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
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
Related
I want to take in persons name using string object. But in my code if I put two part name separated with a space, only first part is displayed. My understanding is .c_str() returns a pointer to stored string with terminal null. Why is there a problem with space. I'm new to C++ and using Code::Blocks 13.12. This is a simplified version of the problem that I have in another program that I wrote.
Thanks in advance.
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cstring>
#include <string>
using namespace std;
int main()
{
string sCusName;
cout << "Please enter your name-> ";
cin >> sCusName;
int xsize = sCusName.length();
char *tempBuffer = new char[xsize+1];
strncpy(tempBuffer, sCusName.c_str(),xsize+1);
cout << tempBuffer << " is a beautiful name." << endl;
return 0;
}
When I enter single part name, program works fine. But if I put in two part name separated with space. Only first part is taken in.
it is not possible to read multi-word string using cin rather you should use getline() the getline() function takes two arguments cin and string variable forexample:
int main()
{
string sCusName;
cout << "Please enter your name-> ";
getline(cin,sCusName);
cout << sCusName << " is a beautiful name." << endl;
return 0;
}
I am trying to understand, then, write some code that has to read from, and write to many different files and do so from the main loop of my application. I am hoping to use the C++11 model present in VS 2013.
I don't want to stall the main loop so I am investigating spinning off a thread each time a request to write or read a file is generated.
I've tried many things including using the async keyword which sounds promising. I boiled down some code to a simple example:
#include <future>
#include <iostream>
#include <string>
bool write_file(const std::string filename)
{
std::cout << "write_file: filename is " << filename << std::endl;
std::this_thread::sleep_for(std::chrono::milliseconds(2000));
std::cout << "write_file: written" << std::endl;
return true;
}
int main(int argc, char* argv[])
{
const std::string filename = "foo.txt";
auto write = std::async(std::launch::async, write_file, filename);
while (true)
{
std::cout << "working..." << std::endl;
std::this_thread::sleep_for(std::chrono::milliseconds(100));
std::cout << "write result is " << write.get() << std::endl;
}
}
I'm struggling to understand the basics but my expectation would be that this code would constantly print "working..." and interspersed in the output would be the write_file start and end messages. Instead, I see that the write_file thread seems to block the main loop output until the timer expires.
I realize I need to also consider mutex/locking on the code to actually write the file but I would like to understand this bit first.
Thank you if you can point me in the right direction.
Molly.
write.get() will wait for the async task to finish. You want to use wait_for() instead:
do {
std::cout << "working...\n";
} while(write.wait_for(std::chrono::milliseconds(100)) != std::future_status::ready);
std::cout << "write result is " << write.get() << "\n";
I am working on a money program. Currently I am trying to make a part in the program that displays a list that shows every transaction that was made in the session. My problem is that when I convert the money amount to a string instead of displaying something like 100.35 in when converted to a string it instead displays something like 100.35000000. I was wondering if there was any way I could make the program drop the additional zeros? Here is a sample of how I convert the numbers to a string
int main(){
double samplemoney=100.35;
string sample="Today we made $";
string comsample;
comsample=sample+std::tostring(money)+".";
cout<<comsample<<endl;
return 0;
}
In my main program this part is handled with a class but as I said earlier it seems like no matter what the money value I put in is it will display a series of zero and I want my program to drop the unnecessary zeros.
Let's say you have this number:
double number = 190.0391000;
If the problem is displaying the value you may use
std::cout << std::setprecision(5) << number
where f is the number you want to show.
If your problem is having a string with a finite precision you can use sprintf() in the following way:
char arr[128];
sprintf(arr,"%3.2f", number);
std::string formattedstring(arr);
or in a more C++ oriented way something like this
std::stringstream strn;
strn.precision(2);
strn << std::fixed << number;
and then you get the string in the following way:
std::string formattedstring = strn.str();
I attach the full text of program here... tested on my machine:
#include <sstream>
#include <iostream>
int main() {
float number=100.24324232;
std::stringstream strn;
strn.precision(2);
strn << std::fixed << number;
std::cout << strn.str() << "\n";
return( 0 );
}
So I'm starting a book called " Beginning c++ Through Game Programming, third edition, by Michael Dawson" and the very fist program I tried to run didn't work. I even tried just using the source code. Here it is:
// Game Over
// A first C++ program
#include <iostream>
int main()
{
std::cout << "Game Over!" << std::endl;
return 0;
}
If this is what you see, just check the checkbox at the bottom and hit "Yes". That will keep it from popping up. It's not an error in your code.
Otherwise, you need to post the error message you are receiving.
Based on various comments I'd made for the default of pre-compiled headers under VC++ and to leave the window open until enter is pressed use the following:
#include "stdafx.h"
#include <iostream>
int main()
{
std::cout << "Game Over!" << std::endl;
cin.ignore();
return 0;
}
I have a straightforward problem but I don't understand why I have it.
I would greatly appreciate any insight.
I wrote this code to test that I was correctly creating and using DLLs in Visual Studio 2010 under Win 7 64bit that could execute on Windows XP. The code executes correctly, and because it is a small test program freeing the allocated memory is not critical, but certainly will be in the future.
I am implicitly calling the DLL, as I say, it appears to work just fine. When I add the line "delete dllMsg;" to toyUseDLL.cpp it crashes, and the debugger shows _unlock_fhandle in osfinfo.c.
If it's relevant I am compiling the program with /MT to embed the runtime library (for a small handful of not important reasons).
It seems pretty obvious that I'm deallocating something not allocated, but the program output is correct since the pointers are passing the referenced memory locations. The only thing I can think of is that my pointer isn't valid, and it's only working by pure chance that the memory wasn't overwritten.
Thanks for any help, I'm pretty new to C++ and have already found a lot of great help on this site, so thanks for everyone who has posted in the past!! :-)
msgDLL.h
#include <string>
using namespace std;
namespace toyMsgs {
class myToyMsgs {
public:
static __declspec(dllexport) string* helloMsg(void);
static __declspec(dllexport) string* goodbyeMsg(void);
};
}
msgDLL.cpp
#include <iostream>
#include <string>
#include "msgDLL.h"
using namespace std;
namespace toyMsgs {
string* myToyMsgs::helloMsg(void) {
string *dllMsg = new string;
dllMsg->assign("Hello from the DLL");
cout << "Here in helloMsg, dllMsg is: \"" << *(dllMsg) << "\"" << endl;
return (dllMsg);
}
string* myToyMsgs::goodbyeMsg(void) {
string *dllMsg = new string;
dllMsg->assign("Good bye from the DLL");
cout << "Here in goodbyeMsg, dllMsg is: \"" << *(dllMsg) << "\"" << endl;
return (dllMsg);
}
}
toyUseDLL.cpp
#include <iostream>
#include <string>
#include "stdafx.h"
#include "msgDLL.h"
using namespace std;
int _tmain(int argc, _TCHAR* argv[]) {
string myMsg;
string *dllMsg;
myMsg.assign ("This is a hello from the toy program");
cout << myMsg << endl;
dllMsg = toyMsgs::myToyMsgs::helloMsg();
cout << "Saying Hello? " << *(dllMsg) << endl;
delete dllMsg;
myMsg.assign ("This is the middle of the toy program");
cout << myMsg << endl;
dllMsg = toyMsgs::myToyMsgs::goodbyeMsg();
cout << "Saying goodbye? " << *(dllMsg) << endl;
myMsg.assign ("This is a goodbye from the toy program");
cout << myMsg << endl;
return 0;
}
Program Output:
This is a hello from the toy program
Here in helloMsg, dllMsg is: "Hello from the DLL"
Saying Hello? Hello from the DLL
This is the middle of the toy program
Here in goodbyeMsg, dllMsg is: "Good bye from the DLL"
Saying goodbye? Good bye from the DLL
This is a goodbye from the toy program
The problem is that you are using /MT to compile your EXE and DLL. When you use /MT, each executable gets its own copy of the C runtime library, which is a separate and independent context. CRT and Standard C++ Library types can't safely be passed across the DLL boundary when both DLLs are compiled /MT. In your case the string is allocated by one CRT (on its private OS Heap), and freed by the EXE (which has a different heap) causing the crash in question.
To make the program work, simply compile /MD.
General advice: /MT is almost never the right thing to do (for a large handful of relatively important reasons including memory cost, performance, servicing, security and others).
Martyn
There is some good analysis here Why does this program crash: passing of std::string between DLLs