What is RF() here? Is it absolutely necessary here? - c++

Question

class RF
{
public:
bitset<32> ReadData1, ReadData2;
RF()
{
Registers.resize(32);
Registers[0] = bitset<32> (0);
}
void ReadWrite(bitset<5> RdReg1, bitset<5> RdReg2, bitset<5> WrtReg, bitset<32> WrtData, bitset<1> WrtEnable)
{
// implement the funciton by you.
}
void OutputRF() // write RF results to file
{
ofstream rfout;
rfout.open("RFresult.txt",std::ios_base::app);
if (rfout.is_open())
{
rfout<<"A state of RF:"<<endl;
for (int j = 0; j<32; j++)
{
rfout << Registers[j]<<endl;
}
}
else cout<<"Unable to open file";
rfout.close();
}
private:
vector<bitset<32> >Registers;
};

Answer 1

RF() is the constructor, but since all it does is resize Registers to 32, you can remove it if you specify that initialization on the member directly, like this:
vector<bitset<32> > Registers = vector<bitset<32> >(32);
Then Registers will be constructed with size 32x32 bits by default, and all the bits will be zero as well, so you can remove the entire RF() function.
Note: At first I thought you could use vector<bitset<32> > Registers{32} but due to vagaries of C++ syntax that does the wrong thing. Thanks to Fureeish for that.

Answer 2

The short answer to your question is that, yes, for your current program, it is necessary.
The RF() function in this case is the function called when we initialize the RF object, eg.
RF new_RF;
Would run the RF() function and set things up. For this reason, it is called a 'constructor', because it helps you 'construct' your class.
In your case, the constructor is necessary for your program because it sets up your Registers variable, so that the code below from your OutputRF() function can run.
for (int j = 0; j<32; j++)
{
rfout << Registers[j]<<endl;
}
It's also useful because we can use it to set up many things, for example, if our RF() constructor looked like this:
RF(int a)
{
Registers.resize(a);
Registers[0] = bitset<a> (0);
}
It would instead resize the RF Registers to int a. You can look here for a more in-depth tutorial about constructors.
Hope that helps!