How to Print a Double Value With Full Precision Using Cout

How do I print a double value with full precision using cout?

You can set the precision directly on std::cout and use the std::fixed format specifier.

double d = 3.14159265358979;
cout.precision(17);
cout << "Pi: " << fixed << d << endl;

You can #include <limits> to get the maximum precision of a float or double.

#include <limits>

typedef std::numeric_limits< double > dbl;

double d = 3.14159265358979;
cout.precision(dbl::max_digits10);
cout << "Pi: " << d << endl;

print double with precision 4 using cout [duplicate]

Just try:

#include <iomanip>
...
cout << fixed << setprecision(4);
cout << a << endl;

See here.

Why does std::cout print floats, doubles and long doubles to the same decimal precision? [duplicate]

Values have a fixed precision depending on the type and you can't change it. It's implementation defined. You can only change the precision of the output and there is just one setting for all types of floats. You can't have different output precision for float, double and long double. The default output precision for all types of float is 6.

It's technically not possible to set a different output precision for e.g. float than e.g. double.

There are no overloads for std::setprecision. Each std::basic_ostream can hold only one value for precision.

How to properly print a double to cout in C++

setprecision sets the precision, number of digits.

fixed sets fixed format.

i bet that'll fix it.

How to cout a float/double with dynamic precision?

Assuming I have your definition of dynamic correct something like this should work:

void print(float toPrint, int precision)
{
cout.precision(precision);
cout << toPrint <<endl;
}

cout.precision only changes the precision of the printing, it doesn't actually affect how precise the numbers are. If you print with more digits than your numbers have precision, you will get inaccurate digits.

Of course, cout.precision also only changes the maximum precision of the printing. To force it to print trailing zeros, do something like this:

void print(float toPrint, int precision)
{
cout.precision(precision);
cout << fixed;
cout << toPrint <<endl;
}

The difference between a float and a double is that a double is approximately twice as precise as a float. In general, a float has something like 7 or 8 digits of precision, and a double has 15 or 16 digits of precision.

std::cout print all digits of float value

Assuming that the implementation uses radix 2 for the floating point,

if (std::numeric_limits<T>::radix == 2)

then writing ALL the decimal digits for ALL possible values would require:

std::cout << std::setprecision(std::numeric_limits<T>::digits - std::numeric_limits<T>::min_exponent);

I suspect that the formulation would be the same for radix == 10, but I cannot check this (no implementation at hand).

I wonder why you want to print all the decimals. If it's just to reconstruct the value unchanged, this is not necessary. Using a mixture of scientific notation with a precision std::numeric_limits<T>::max_digits10 should do the job. Otherwise, there are well known algorithm to print just enough decimal digits. They are used in the main REPL languages (see python repr, or how java, javascript, some Smalltalk, etc... print the floating point values), unfortunately, they are not part of a standard C++ library AFAIK.



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