[ale] Missing "floor"?

[Ed Cashin]

Yes, ignoring stuff like inline functions defined in headers, standard
UNIX-like expectations would be for the header math.h to contain a function
*prototype* that *declares* floor.

The library contains the compiled floor function *definition* as executable
code for your architecture.  The source for the definition is part of
glibc, probably a function body *defined* in a .c file.

Both the source and the compiled form of the function can be thought of as
the implementation in different forms.  The declaration in the header is
information that the compiler can use to make sure that the types of the
function parameters and of the return value are right.  You can think of
the header stuff as "interface" as opposed to "implementation", but the C
language and runtime aren't essentially modular, so you'll exhaust the
usefulness of that metaphor if you go very deep.

Usually the specific difference is the compiler option Sparr mentions.  You
can see that on the CentOS 6 system I'm using, the option isn't required:

[ecashin at marino ~]$ cat > t.c
#include <math.h>
#include <stdio.h>

int main(void)
{
        printf("%g\n", floor(2.3));
        return 0;
}
[ecashin at marino ~]$ gcc -Wall t.c
[ecashin at marino ~]$ ./a.out
2
[ecashin at marino ~]$ gcc -Wall t.c -lm
[ecashin at marino ~]$ ./a.out
2
[ecashin at marino ~]$


On Wed, Jun 19, 2013 at 10:54 AM, Sparr <sparr0 at gmail.com> wrote:

> math.h only declares the function. The implementation is in /var/lib/libm
> (math lib). You need to tell the compiler to link to that with -lm
> On Jun 19, 2013 10:52 AM, "leam hall" <leamhall at gmail.com> wrote:
>
>> Morning Ed!
>>
>> I'm looking around (googling) to understand what you mean and I'm not
>> getting it. math.h is included in the program and exists in /usr/include.
>>
>> Leam
>>
>>
>>
>> On Wed, Jun 19, 2013 at 10:30 AM, Ed Cashin <ecashin at noserose.net> wrote:
>>
>>> Maybe link the math library?  A quick check suggests that's it.
>>>
>>> [ecashin at marino ~]$ man floor | grep Link
>>>        Link with -lm.
>>> [ecashin at marino ~]$
>>>
>>>  On Wed, Jun 19, 2013 at 10:18 AM, leam hall <leamhall at gmail.com> wrote:
>>>
>>>>  Not sure why I'm getting:
>>>>
>>>> gcc -Wall -Werror -o rand rand.c
>>>> /tmp/ccAJ7e8S.o: In function `main':
>>>> rand.c:(.text+0x16): undefined reference to `floor'
>>>> collect2: ld returned 1 exit status
>>>>
>>>> ###
>>>> rand.c
>>>> ###
>>>>
>>>> #include <stdio.h>
>>>> #include <unistd.h>
>>>> #include <stdlib.h>
>>>> #include <math.h>
>>>>
>>>> int main(void) {
>>>>
>>>>     int num;
>>>>     float val = 2.3;
>>>>     num = floor(val);
>>>>     printf("num is %d.\n", num);
>>>>
>>>>     return 0;
>>>> }
>>>>
>>>> --
>>>> Mind on a Mission <http://leamhall.blogspot.com/>
>>>>
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>>>>
>>>
>>
>> --
>> Mind on a Mission <http://leamhall.blogspot.com/>
>>
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-- 
  Ed Cashin <ecashin at noserose.net>
  http://noserose.net/e/
  http://www.coraid.com/
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