{"id":92,"date":"2018-12-26T02:35:59","date_gmt":"2018-12-26T05:35:59","guid":{"rendered":"http:\/\/35.243.195.209\/?p=92"},"modified":"2018-12-26T02:35:59","modified_gmt":"2018-12-26T05:35:59","slug":"string-in-c","status":"publish","type":"post","link":"https:\/\/nanzhou.cc\/index.php\/2018\/12\/26\/string-in-c\/","title":{"rendered":"String in C++"},"content":{"rendered":"

Summary<\/h2>\n

In this post, I will introduce the string<\/code> class in c++ STL. It covers useful APIs and some of my recommendations.
\n1. Split<\/a>
\n2. Access<\/a>
\n3. Comparison<\/a>
\n4. Numeric-Conversions<\/a><\/p>\n

Details<\/h2>\n

<\/a><\/p>\n

Split<\/h3>\n

Thanks to this post<\/a>, we present the conlusions for split<\/code> first.
\n1. If you have access to boost<\/a>, please do Solution 1.
\n2. You do not want to include other libraries. Implement own algorithms using Solution 2.
\n3. Use stream and see Solution 3.<\/p>\n

Solutions<\/h4>\n
1. boost<\/h5>\n
#include <boost\/algorithm\/string.hpp>\n\nstd::string text = \"Let me split this into words\";\nstd::vector<std::string> results;\n\nboost::split(results, text, [](char c){return c == ' ';});\n<\/code><\/pre>\n
Boost::split essentially performs multiple find_if on the string on the delimiter, until reaching the end.<\/p>\n
It allows even several different delimiters<\/code> and is 60% faster than solution 3.<\/p>\n
2. getline<\/h5>\n
char delimiter = ',';\nstd::vector<std::string> tokens;\nstd::string token;\nstd::istringstream tokenStream(s);\nwhile (std::getline(tokenStream, token, delimiter))\n{\n    tokens.push_back(token);\n}\n<\/code><\/pre>\n
3. stream<\/h5>\n
std::string text = \"Let me split this into words\";\n\nstd::istringstream iss(text);\nstd::vector<std::string> results(std::istream_iterator<std::string>{iss},\n                                 std::istream_iterator<std::string>()); \/\/ only works for space\n<\/code><\/pre>\n
<\/a><\/p>\n
Access<\/h3>\n
Actually string<\/code> acts like vector<char><\/code>, we recommend you use .at()<\/code> rather than []<\/code>, since .at()<\/code> check the boundary and throw exceptions.<\/p>\n
string str = \"hello\";\ncout << str.at(100) << endl; \/\/ libc++abi.dylib: terminating with uncaught exception of type std::out_of_range: basic_string\ncout << str[100] << endl; \/\/ exit normally, print something you do not really know\n<\/code><\/pre>\n
<\/a><\/p>\n
Comparison<\/h3>\n
We can use !=<\/code> and ==<\/code> directly.<\/p>\n
For <<\/code> and ><\/code>, <\/p>\n\n\n\n\n\n\n
value<\/th>\nrelation between compared string<\/em> and comparing string<\/em><\/th>\n<\/tr>\n<\/thead>\n
< 0<\/td>\nEither the value of the first character that does not match is lower in the compared string<\/em>, or all compared characters match but the compared string<\/em> is shorter.<\/td>\n<\/tr>\n
> 0<\/td>\nEither the value of the first character that does not match is greater in the compared string<\/em>, or all compared characters match but the compared string<\/em> is longer.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\"abc\" < \"abcd\"; \/\/ true\n\"abc\" < \"bbc\" ; \/\/ true\n<\/code><\/pre>\n
<\/a><\/p>\n
Numeric Conversions<\/h3>\n
The functions throw a std::invalid_argument exception if the conversion is not possible and a std::out_of_range exception if the determined value is too big for the destination.<\/p>\n
#include <cfloat>\ncout << INT_MAX << endl;\ncout << DBL_MAX << endl;\ncout << FLT_MAX << endl;\n\/*\n2147483647\n1.79769e+308\n3.40282e+38\n*\/\n<\/code><\/pre>\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Method<\/strong><\/th>\nDescription<\/strong><\/th>\n<\/tr>\n<\/thead>\n
std::to_string(val)<\/code><\/td>\nConverts val<\/code> into a std::string<\/code>.<\/td>\n<\/tr>\n
std::stoi(str)<\/code><\/td>\nReturns an int<\/code> value.<\/td>\n<\/tr>\n
std::stol(str)<\/code><\/td>\nReturns a long<\/code> value.<\/td>\n<\/tr>\n
std::stoll(str)<\/code><\/td>\nReturns a long long<\/code> value.<\/td>\n<\/tr>\n
std::stoul(str)<\/code><\/td>\nReturns an unsigned long<\/code> value.<\/td>\n<\/tr>\n
std::stoull(str)<\/code><\/td>\nReturns an unsigned long long<\/code> value.<\/td>\n<\/tr>\n
std::stof(str)<\/code><\/td>\nReturns a float<\/code> value.<\/td>\n<\/tr>\n
std::stod(str)<\/code><\/td>\nReturns a double<\/code> value.<\/td>\n<\/tr>\n
std::stold(str)<\/code><\/td>\nReturns an long double<\/code> value.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"excerpt":{"rendered":"
Summary In this post, I will introduce the string class in c++ STL. It covers useful APIs and some of my recommendations. 1. Split 2. Access 3. Comparison 4. Numeric-Conversions Details Split Thanks to this post, we present the conlusions for split first. 1. If you have access to boost, please do Solution 1. 2….<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,5],"tags":[],"class_list":["post-92","post","type-post","status-publish","format-standard","hentry","category-c","category-proglang"],"_links":{"self":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/92","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/comments?post=92"}],"version-history":[{"count":10,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/92\/revisions"}],"predecessor-version":[{"id":135,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/92\/revisions\/135"}],"wp:attachment":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/media?parent=92"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/categories?post=92"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/tags?post=92"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}