Is There a Built-in Round Function in C and How Can I Implement One?

Rounding Floating-Point Values in C

The question arises as to whether the standard C library includes a function named round() to facilitate the rounding of floating-point values. Despite the presence of ceil() and floor() in the math.h header, round() remains absent.

Implementing a Rounding Function

Although round() is not natively available in the C 98 standard library, its implementation is relatively straightforward. Here's an example of a round-half-up function:

double round(double d) {
  return floor(d + 0.5);
}

This implementation calculates the rounded value by adding 0.5 to the input, then applying the floor function to truncate the result.

Reason for Its Absence in the C 98 Standard Library

The omission of round() from the C 98 standard likely stems from the fact that it can be implemented in various ways. The round-half-up approach is commonly used, but other rounding methods, such as round-to-even, exist. Implementing these different approaches adds complexity to the standard library.

Modern C Solutions

C 11 introduced built-in round() functions: std::round, std::lround, and std::llround. These provide a more robust and efficient way to perform rounding operations on floating-point values.

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