I use pugi::XML parser and i want to set the precision for the floating point numbers. I have already used the rounding function on the float variable, but while printing with pugi::xml, it is printed with 6 decimal digits.
I use below statement to print value in C++11 :
subNode.append_child(pugi::node_pcdata).set_value(to_string(doubleVal).c_str());
Example:
<value>97.802000</value>
must be printed as
<value>97.802</value>
How can i do that ?
Try this:
#include <iomanip> // setprecision
#include <sstream> // stringstream
std::string toStringPrecision(double input,int n)
{
stringstream stream;
stream << std::fixed << setprecision(n) << input;
return stream.str();
}
Then you call it in:
subNode.append_child(pugi::node_pcdata).set_value(toStringPrecision(doubleVal,3).c_str());
Related
I'm trying to get value (all decimal number) from a text in c++. But I have a problem and I couldn't solve it
#include "pch.h"
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
int main()
{
std::ifstream infile("C:\\thefile.txt");
float a, b;
while (infile >> a >> b)
{
// process pair (a,b)
}
std::cout << a << " " << b;
}
thefile.txt:
34.123456789 77.987654321
When I run the above code,
a = 34.1235
b = 77.9877
but I want
a = 34.123456789
b = 77.987654321
what should I do?
EDIT: I don't want to print out of a and b. I just want they get the exact values.net
You can't.
A float can only give you six (ish) decimal significant figures. The values in your file, after conversion from string, cannot be held in a float.
First, you need to switch to double, otherwise you won't even have a variable with the full numerical value.
Then, for output, be careful to specify the precision you want.
Please remain aware of the foibles of floating-point, and consider sticking with strings, depending on what you're doing with this data.
There are two main things i see in your code.
float precision is not enough for you data you need double data type.
you need to set proper cout precision to get your desired output.
This code will work for you.
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
int main()
{
std::ifstream infile("newfile.txt");
double a, b;
std::cout.precision(11);
while (infile >> a >> b)
{
// process pair (a,b)
}
std::cout << a << " " << b;
}
you should read your inputs into a string and then convert them into double (depending on enough precision in float on your computer). you can directly display strings. A possible answer is here.
string word;
openfile >> word;
double lol = atof(word.c_str());
1)double d = 1.234567899;
Convert this number to string with 8 decimal places without truncation.
So,expected output is "1.23456789", truncating last 9.
and
2)if d = 1.2345699;
so Solution should not append 0 upto 8th decimal place.expected output "1.2345699".
I have tried many solutions,ended up with stringstream c++ class. 2nd problem is solved but first one still persist.
Is there any way to achieve the output?
Thanks in advance.
If you want to truncate part of the string representation without rounding, you need to do that manually:
#include <iostream>
#include <sstream>
#include <string>
#include <iomanip>
#include <limits>
int main()
{
std::stringstream s;
double d = 1.234567899;
// print it into sstream using maximum precision
s << std::fixed << std::setprecision(std::numeric_limits<double>::digits10) << 1.234567899;
std::string res = s.str();
// Now the res contains something like 1.234567899000000
// so truncate 9000000000 by hand
size_t dotIndex = res.find(".");
std::string final_res = res.substr(0, dotIndex + 9);
std::cout << final_res << std::endl;
return 0;
}
Would you be served by first Flooring the double to the required decimals?
If so, have a look at http://www.cplusplus.com/forum/beginner/3600/
Truncating exactly as you want:
sprintf(str, "%1.10f", d);
memset(str+10, 0x00, 1);
I' d like to use lexical_cast to convert a float to a string. Usually it works fine, but I have some problems with numbers without decimal. How can I fix number of decimal shown in the string?
Example:
double n=5;
string number;
number = boost::lexical_cast<string>(n);
Result number is 5, I need number 5.00.
From the documentation for boost lexical_cast:
For more involved conversions, such as where precision or formatting need tighter control than is offered by the default behavior of lexical_cast, the conventional stringstream approach is recommended. Where the conversions are numeric to numeric, numeric_cast may offer more reasonable behavior than lexical_cast.
Example:
#include <sstream>
#include <iomanip>
int main() {
std::ostringstream ss;
double x = 5;
ss << std::fixed << std::setprecision(2);
ss << x;
std::string s = ss.str();
return 0;
}
Have a look at boost::format library. It merges the usability of printf with type safety of streams. For speed, I do not know, but I doubt it really matters nowadays.
#include <boost/format.hpp>
#include <iostream>
int main()
{
double x = 5.0;
std::cout << boost::str(boost::format("%.2f") % x) << '\n';
}
If you need complex formatting, use std::ostringstream instead. boost::lexical_cast is meant for "simple formatting".
std::string
get_formatted_value(double d) {
std::ostringstream oss;
oss.setprecision(3);
oss.setf(std::ostringstream::showpoint);
oss << d;
return oss.str();
}
you can also use sprintf, which is faster then ostringstream
#include <cstdio>
#include <string>
using namespace std;
int main()
{
double n = 5.0;
char str_tmp[50];
sprintf(str_tmp, "%.2f", n);
string number(str_tmp);
}
Is there a built in function in c++ that can handle converting a string like "2.12e-6" to a double?
strtod()
atof should do the job. This how its input should look like:
A valid floating point number for atof is formed by a succession of:
An optional plus or minus sign
A sequence of digits, optionally containing a decimal-point character
An optional exponent part, which itself consists on an 'e' or 'E' character followed by an optional sign and a sequence of digits.
If you would rather use a c++ method (instead of a c function)
Use streams like all other types:
#include <iostream>
#include <sstream>
#include <string>
#include <iterator>
#include <boost/lexical_cast.hpp>
int main()
{
std::string val = "2.12e-6";
double x;
// convert a string into a double
std::stringstream sval(val);
sval >> x;
// Print the value just to make sure:
std::cout << x << "\n";
double y = boost::lexical_cast<double>(val);
std::cout << y << "\n";
}
boost of course has a convenient short cut boost::lexical_cast<double> Or it is trivial to write your own.
The conversion i wrote of hexadecimal to decimal number is working but get some little bit unexpected result.
Expected result : HEX number "0000000F" and Output is in Decimal "15"
In my case
1] if "0000000F" is HEX value and it's conversion is "1532"
2] if "000000FF" is HEX value and it's conversion is "25532"
I am not sure what part of programming is wrong ? every time I get "32" After any decimal value result. Can Anyone suggest how to fix this issue ?
#include <iostream>
using namespace std ;
#include <sstream>
int wmain() {
while(1)
{
int binNumber ;
unsigned int decimal;
string hexString = "0000000F"; //you may or may not add 0x before
stringstream myStream;
myStream <<hex <<hexString;
myStream >>binNumber;
cout <<binNumber <<decimal;
//return 0;
}
}
If you look at the first parts of your outputs, you will notice that they are correct.
But here:
cout <<binNumber <<decimal;
you're printing decimal immediately afterwards, and it is uninitialised.
Remove it.
(On a related note, don't declare variables that you think you might need at some point in the future. Many bugs lurk down that way.)
// Correct code
#include <iostream>
using namespace std ;
#include <sstream>
int wmain() {
while(1)
{
int binNumber ;
// unsigned int dummy=0;
string hexString = "000000FF"; //you may or may not add 0x before
stringstream myStream;
myStream <<hex <<hexString;
myStream >>binNumber;
cout <<binNumber ;
//return 0;
}
}