quick C question

[Scootin159]

I'm trying to use PI, cos & sin in C (linux gcc compiler). I included <math.h>, but cannot figure out how to use PI, ect.

Also, do you guys know where (under a typical redhat instalation) I would find the math.h file so I can just read it & see what is in there?

 

[notfred]

RedHat 7.2

find / -name math.h

/usr/include/math.h
/usr/lib/bcc/include/math.h

 

[Scootin159]

<< RedHat 7.2

find / -name math.h

/usr/include/math.h
/usr/lib/bcc/include/math.h >>



When all else fails go for the blatantly obvious (/usr/include). Thanks notfred. I also know how to do a search now - very helpful.

 

[BlackOmen]

Hmm, someone correct me if I'm wrong, but the include file does not include a constant PI. I was taught to do const double PI=4*atan(1.0);.

 

[Scootin159]

Found this in the math.h file:

# define M_# define M_PI 3.14159265358979323846 /* pi */

 

[Scootin159]

still can't find how to do cos, should be y = cos(x); right?

/* Cosine of X. */
#define cos(Val) __TGMATH_UNARY_REAL_IMAG (Val, cos, ccos)

(from tgmath.h) <- which I included as well.

 

[BlackOmen]

I stand corrected on PI. As for cosine, it should be just y=cos(x); where x is in radians.

 

[Scootin159]

It seems it should be that way, but:

float theta = 0;
//convert theta to radians
theta *= (float)(M_PI/180);
c = cos(5);


gives me this:

gcc 1.c
/tmp/ccyHH7o0.o: In function `main':
/tmp/ccyHH7o0.o(.text+0x16c): undefined reference to `cos'
collect2: ld returned 1 exit status

 

[BlackOmen]

Works fine for me using gcc 2.95.3. You're absolutely sure you remember to include math.h?

Otherwise I would attribute it to the old version of gcc.

 

[Cerebus451]

You need to include -lm at the end of your compile line to include the math library in the link. The math library is not included by default on links.

 

[Scootin159]

<< You need to include -lm at the end of your compile line to include the math library in the link. The math library is not included by default on links. >>



That was it. Thanks guys.