我可能偶然发现了一个bug,但可能只是他们实现标准库的方式。以下是bug吗?
在gcc 4.8.2和clang 3.4中,如果我在一个只有一个元素的map上使用std::map::lower_bound(),它会返回end(),即使map中的元素是一个下界。
如果您要测试此功能,请务必使用下列编译选项:- 标准品=c++11
#include <cstdlib>
#include <iostream>
#include <map>
#define ts_t std::pair<uint64_t,uint64_t>
int main() {
std::map<ts_t,uint32_t> test;
uint32_t count = 0;
test.insert(std::make_pair(
std::make_pair(1403187740ull,698599ull),
count++
));
ts_t key = std::make_pair(1403187740ull,698600ull);
auto lower = test.lower_bound(key);
auto upper = test.upper_bound(key);
if(lower==test.end()) std::cout<<"no lower bound\n";
if(upper==test.end()) std::cout<<"no upper bound\n";
if(test.begin()->first < key) std::cout<<"key is less than begin()\n";
test.insert(std::make_pair(
std::make_pair(1403187740ull,698601ull),
count++
));
lower = test.lower_bound(key);
upper = test.upper_bound(key);
if(lower==test.end()) std::cout<<"no lower bound\n";
if(upper==test.end()) std::cout<<"no upper bound\n";
if(test.begin()->first < key) std::cout<<"key is less than begin()\n";
return EXIT_SUCCESS;
}
下面是我得到的输出:
no lower bound
no upper bound
key is less than begin()
key is less than begin()
我期望看到:
no upper bound
key is less than begin()
key is less than begin()
**更新:**在回答后,我写了这个更新的代码,它确实完成了我所追求的。我把它贴在这里,以防其他人试图完成同样的事情:
#include <cstdlib>
#include <iostream>
#include <map>
#define ts_t std::pair<uint64_t,uint64_t>
int main() {
std::map<ts_t,uint32_t> test;
uint32_t count = 0;
test.insert(std::make_pair(
std::make_pair(1403187740ull,698599ull),
count++
));
ts_t key = std::make_pair(1403187740ull,698600ull);
std::map<ts_t,uint32_t>::iterator upper = test.upper_bound(key);
std::map<ts_t,uint32_t>::iterator lower;
if(upper==test.begin()){
lower = test.end();
} else {
lower = upper;
--lower;
}
if(lower==test.end()) std::cout<<"no lower key\n";
if(upper==test.end()) std::cout<<"no upper bound\n";
if(test.begin()->first < key) std::cout<<"key is less than begin()\n";
test.insert(std::make_pair(
std::make_pair(1403187740ull,698601ull),
count++
));
lower = test.lower_bound(key);
upper = test.upper_bound(key);
if(lower==test.end()) std::cout<<"no lower key\n";
if(upper==test.end()) std::cout<<"no upper bound\n";
if(test.begin()->first < key) std::cout<<"key is less than begin()\n";
return EXIT_SUCCESS;
}
1条答案
按热度按时间wmtdaxz31#
你误解了
lower_bound
的意思。它并不意味着它下面的元素;它意味着不小于即大于或等于的第一个元素。此函数的目的是使范围
lower_bound
,upper_bound
与等于搜索关键字的所有元素匹配。