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| Member types | ||||
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(until C++20) | ||||
| Element access | ||||
bitset::test | ||||
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(C++11) | ||||
bool test(std::size_t pos)const; | (constexpr since C++23) | |
Returns the value of the bit at the positionpos (counting from 0).
Unlikeoperator[], it performs a bounds check.
Contents |
| pos | - | position of the bit to return (counting from 0) |
true if the requested bit is set,false otherwise.
Throwsstd::out_of_range ifpos does not correspond to a valid bit position.
#include <bit>#include <bitset>#include <cassert>#include <iostream>#include <stdexcept> int main(){std::bitset<10> b1("1111010000"); std::size_t idx=0;while(idx< b1.size()&&!b1.test(idx))++idx; assert(static_cast<int>(idx)==std::countr_zero(b1.to_ulong())); if(idx< b1.size())std::cout<<"The first set bit is at index "<< idx<<'\n';elsestd::cout<<"no set bits\n"; try{std::bitset<0B10'1001'1010> bad;if(bad.test(bad.size()))std::cout<<"Expect unexpected!\n";}catch(std::out_of_rangeconst& ex){std::cout<<"Exception: "<< ex.what()<<'\n';}}
Possible output:
The first set bit is at index 4Exception: bitset::test: __position (which is 666) >= _Nb (which is 666)
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2250 | C++98 | the behavior was undefined ifpos does not correspond to a valid bit position | always throws an exception in this case |
| accesses specific bit (public member function)[edit] | |
(C++20) | counts the number of1 bits in an unsigned integer (function template)[edit] |
(C++20) | checks if a number is an integral power of2 (function template)[edit] |
