how to convert mpf_class to String

Question

Hello and sorry for my basic English. I'm trying to convert from mpf_class to a String. I know there is a function (get_str()) but it show me only digits and its exponent separated. I want to get the whole expression in a string. I tried using ostreamstring and it work but I want to know if there is another way to do that. Let me know if I made myself clear.

Basically what I did was:

std::ostringstream show;
mpf_class result, Afact,Bfact,Cfact;
result=Afact*Bfact/Cfact;
show << result;
ui->lineEdit_5->setText(QString::fromStdString(show.str()));

As you can see, I'm working in a QT project and I need to show the result in a QLineEdit and with ostreamstring it works. I just was wondering if there is a gmp function to do that. thanks

Answer 1

Not sure whether this can help you, but you can actually print an mpf_class object and use I/O manipulators on it as a typical float object.

Here is my code

#include <gmpxx.h>
#include <iostream>
#include <iomanip>

int main(void) {
    mpf_class a;
    a = 3141592653589793.2;

    std::cout << a << std::endl;
    // Outputs 3.14159e+15

    std::cout << std::uppercase << std::showpos << std::setprecision(3) << a << std::endl;
    // Outputs +3.14E+15

}

Then you can use an std::ostringstream object instead of std::cout.

Reference: https://gmplib.org/manual/C_002b_002b-Formatted-Output.html