In c++. I initialize a bitset to -3 like:
std::bitset<32> mybit(-3);
Is there a grace way that convert mybit to -3. Beacause bitset object only have methods like to_ulong and to_string.
2 Answers
Use to_ulong to convert it to unsigned long, then an ordinary cast to convert it to int.
int mybit_int;
mybit_int = (int)(mybit.to_ulong());
7 Comments
Steve
As this is C++ I would suggest using static_cast<int>(mybit.to_ulong()) rather than a C-style cast.
FluorescentGreen5
not working, still spitting out unsigned integer. -3 is becoming 251
Barmar
@FluorescentGreen5 I've added a demo showing that it works.
Barmar
@ErkinAlpGüney I think his suggestion is about style -- in C++ you should use the template syntax rather than the C syntax for casts, because it makes your intent clearer. But I'm not that much of a purist, and I find the verbose syntax off-putting.
Steve
@ErkinAlpGüney - my suggestion is about safety of the operation. If you use a
static_cast the code is more resilient to someone coming in and changing types. stackoverflow.com/a/103868/1517648 I've seen various occasions where C-style casts were ok, until someone changed something and then they weren't. A static_cast would pick this up with a compiler error. |
One comple example worked for both 32bit and not-32bit bitsets
#include <bitset>
#include <iostream>
template<std::size_t SIZE>
int bitSetToInt(std::bitset<SIZE> bitSet) {
if (!bitSet[SIZE - 1]) return bitSet.to_ulong();
bitSet.flip();
return -(bitSet.to_ulong() + 1);
}
int main() {
std::bitset<31> bitSet1(7);
std::bitset<31> bitSet2(-7);
std::bitset<32> bitSet3(7);
std::bitset<32> bitSet4(-7);
std::cout << bitSet1 << " = " << bitSetToInt(bitSet1) << std::endl;
std::cout << bitSet2 << " = " << bitSetToInt(bitSet2) << std::endl;
std::cout << bitSet3 << " = " << bitSetToInt(bitSet3) << std::endl;
std::cout << bitSet4 << " = " << bitSetToInt(bitSet4) << std::endl;
}
Output
0000000000000000000000000000111 = 7
1111111111111111111111111111001 = -7
00000000000000000000000000000111 = 7
11111111111111111111111111111001 = -7
The dynamic version
#include <iostream>
#include <boost/dynamic_bitset.hpp>
int dynamicBitSetToInt(boost::dynamic_bitset<> bitSet) {
if (!bitSet[bitSet.size() - 1]) return (int) bitSet.to_ulong();
bitSet.flip();
return (int) -(bitSet.to_ulong() + 1);
}
int main() {
boost::dynamic_bitset bitSet1(31, 7);
boost::dynamic_bitset bitSet2(31, -7);
boost::dynamic_bitset bitSet3(32, 7);
boost::dynamic_bitset bitSet4(32, -7);
std::cout << bitSet1 << " = " << dynamicBitSetToInt(bitSet1) << std::endl;
std::cout << bitSet2 << " = " << dynamicBitSetToInt(bitSet2) << std::endl;
std::cout << bitSet3 << " = " << dynamicBitSetToInt(bitSet3) << std::endl;
std::cout << bitSet4 << " = " << dynamicBitSetToInt(bitSet4) << std::endl;
}
std::bitsethas function to convert the value to a ulong. So as @Barmar says, cast that long to a int. So whats your problem? Have you readed the documentation or tried anything before posting the question?ulongtolong, theninti.e.int(long(mybit.to_ulong()))