I would like to check the value of the 5th and the 4th bit starting from the left in this strings like this one:

value: "00001101100000000000000001000110"

value: "00000101100000000000000001000110" 

value: "00010101100000000000000001000110"

The value is generated as a string in this way:

        msg.value = bitset<32>(packet.status()).to_string();

to be sent a a ROS node and I receive it as a string. Can I still use bitset to check the value of the bits even if it is a string? What is the best solution to check them?

CodePudding user response：

You don't have a bitset, you have a string, in which each "bit" is represented by a char.

To check the 4th and 5th "bits", just use:

1. msg.value[3] != '0' and msg.value[4] != '0'

2. msg.value[3] & 1 and msg.value[4] & 1

#2 might be faster; it exploits the fact that '0' and '1' differ in the lowest bit only.

CodePudding user response：

Just create the bitset on its own, do the tests and then make a string out of it. (Or recreate a bitset from the string and test on that)

#include <bitset>
#include <string>
#include <iostream>

struct msg_t
{
    std::string value;
};

struct packet_t
{
    std::string status()
    {
        return "00001101100000000000000001000110";
    }
};

int main()
{
    packet_t packet;
    auto bits = std::bitset<32>(packet.status());
    bool bit4 = bits.test(4);
    bool bit5 = bits.test(5);

    if (bit4) std::cout << "bit 4 is set\n";
    if (bit5) std::cout << "bit 5 is set\n";

    msg_t msg;
    msg.value = bits.to_string();

    return 0;
}