如何使map :: find操作不区分大小写? [英] How can I make the map::find operation case insensitive?
问题描述
map::find
方法是否支持不区分大小写的搜索?我有一张地图,如下所示:
Does the map::find
method support case insensitive search? I have a map as follows:
map<string, vector<string> > directory;
,并希望下面的搜索忽略大小写:
and want the below search to ignore case:
directory.find(search_string);
推荐答案
默认情况下不启用.您将必须提供一个自定义比较器作为第三个参数.以下代码段将帮助您...
It does not by default. You will have to provide a custom comparator as a third argument. Following snippet will help you...
/************************************************************************/
/* Comparator for case-insensitive comparison in STL assos. containers */
/************************************************************************/
struct ci_less : std::binary_function<std::string, std::string, bool>
{
// case-independent (ci) compare_less binary function
struct nocase_compare : public std::binary_function<unsigned char,unsigned char,bool>
{
bool operator() (const unsigned char& c1, const unsigned char& c2) const {
return tolower (c1) < tolower (c2);
}
};
bool operator() (const std::string & s1, const std::string & s2) const {
return std::lexicographical_compare
(s1.begin (), s1.end (), // source range
s2.begin (), s2.end (), // dest range
nocase_compare ()); // comparison
}
};
像std::map< std::string, std::vector<std::string>, ci_less > myMap;
注意:std :: lexicographical_compare包含一些细节.如果考虑语言环境,字符串比较并不总是那么简单.如果有兴趣,请参见clc ++上的此线程.
NOTE: std::lexicographical_compare has some nitty-gritty details. String comparison isn't always straightforward if you consider locales. See this thread on c.l.c++ if interested.
更新:使用C ++ 11时,不推荐使用std::binary_function
,这是不必要的,因为会自动推断类型.
UPDATE: With C++11 std::binary_function
is deprecated and is unnecessary as the types are deduced automatically.
struct ci_less
{
// case-independent (ci) compare_less binary function
struct nocase_compare
{
bool operator() (const unsigned char& c1, const unsigned char& c2) const {
return tolower (c1) < tolower (c2);
}
};
bool operator() (const std::string & s1, const std::string & s2) const {
return std::lexicographical_compare
(s1.begin (), s1.end (), // source range
s2.begin (), s2.end (), // dest range
nocase_compare ()); // comparison
}
};
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