Syntax of C++ setprecision
setprecision(int n);
Here, the argument n decides the total number of a significant figure in the given integer. This parameter is of integer type, and it is a necessary parameter.
How SetPrecision in C++ Works?

std::setprecision is a manipulator in C++ that affects the precision of floatingpoint output in streams.
 It is part of the <iomanip> header in the C++ Standard Library.
 When used with std::cout, it sets the number of digits to display after the decimal point for floatingpoint values.
 It takes an integer argument specifying the desired precision.
 The precision affects both fixedpoint notation and scientific notation.
 If precision is set to n, it guarantees that at least n digits are displayed in total, including digits before and after the decimal point.
 The actual behavior may depend on the floatingpoint representation used by the system.
Parameters of C++ setprecision
The setprecision function expects a single integer parameter ‘n’ that specifies the desired precision.

If ‘n' is zero:
The number is rounded off to the nearest integer.

If ‘n’ is 1:
The default precision is used.

Otherwise,
Depending upon the formatting, the number of digits before and after the decimal is restricted to n.
Return Value of C++ setprecision
setprecision doesn't return any values, it is only used for manipulating the input/output streams to modify the formatting of decimal numbers.
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Exceptions of C++ iomanip setprecision() function
The std::setprecision function behaves depending upon the formatting of the stream. It is important to use setprecision according to the formatting set using std::fixed, std::scientific, std::defaultfloat, std::showpoint, etc.
The following code in C++ illustrates the changing behavior of setprecision() function depending on the selected formatting.
C++
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double num = 1013.4567;
cout << setprecision(2);
cout << showpoint << num << "\n";
cout << fixed << num << "\n";
cout << defaultfloat << num << "\n";
cout << scientific << num << "\n";
}
Output:
1.0e+03
1013.46
1.0e+03
1.01e+03
Significant Figures and Decimal Places
Significant figures in a number carry information related to the precision of that value. They represent the number of reliable values in a measured value or result. All nonzero digits and zeros between nonzero digits are significant while leading zeros are not considered significant digits.
For example:
456 has 3 significant digits
0.0003 has 1 significant digit
101 has 3 significant digits
Decimal places indicate the number of digits present in a number after the decimal.
For example:
456.123 has 3 decimal places
2.00 has 2 decimal places
Examples of C++ setprecision function
Example 1: Using std::setprecision() function
C++
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double num = 1013.4567;
cout << setprecision(2) << num << "\n";
}
Output:
1.0e+03
In this example, setprecision applies a significant figure limit of 2 on both before and after the decimal combined as the default formatting is used.
Example 2: Default Precision and Maximum Precision
C++
#include <iostream>
#include <iomanip>
#include <limits>
using namespace std;
int main () {
double e = 2.718281828459045;
cout<< "Default precision: " << e << "\n";
cout<< "Max precision : " << setprecision(numeric_limits<double>::digits10 + 1) << e << "\n";
return 0;
}
Output:
Default precision: 2.71828
Max precision : 2.718281828459045
The default precision is 6 which limits the total number of significant figures before and after the decimal.
Example 3: Using std::fixed to Set Precision in Decimal Places
C++
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double num = 1013.4567;
cout << setprecision(2);
cout << fixed << num << "\n";
}
Output:
1013.46
std::fixed changes formatting of the input/output stream to fixed from std::defaultfloat which is the default formatting in C++.
Example 4: Using std::fixed to find default precision and maximum precision
C++
#include <iostream>
#include <iomanip>
#include <limits>
using namespace std;
int main () {
double e = 2.718281828459045;
cout << fixed;
cout<< "Default precision: " << e << "\n";
cout<< "Max precision : " << setprecision(numeric_limits<double>::digits10 + 1) << e << "\n";
return 0;
}
Output:
Default precision: 2.718282
Max precision : 2.7182818284590451
In the above example, the default precision of 6 is applied to the digits after the decimal, without fixed formatting, only 5 digits after the decimal would have been printed.
Where and how can we use setprecision in C++?
To format our output in floatingpoint numbers, we use setprecision in C++. Here, if we use the “fixed” keyword before setprecision then the parameter decides only the count after the decimal point else it considers the significant figure.
Note: setprecision in C++ gives a roundoff value.
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Frequently Asked Questions
What does fixed and Setprecision do in C++?
In C++, `fixed` and `setprecision` format output. `fixed` ensures that floatingpoint numbers are displayed in fixedpoint notation, while `setprecision` sets the number of decimal places.
What is Setprecision in C++ 11?
`setprecision` in C++ 11 is a function from the `<iomanip>` library that allows you to set the precision (number of decimal places) for floatingpoint output.
What is the difference between Setw and Setprecision in C++?
`setw` is used to set the field width for output formatting in C++, while `setprecision` is used to set the precision (decimal places) for floatingpoint numbers.
Which library is Setprecision in C++?
`setprecision` is a function provided by the `<iomanip>` library in C++ to control the precision (number of decimal places) for floatingpoint output.
Does Setprecision affect integers?
No, `setprecision` in C++ specifically affects the formatting of floatingpoint numbers and does not impact the formatting of integers.
What is the default precision in C++?
The default precision in C++ is 6 significant digits.
What is the difference between fixed and Setprecision in C++?
std::fixed and std::setprecision are both stream manipulators which are part of the iomanip header file in GCC. std::fixed changes the formatting of the I/O stream to fixed. Meanwhile, std::setprecision is used for setting the number of digits to be displayed before and after the decimal depending on the formatting.
Conclusion
In this article, we have discussed the details of the method set::precision in C++ with examples.
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