{"id":353,"date":"2014-08-01T07:00:00","date_gmt":"2014-08-01T07:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2014\/08\/01\/before-claiming-that-a-function-doesnt-work-you-should-check-what-youre-passing-to-it-and-what-it-returns\/"},"modified":"2014-08-01T07:00:00","modified_gmt":"2014-08-01T07:00:00","slug":"before-claiming-that-a-function-doesnt-work-you-should-check-what-youre-passing-to-it-and-what-it-returns","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20140801-00\/?p=353","title":{"rendered":"Before claiming that a function doesn't work, you should check what you're passing to it and what it returns"},"content":{"rendered":"

\nBefore claiming that a function doesn’t work,\nyou should check what you’re passing to it and what it returns,\nbecause it may be that the function is behaving just fine\nand the problem is elsewhere.\n<\/p>\n

\n

\nThe Get­Current­DirectoryW<\/code> function does\nnot appear to support directories with Unicode characters in their\nnames.\n<\/p>\n

\nwchar_t currentDirectory[MAX_PATH];\nGetCurrentDirectoryW(MAX_PATH, currentDirectory);\nwcout << currentDirectory << endl;\n<\/pre>\n
\nThe correct directory name is obtained if it contains only ASCII\ncharacters in its name,\nbut it truncates the string at the first non-ASCII character.\n<\/p>\n<\/blockquote>\n
\nIf you step through the code in the debugger,\nyou’ll see that the\nGet­Current­DirectoryW<\/code> function is\nworking just fine.\nThe buffer is filled with the current directory,\nincluding the non-ASCII characters.\nThe problem is that the wcout<\/code> stream stops printing\nthe directory name at the first\nnon-ASCII characters.\nAnd that’s because the default locale for wcout<\/cODE>\nis the \"C\"<\/code> locale, and the\n\"C\"<\/code> locale is\n\"the minimal environment for C translation.\"\nThe \"C\"<\/code> locale is\nuseless for actual work involving, you know, locales.\nYou will have to do some language-specific munging to get\nthe characters to reach the screen in the format you want,\nthe details of which are not the point of today's topic.\n<\/p>\n
\nIn other words, the bug was not in the\nGet­Current­DirectoryW<\/code> function.\nIt was in what you did with the result of the\nGet­Current­DirectoryW<\/code> function.\n<\/p>\n
\nHere's another example of thinking the problem is in a\nfunction when it isn't:\n<\/p>\n
\n
\nThe Set­Window­TextW<\/code> function does not appear\nto support Unicode, despite its name.\n<\/p>\n
\nwstring line;\nwifstream file(\"test\"); \/\/ this file is in Unicode\ngetline(file, line);\nSetWindowTextW(hwnd, line.c_str());\n<\/pre>\n<\/blockquote>\n
\nIf you look at the line<\/code> variable before you\neven get around to calling\nSet­Window­TextW<\/code>,\nyou'll see that it does not contain the text from your Unicode file.\nThe problem is that the default wifstream<\/code> reads\nthe text as an 8-bit file, and then internally converts it\n(according to the lame \"C\"<\/code> locale) to Unicode.\nIf the original file is already Unicode, you're doing a double\nconversion and things don't go well.\nYou then pass this incorrectly-converted string to\nSet­Window­TextW<\/code>,\nwhich naturally displays something different from what you intended.\n<\/p>\n
\nAgain, the point is not to delve into the intricacies of\nwifstream<\/code>.\nThe point is that the problem occurred even before you called\nSet­Window­TextW<\/code>.\nThe observed behavior, then, is simple a case of\nGarbage In, Garbage Out.\n<\/p>\n
\n\nHere's another example from a few years ago<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
Before claiming that a function doesn’t work, you should check what you’re passing to it and what it returns, because it may be that the function is behaving just fine and the problem is elsewhere. The Get­Current­DirectoryW function does not appear to support directories with Unicode characters in their names. wchar_t currentDirectory[MAX_PATH]; GetCurrentDirectoryW(MAX_PATH, currentDirectory); wcout […]<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-353","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
Before claiming that a function doesn’t work, you should check what you’re passing to it and what it returns, because it may be that the function is behaving just fine and the problem is elsewhere. The Get­Current­DirectoryW function does not appear to support directories with Unicode characters in their names. wchar_t currentDirectory[MAX_PATH]; GetCurrentDirectoryW(MAX_PATH, currentDirectory); wcout […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/353","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=353"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/353\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=353"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=353"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=353"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}