C++ 不区分大小写的std::字符串集
如何在std::set中插入或搜索不区分大小写的字符串 比如说-C++ 不区分大小写的std::字符串集,c++,stl,C++,Stl,如何在std::set中插入或搜索不区分大小写的字符串 比如说- std::set<std::string> s; s.insert("Hello"); s.insert("HELLO"); //not allowed, string already exists. std::set s; s、 插入(“你好”); s、 插入(“你好”)//不允许,字符串已存在。 std::set提供了提供您自己的比较器的可能性(大多数std容器也是如此)。然后,您可以执行任何类型的比较。完整示例
std::set<std::string> s;
s.insert("Hello");
s.insert("HELLO"); //not allowed, string already exists.
std::set s;
s、 插入(“你好”);
s、 插入(“你好”)//不允许,字符串已存在。
std::set提供了提供您自己的比较器的可能性(大多数std容器也是如此)。然后,您可以执行任何类型的比较。完整示例可用您需要定义自定义比较器:
struct InsensitiveCompare {
bool operator() (const std::string& a, const std::string& b) const {
return strcasecmp(a.c_str(), b.c_str()) < 0;
}
};
std::set<std::string, InsensitiveCompare> s;
struct InsensitiveCompare{
布尔运算符()(常数std::string&a,常数std::string&b)常数{
返回strcasecmp(a.c_str(),b.c_str())<0;
}
};
std::集s;
如果
straccmp
不可用,您可以尝试stricmp
或strcoll
。据我所知,这比stricmp()更具可移植性,因为stricmp()实际上不是std库的一部分,但仅由大多数编译器供应商实现。因此,下面是我的解决方案,只是滚动你自己的
#include <string>
#include <cctype>
#include <iostream>
#include <set>
struct caseInsensitiveLess
{
bool operator()(const std::string& x, const std::string& y)
{
unsigned int xs ( x.size() );
unsigned int ys ( y.size() );
unsigned int bound ( 0 );
if ( xs < ys )
bound = xs;
else
bound = ys;
{
unsigned int i = 0;
for (auto it1 = x.begin(), it2 = y.begin(); i < bound; ++i, ++it1, ++it2)
{
if (tolower(*it1) < tolower(*it2))
return true;
if (tolower(*it2) < tolower(*it1))
return false;
}
}
return false;
}
};
int main()
{
std::set<std::string, caseInsensitiveLess> ss1;
std::set<std::string> ss2;
ss1.insert("This is the first string");
ss1.insert("THIS IS THE FIRST STRING");
ss1.insert("THIS IS THE SECOND STRING");
ss1.insert("This IS THE SECOND STRING");
ss1.insert("This IS THE Third");
ss2.insert("this is the first string");
ss2.insert("this is the first string");
ss2.insert("this is the second string");
ss2.insert("this is the second string");
ss2.insert("this is the third");
for ( auto& i: ss1 )
std::cout << i << std::endl;
std::cout << std::endl;
for ( auto& i: ss2 )
std::cout << i << std::endl;
}
这是一个通用的解决方案,也适用于除
std::string
以外的其他字符串类型(使用std::wstring
,std::string\u视图
,char const*
进行测试)。基本上,任何定义一组字符的东西都应该起作用
这里的关键点是使用它,它允许我们在比较器中统一处理以null结尾的字符数组、字符指针和范围
通用代码(“iset.h”):
#pragma once
#include <set>
#include <algorithm>
#include <boost/algorithm/string.hpp>
#include <boost/range/as_literal.hpp>
// Case-insensitive generic string comparator.
struct range_iless
{
template< typename InputRange1, typename InputRange2 >
bool operator()( InputRange1 const& r1, InputRange2 const& r2 ) const
{
// include the standard begin() and end() aswell as any custom overloads for ADL
using std::begin; using std::end;
// Treat null-terminated character arrays, character pointers and ranges uniformly.
// This just creates cheap iterator ranges (it doesn't copy container arguments)!
auto ir1 = boost::as_literal( r1 );
auto ir2 = boost::as_literal( r2 );
// Compare case-insensitively.
return std::lexicographical_compare(
begin( ir1 ), end( ir1 ),
begin( ir2 ), end( ir2 ),
boost::is_iless{} );
}
};
// Case-insensitive set for any Key that consists of a range of characters.
template< class Key, class Allocator = std::allocator<Key> >
using iset = std::set< Key, range_iless, Allocator >;
#include "iset.h" // above header file
#include <iostream>
#include <string>
#include <string_view>
// Output range to stream.
template< typename InputRange, typename Stream, typename CharT >
void write_to( Stream& s, InputRange const& r, CharT const* sep )
{
for( auto const& elem : r )
s << elem << sep;
s << std::endl;
}
int main()
{
iset< std::string > s1{ "Hello", "HELLO", "world" };
iset< std::wstring > s2{ L"Hello", L"HELLO", L"world" };
iset< char const* > s3{ "Hello", "HELLO", "world" };
iset< std::string_view > s4{ "Hello", "HELLO", "world" };
write_to( std::cout, s1, " " );
write_to( std::wcout, s2, L" " );
write_to( std::cout, s3, " " );
write_to( std::cout, s4, " " );
}
#pragma一次
#包括
#包括你能澄清一下“区分大小写插入”的含义吗?当我读到“不区分大小写比较”时,我不禁想起了我的岳母+1.如果字符串中有NUL字符,此方法将无法正常工作。参见.<代码> StimP不是标准C或C++,也不是POSIX或ANSI。它在GCC中不可用,但至少是标准POSIX,并且具有相同的签名。不过,使用std::tolower()
编写您自己的实现非常简单。一句话:如果您使用的是希腊语文本,这将不起作用,因为通常不可能单独使用tolower
实现不区分大小写的比较。教科书中关于这种不可能性的例子是∑∑∑,它不区分大小写,与∑∑∑∑∑(希腊语中的“多达”)相同。
#include "iset.h" // above header file
#include <iostream>
#include <string>
#include <string_view>
// Output range to stream.
template< typename InputRange, typename Stream, typename CharT >
void write_to( Stream& s, InputRange const& r, CharT const* sep )
{
for( auto const& elem : r )
s << elem << sep;
s << std::endl;
}
int main()
{
iset< std::string > s1{ "Hello", "HELLO", "world" };
iset< std::wstring > s2{ L"Hello", L"HELLO", L"world" };
iset< char const* > s3{ "Hello", "HELLO", "world" };
iset< std::string_view > s4{ "Hello", "HELLO", "world" };
write_to( std::cout, s1, " " );
write_to( std::wcout, s2, L" " );
write_to( std::cout, s3, " " );
write_to( std::cout, s4, " " );
}