{"id":55,"date":"2007-07-02T03:17:48","date_gmt":"2007-07-02T08:17:48","guid":{"rendered":"http:\/\/mariusbancila.ro\/blog\/?p=55"},"modified":"2007-07-02T03:23:57","modified_gmt":"2007-07-02T08:23:57","slug":"case-insensitive-strings","status":"publish","type":"post","link":"https:\/\/mariusbancila.ro\/blog\/2007\/07\/02\/case-insensitive-strings\/","title":{"rendered":"Case Insensitive Strings"},"content":{"rendered":"

Recently I’ve been asked how you can make method find of std::string case insensitive. An obvious solution is to transform the strings to lower case, for instance,?and perform the search in lower case. The solution has some inconvenients and a clean and nice solution is defining custom traits that ignore the case. The solution I’m showing bellow is based on\u00a0an example from the book “The C++ Standard Library – A Tutorial and Reference” by Nicolai M. Josuttis (Addison Wesley, 1999). The original example is available online on the author’s web page: http:\/\/www.josuttis.com\/libbook\/string\/icstring1.cpp.html<\/a>.<\/p>\n

What I’m showing below is a modified implementation that allows working both with strings of char and wchar_t.<\/p>\n

For the start, a custom char_traits implementation must be provided:<\/p>\n

\r\n\/\/ define a custom traits class that ignores case\r\ntemplate<typename T> struct ignorecase_traits : public std::char_traits<T>\r\n{\r\n\ttypedef T\t\tchar_type;\r\n\ttypedef int\t\tint_type;\r\n\ttypedef std::streamoff\toff_type;\r\n\ttypedef std::streampos\tpos_type;\r\n\ttypedef std::mbstate_t\tstate_type;\r\n\r\n\t\/\/ Performs the assignment dst = src\r\n\tstatic void assign(char_type& dst, const char_type src)\r\n\t{\r\n\t\tdst = src;\r\n\t}\r\n\r\n\t\/\/ Assigns the value c to each pointer in the range [dst, dst+n), and returns dst \r\n\tstatic char_type* assign(char_type* dst, size_t n, char_type c)\r\n\t{\r\n\t\treturn static_cast<char_type*>(std::memset(dst, n, c));\r\n\t}\r\n\r\n\t\/\/ return whether c1 and c2 are equal\r\n\tstatic bool eq(const char_type& c1, const char_type& c2)\r\n\t{\r\n\t\treturn std::toupper(c1)==std::toupper(c2);\r\n\t}\r\n\r\n\t\/\/ return whether c1 is less than c2\r\n\tstatic bool lt(const char_type& c1, const char_type& c2)\r\n\t{\r\n\t\treturn std::toupper(c1) < std::toupper(c2);\r\n\t}\r\n\r\n\t\/\/ compare up to n characters of s1 and s2\r\n\tstatic int compare(const char_type* s1, const char_type* s2, std::size_t n)\r\n\t{\r\n\t\tfor (std::size_t i=0; i < n; ++i)\r\n\t\t{\r\n\t\t\tif (!eq(s1[i], s2[i]))\r\n\t\t\t{\r\n\t\t\t\treturn lt(s1[i], s2[i])?-1:1;\r\n\t\t\t}\r\n\t\t}\r\n\t\treturn 0;\r\n\t}\r\n\r\n\t\/\/ search c in s\r\n\tstatic const char_type* find(const char_type* s, std::size_t n, const char_type& c)\r\n\t{\r\n\t\tfor (std::size_t i=0; i < n; ++i)\r\n\t\t{\r\n\t\t\tif (eq(s[i], c))\r\n\t\t\t{\r\n\t\t\t\treturn &(s[i]);\r\n\t\t\t}\r\n\t\t}\r\n\t\treturn 0;\r\n\t}\r\n};\r\n<\/pre>\n
\nStructure ignorecase_traits is parameterized, so that we will be able to instantiate it both for char and wchar_t. Two typedefs of basic_string with the new ignorechar_traits are necessary:<\/p>\n
\r\n\/\/ define a special type for a string of char\r\ntypedef std::basic_string<char, ignorecase_traits<char>> icstring;\r\n\r\n\/\/ define a special type for a strings of wchar_t\r\ntypedef std::basic_string<wchar_t, ignorecase_traits<wchar_t>> icwstring;\r\n<\/pre>\n
\nTo be able to print objects of type icstring or icwstring an overload of operator<< is required:<\/p>\n
\r\ntemplate <typename T>\r\ninline std::basic_ostream<T>& operator << (std::basic_ostream<T>& strm,\r\n    const std::basic_string<T, ignorecase_traits<T>>& s)\r\n{\r\n\treturn strm << s.c_str();\r\n}\r\n<\/pre>\n
\nHaving all that implemented, we can use the two types, like the shown below:<\/p>\n
\r\nint _tmain(int argc, _TCHAR* argv[])\r\n{\r\n\ticstring is1(\"marius\");\r\n\ticstring is2(\"marIUS\");\r\n\r\n\tstd::cout << std::boolalpha;\r\n\tstd::cout << is1 << \" == \" << is2 << \" : \" << (is1==is2) << std::endl;\r\n\r\n\ticwstring iws1(L\"bancila\");\r\n\ticwstring iws2(L\"banCILA\");\r\n\r\n\tstd::wcout << std::boolalpha;\r\n\tstd::wcout << iws1 << L\" == \" << iws2 << L\" : \" << (iws1==iws2) << std::endl;\r\n\r\n\tif(is2.find(\"Riu\") != std::string::npos)\r\n\t\tstd::cout << \"Riu found in \" << is2 << std::endl;\r\n\r\n\tstd::wstring ws1(L\"cil\");\r\n\ticwstring iws3(ws1.begin(), ws1.end());\r\n\r\n\tif(iws2.find(iws3) != std::string::npos)\r\n\t\tstd::wcout << iws3 << L\" found in \" << iws2 << std::endl;\r\n\r\n\treturn 0;\r\n}\r\n<\/pre>\n
\nIf you run the code you’ll get the following output:<\/p>\n
\r\nmarius == marIUS : true \r\nbancila == banCILA : true \r\nRiu found in marIUS \r\ncil found in banCILA\r\n<\/pre>\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
Recently I’ve been asked how you can make method find of std::string case insensitive. An obvious solution is to transform the strings to lower case, for instance,?and perform the search in lower case. The solution has some inconvenients and a clean and nice solution is defining custom traits that ignore the case. The solution I’m … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[7],"tags":[],"class_list":["post-55","post","type-post","status-publish","format-standard","hentry","category-c"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t