C语言 ceil函数在C中的实现
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Implementation of ceil function in C
提问by AGeek
I have two questions regarding ceil()function..
我有两个关于ceil()函数的问题..
The
ceil()function is implemented in C. If I useceil(3/2), it works fine. But when I useceil(count/2), if value of count is 3, then it gives compile time error./tmp/ccA4Yj7p.o(.text+0x364): In function
FrontBackSplit': : undefined reference toceil' collect2: ld returned 1 exit statusHow to use the ceil function in second case? Please suggest.
How can I implement my own ceil function in C. Please give some basic guidelines.
该
ceil()函数是用 C 实现的。如果我使用ceil(3/2)，它工作正常。但是当我使用时ceil(count/2)，如果 count 的值为 3，那么它会给出编译时错误。/tmp/ccA4Yj7p.o(.text+0x364): 在函数
FrontBackSplit': : undefined reference toceil' collect2: ld 返回 1 退出状态如何在第二种情况下使用 ceil 函数？请建议。
我如何在 C 中实现我自己的 ceil 函数。请给出一些基本指南。
Thanks.
谢谢。
采纳答案by Adam Rosenfield
The ceil()function is implemented in the math library, libm.so. By default, the linker does not link against this library when invoked via the gcc frontend. To link against that library, pass -lmon the command line to gcc:
该ceil()函数在数学库中实现，libm.so. 默认情况下，当通过 gcc 前端调用时，链接器不会链接到这个库。要链接到该库，-lm请将命令行传递给 gcc：
gcc main.c -lm
回答by nintendo
Try this out:
试试这个：
#define CEILING_POS(X) ((X-(int)(X)) > 0 ? (int)(X+1) : (int)(X))
#define CEILING_NEG(X) ((X-(int)(X)) < 0 ? (int)(X-1) : (int)(X))
#define CEILING(X) ( ((X) > 0) ? CEILING_POS(X) : CEILING_NEG(X) )
Check out the link for comments, proof and discussion: http://www.linuxquestions.org/questions/programming-9/ceiling-function-c-programming-637404/
查看评论、证明和讨论的链接：http: //www.linuxquestions.org/questions/programming-9/ceiling-function-c-programming-637404/
回答by Michael Aaron Safyan
The prototype of the ceilfunction is:
ceil函数的原型是：
double ceil(double)
My guess is that the type of your variable countis not of type double. To use ceil in C, you would write:
我的猜测是您的变量count类型不是 double 类型。要在 C 中使用 ceil，你可以这样写：
#include <math.h>
// ...
double count = 3.0;
double result = ceil(count/2.0);
In C++, you can use std::ceilfrom <cmath>; std::ceil is overloaded to support multiple types:
在 C++ 中，您可以使用std::ceilfrom <cmath>; std::ceil 被重载以支持多种类型：
#include <cmath>
// ...
double count = 3.0;
double result = std::ceil(count/2.0);
回答by Anonymous
double ceil (double x) {
if (x > LONG_MAX) return x; // big floats are all ints
return ((long)(x+(0.99999999999999997)));
}
