std::cout << "ifs.rdbuf()->close() is " << (ifs.rdbuf()->close() == NULL ? "Fail" : "Success") << "." << std::endl;
  104. 		ShowStates(&ifs);
  105. 		std::cout << "ifs.rdbuf()->open(" << ifname2 << ") is " << (ifs.rdbuf()->open(ifname2, std::ios_base::in) == NULL ? "False" : "Success") << "." << std::endl;
  106. 		ShowStates(&ifs);
  107. 		std::cout << "ifs.rdbuf()->close() is " << (ifs.rdbuf()->close() == NULL ? "Fail" : "Success") << "." << std::endl;
  108. 		ShowStates(&ifs);
  109. 	}
  110. 	std::cout << std::endl;
  111. 	std::cout << "Example 5:" << std::endl;
  112. 	{
  113. 		std::ifstream ifs(ifname3);
  114. 		std::cout << "Create std::ifstream ifs with \"" << ifname3 << "\"." << std::endl;
  115. 		ShowStates(&ifs);
  116. 		ifs.clear();
  117. 		std::cout << "Clear state of bits." << std::endl;
  118. 		ShowStates(&ifs);
  119. 		ifs.close();
  120. 		std::cout << "ifs.close() is " << ((ifs.rdstate() & std::ios_base::failbit) == std::ios_base::failbit ? "Fail" : "Success") << "." << std::endl;
  121. 		ShowStates(&ifs);
  122. 	}
  123. 	std::cout << std::endl;
  124. 	std::cout << "Example 6:" << std::endl;
  125. 	{
  126. 		std::ifstream ifs(ifname3);
  127. 		std::cout << "Create std::ifstream ifs with \"" << ifname3 << "\"." << std::endl;
  128. 		ShowStates(&ifs);
  129. 		std::cout << "ifs.rdbuf()->close() is " << (ifs.rdbuf()->close() == NULL ? "Fail" : "Success") << "." << std::endl;
  130. 		ShowStates(&ifs);
  131. 	}
  132. 	return 0;
  133. }
  134.  
  135. //OUTPUT
  136. //==========
  137.  
  138. //main.cpp exists.
  139. //xxx exists.
  140. //yyy does not exist.
  141. //
  142. //Example 1:
  143. //Create std::ifstream ifs with "main.cpp".
  144. //        ifs.is_open() is true.
  145. //        state of bits:              good
  146. //        ifs.fail() is false.
  147. //ifs.open(xxx) is Fail.
  148. //        ifs.is_open() is true.
  149. //        state of bits:     fail
  150. //        ifs.fail() is true.
  151. //Clear state of bits.
  152. //        ifs.is_open() is true.
  153. //        state of bits:              good
  154. //        ifs.fail() is false.
  155. //ifs.close() is Success.
  156. //        ifs.is_open() is false.
  157. //        state of bits:              good
  158. //        ifs.fail() is false.
  159. //
  160. //Example 2:
  161. //Create std::ifstream ifs with "main.cpp".
  162. //        ifs.is_open() is true.
  163. //        state of bits:              good
  164. //        ifs.fail() is false.
  165. //ifs.rdbuf()->open(xxx) is False.
  166. //        ifs.is_open() is true.
  167. //        state of bits:              good
  168. //        ifs.fail() is false.
  169. //ifs.rdbuf()->close() is Success.
  170. //        ifs.is_open() is false.
  171. //        state of bits:              good
  172. //        ifs.fail() is false.
  173. //
  174. //Example 3:
  175. //Create std::ifstream ifs with "main.cpp".
  176. //        ifs.is_open() is true.
  177. //        state of bits:              good
  178. //        ifs.fail() is false.
  179. //ifs.close() is Success.
  180. //        ifs.is_open() is false.
  181. //        state of bits:              good
  182. //        ifs.fail() is false.
  183. //ifs.open(xxx) is Success.
  184. //        ifs.is_open() is true.
  185. //        state of bits:              good
  186. //        ifs.fail() is false.
  187. //ifs.close() is Success.
  188. //        ifs.is_open() is false.
  189. //        state of bits:              good
  190. //        ifs.fail() is false.
  191. //
  192. //Example 4:
  193. //Create std::ifstream ifs with "main.cpp".
  194. //        ifs.is_open() is true.
  195. //        state of bits:              good
  196. //        ifs.fail() is false.
  197. //ifs.rdbuf()->close() is Success.
  198. //        ifs.is_open() is false.
  199. //        state of bits:              good
  200. //        ifs.fail() is false.
  201. //ifs.rdbuf()->open(xxx) is Success.
  202. //        ifs.is_open() is true.
  203. //        state of bits:              good
  204. //        ifs.fail() is false.
  205. //ifs.rdbuf()->close() is Success.
  206. //        ifs.is_open() is false.
  207. //        state of bits:              good
  208. //        ifs.fail() is false.
  209. //
  210. //Example 5:
  211. //Create std::ifstream ifs with "yyy".
  212. //        ifs.is_open() is false.
  213. //        state of bits:     fail
  214. //        ifs.fail() is true.
  215. //Clear state of bits.
  216. //        ifs.is_open() is false.
  217. //        state of bits:              good
  218. //        ifs.fail() is false.
  219. //ifs.close() is Fail.
  220. //        ifs.is_open() is false.
  221. //        state of bits:     fail
  222. //        ifs.fail() is true.
  223. //
  224. //Example 6:
  225. //Create std::ifstream ifs with "yyy".
  226. //        ifs.is_open() is false.
  227. //        state of bits:     fail
  228. //        ifs.fail() is true.
  229. //ifs.rdbuf()->close() is Fail.
  230. //        ifs.is_open() is false.
  231. //        state of bits:     fail
  232. //        ifs.fail() is true.
  233.  
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https://ideone.com/ouBVuh
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
secret

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