Implement ceil function in C

Question

I have two questions regarding the ceil() function.

• The ceil() function is implemented in C. If I use ceil(3/2) , it works fine. But when I use ceil(count/2) , if count is 3, it gives a compile-time error.

  /tmp/ccA4Yj7p.o(.text + 0x364): In the FrontBackSplit': : undefined reference to function FrontBackSplit': : undefined reference to ceil' collect2: ld returned 1 exit status

  How to use ceil function in the second case? Please suggest.

• How can I implement my own ceil function in C. Please provide some basic recommendations.

Thanks.

Answer 1

The ceil() function is implemented in the libm.so math library. By default, the linker does not contact this library when called through the gcc interface. To link this library, pass -lm to the gcc command line:

 gcc main.c -lm 

Answer 2

Try the following:

 #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 to comments, evidence, and discussion: http://www.linuxquestions.org/questions/programming-9/ceiling-function-c-programming-637404/

Answer 3

The prototype function of ceil is:

 double ceil(double) 

I assume that the type of the variable count not of type double. To use ceil in C, you must write:

 #include <math.h> // ... double count = 3.0; double result = ceil(count/2.0); 

In C ++ you can use std::ceil from <cmath> ;; std :: ceil is overloaded to support several types:

 #include <cmath> // ... double count = 3.0; double result = std::ceil(count/2.0); 

Answer 4

 double ceil (double x) { if (x > LONG_MAX) return x; // big floats are all ints return ((long)(x+(0.99999999999999997))); }