Javatpoint Logo
Javatpoint Logo

fesetround() and fegetround() in C++ and their application

Precision is critical in the fields of scientific computing and numerical analysis. Remarkable effects can arise from minor differences in numerical results, so it becomes imperative to keep control over how floating-point operations round. The two fundamental functions fesetround() and fegetround() in C++ let programmers control the floating-point arithmetic rounding mode. In this article, we will examine these functions, their uses, and the significance of precise control in C++ programming in this post.

How to use fesetround()?

  • The <cfenv> header contains the declaration of the fesetround() function, which is a component of the C++ Standard Library.
  • Within its scope, this function is responsible for determining the rounding direction for floating-point arithmetic operations.
  • When a floating-point operation's result cannot be represented exactly, the rounding mode defines how it should be rounded.


It has the following syntax:

In this case, the intended rounding mode is represented by the integer round_mode. The <cfenv> header defines the round_mode constants, which are the potential values:

  • Moving toward negative infinity, FE_DOWNWARD.
  • To the closest representable value, FE_TONEAREST.
  • To zero, or FE_TOWARDZERO.
  • Moving toward positive infinity, FE_UPWARD.


Let us take a program to illustrate how we can set the rounding mode to FE_DOWNWARD in C++:


fesetround() and fegetround() in C++ and their application


The above program is explained as follows,

  • This C++ software modifies the floating-point operations' rounding mode inside a specified scope by using the <cfenv>
  • The software is told to set the rounding mode to "toward negative infinity" for upcoming floating-point computations by calling the fesetround(FE_DOWNWARD) function.
  • It implies that any outcome of these operations will be rounded to the closest lower value that can be represented.
  • It is important in situations when one must have exact control over rounding, like in financial computations or algorithms where rounding to negative infinity improves accuracy.
  • In the selected scope, the program ends by returning 0, highlighting the transient and local nature of the rounding mode alteration.

How to use fegetround():

  • The main objective of the fegetround() function is to give programmers a way to find out what rounding mode is being used in a program.
  • Fegetround() plays a crucial role in maintaining and eventually regaining the original rounding mode in circumstances where the rounding mode needs to be temporarily changed.


It has the following Syntax:

The function returns an integer that represents the current rounding mode and accepts no parameters (void).

One of the constants defined in the <cfenv> header, such as FE_DOWNWARD, FE_TONEAREST, FE_TOWARDZERO, or FE_UPWARD, corresponds to this return value.


Let us take an example to demonstrate the usage of fegetround() in C++:


fesetround() and fegetround() in C++ and their application


The above program is explained as follows,

  • In this program, the first step is to use <cfenv> to store the original rounding mode in the variable originalRoundingMode using fegetround().
  • After that, it uses the built-in rounding mode to perform floating-point calculations. The software then uses fesetround(FE_DOWNWARD) to set the rounding mode to "toward negative infinity" (FE_DOWNWARD) and carries out further floating-point operations with this altered precision setting.
  • Fesetround(originalRoundingMode) is used to restore the original rounding mode to preserve consistency and prevent unforeseen effects on further computations. In conclusion, the program returns 0.
  • It emphasizes the significance of going back to the initial settings for any further computations and the controlled manipulation of rounding modes within a limited scope.


Numerical Stability in Algorithms:

In the realm of numerical stability, precise control over rounding modes plays a crucial role. Adjusting the rounding method to minimize cumulative errors can significantly enhance the stability of iterative algorithms when tackling nonlinear optimization problems or solving systems of linear equations.

Financial and Scientific computations:

Accuracy in computations is frequently required in financial applications. Rounding mistakes can add up while working with monetary amounts and provide inaccurate outcomes. Programmers can make sure that financial computations are carried out with the required precision by properly configuring the rounding mode.

Cross-Platform Compatibility:

The default rounding modes of various platforms and compilers may vary. Programmers can maintain consistency across different settings and guarantee predictable results regardless of the underlying system by explicitly selecting the rounding mode using fesetround().

Customization for Particular needs:

The rounding behavior of some mathematical computations may need to meet particular needs. For example, user could favor rounding toward zero in statistical applications to minimize bias. Programmers can modify the rounding mode to make their code behave in a way that satisfies these needs.

Testing and Debugging:

Rounding problems can be difficult to debug in intricate numerical applications. Through the use of fesetround() to dynamically modify the rounding mode and then query it, programmers can identify and isolate code segments that may have precision problems, which can aid in debugging.


In conclusion, precision is critical in the fields of scientific and financial computers. The C++ fesetround() and fegetround() methods give programmers the ability to regulate how floating-point arithmetic rounds, ensuring that calculations are completed with the appropriate degree of accuracy. Developers can improve the accuracy and dependability of their numerical algorithms and strengthen the code's resilience across various platforms and applications by comprehending and utilizing these functions.

Youtube For Videos Join Our Youtube Channel: Join Now


Help Others, Please Share

facebook twitter pinterest

Learn Latest Tutorials


Trending Technologies

B.Tech / MCA