ABS包括math.h中后'隐式声明...“错误 [英] abs 'implicit declaration...' error after including math.h

问题描述

我用 ABS（）功能，我加入的#include＆LT;文件math.h＆GT; 上方的code。不过，我不断收到此错误：

I used the abs() function and I added #include <math.h> at the top of code. But I keep getting this error:

hello.c:20:11: warning: implicit declaration of function 'abs' is invalid in C99
[-Wimplicit-function-declaration]
      int a = abs(arrOfHour[i] - hour) * 60 + minute;
              ^

我使用LLVM编译器。

I'm using LLVM compiler.

为什么即使我已经包含发生此错误文件math.h ？

Why does this error occurs even though I have included math.h?

推荐答案

我要在文档直引号：的\"Prototypes于ABS，实验室和llabs在stdlib.h中

I'm going to quote straight from the docs : "Prototypes for abs, labs and llabs are in stdlib.h"

作为一个经验法则，关于浮点数操作的数学函数是在math.h中，并且对整数操作的是stdlib.h中

As a rule of thumb the mathematical functions that operate on floating point numbers are in math.h, and the ones that operate on integers are in stdlib.h.

有一个 pretty良好的维基百科文章基于C数学函数，如果您需要了解更多信息。

There's a pretty good Wikipedia article on C mathematical functions if you need more information.

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