C/C++ function round

你的名字 2022-10-23 05:55 3阅读 0赞

# **C/C++ function `round`** #

## 1. Round to nearest ##

Returns the integral value that is nearest to `x`, with halfway cases rounded away from zero.  
返回最接近 `x` 的整数值，中间情况从零舍入。

### 1.1 C99 ###

double round  (double x);
          float roundf (float x);
    long double roundl (long double x);

Header `<tgmath.h>` provides a type-generic macro version of this function.

### 1.2 C++11 ###

double round (double x);
          float round (float x);
    long double round (long double x);
         double round (T x);           // additional overloads for integral types

Additional overloads are provided in this header (`<cmath>`) for the integral types: These overloads effectively cast x to a double before calculations (defined for `T` being any integral type).  
在此头文件 (`<cmath>`) 中，还为整数类型提供了其他重载：这些重载有效地在计算前将 x 强制转换为 double (为 `T` 定义为任何整数类型)。

## 2. Parameters ##

`x` \- Value to round.

## 3. Return Value ##

The value of `x` rounded to the nearest integral (as a floating-point value).  
`x` 的值四舍五入到最接近的整数 (作为浮点值)。

## 4. Example ##

//============================================================================
    // Name        : Yongqiang Cheng
    // Author      : Yongqiang Cheng
    // Version     : Version 1.0.0
    // Copyright   : Copyright (c) 2020 Yongqiang Cheng
    // Description : Hello World in C++, Ansi-style
    //============================================================================
    
    #ifndef _CRT_SECURE_NO_WARNINGS
    #define _CRT_SECURE_NO_WARNINGS
    #endif
    
    /* round vs floor vs ceil vs trunc */
    #include <stdio.h>      /* printf */
    #include <math.h>       /* round, floor, ceil, trunc */
    
    int main()
    {
    	const char * format = "%.1f \t%.1f \t%.1f \t%.1f \t%.1f\n";
    
    	printf("value\tround\tfloor\tceil\ttrunc\n");
    	printf("-----\t-----\t-----\t----\t-----\n");
    
    	printf(format, 2.3, round(2.3), floor(2.3), ceil(2.3), trunc(2.3));
    	printf(format, 3.8, round(3.8), floor(3.8), ceil(3.8), trunc(3.8));
    	printf(format, 5.5, round(5.5), floor(5.5), ceil(5.5), trunc(5.5));
    	printf(format, -2.3, round(-2.3), floor(-2.3), ceil(-2.3), trunc(-2.3));
    	printf(format, -3.8, round(-3.8), floor(-3.8), ceil(-3.8), trunc(-3.8));
    	printf(format, -5.5, round(-5.5), floor(-5.5), ceil(-5.5), trunc(-5.5));
    
    	return 0;
    }

value   round   floor   ceil    trunc
    -----   -----   -----   ----    -----
    2.3     2.0     2.0     3.0     2.0
    3.8     4.0     3.0     4.0     3.0
    5.5     6.0     5.0     6.0     5.0
    -2.3    -2.0    -3.0    -2.0    -2.0
    -3.8    -4.0    -4.0    -3.0    -3.0
    -5.5    -6.0    -6.0    -5.0    -5.0
    请按任意键继续. . .

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXExMTY_size_16_color_FFFFFF_t_70_pic_center]

## References ##

[http://www.cplusplus.com/reference/cmath/round/][http_www.cplusplus.com_reference_cmath_round]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXExMTY_size_16_color_FFFFFF_t_70_pic_center]: /images/20221023/1f92a5496f1a488dae087e164c7b4d65.png
[http_www.cplusplus.com_reference_cmath_round]: http://www.cplusplus.com/reference/cmath/round/