GCC can't find some complex.h functions

With code like this:

Code:

---

#include <stdio.h>
#include <complex.h>
#include <math.h>


int main(int argc, char *argv[]) {


    double complex z1 = 0.0 + 1.0 * I;
    double a = csin(z1);
    printf("%lf", a);


    return 0;
}

---

I get - undefined reference to `csin' and several other complex functions
But some functions work eg creal and cimag but others do no.
This is with gcc compiler, through Netbeans, on Debian Mint.
The compiler standard is set to C99.
TIA

Link with the math library.

Code:

---


$ gcc foo.c
/tmp/ccm0ndwS.o: In function `main':
foo.c:(.text+0x3c): undefined reference to `csin'
collect2: error: ld returned 1 exit status
$ gcc foo.c -lm
$

---

Quote:

---

Originally Posted by man page

NAME
csin, csinf, csinl - complex sine function

SYNOPSIS
#include <complex.h>

double complex csin(double complex z);
float complex csinf(float complex z);
long double complex csinl(long double complex z);

Link with -lm.

---

OK thanks this works. Can you explain why this is needed? Is it because gcc treats these as 'built-in' functions?

And why it does not work from Netbeans, with command line options set to:
-m64 -lm -g -Wall -std=c99
?

> Can you explain why this is needed?
Because the manual says so.

Everything in the C standard library except math is resolved by libc, and that is linked by the compiler by default.
The math library is separate, because of history.


> -m64 -lm -g -Wall -std=c99?

Code:

---

$ gcc foo.c -lm
$ gcc -lm foo.c
/tmp/ccIluqrt.o: In function `main':
foo.c:(.text+0x3c): undefined reference to `csin'
collect2: error: ld returned 1 exit status

---

Some things are order dependent.

The linker needs to know that 'csin' is undefined as a result of compiling your code before it read the definition of 'csin' from the library.

But functions in math.h eg exp do not require the -lm flag (even though the manual says they do) - either in gcc at the command line or from Netbeans

Sometimes you need -lm, and other times you don't.

Code:

---

$ cat foo.c
#include <stdio.h>
#include <math.h>

int main(){
  double x = 10.0;
  double y = exp(x);
  printf("%lf = %lf\n", x, y);
  return 0;
}
$ gcc foo.c
/tmp/cceZwDmN.o: In function `main':
foo.c:(.text+0x23): undefined reference to `exp'
collect2: error: ld returned 1 exit status

$ gcc -O2 foo.c

---

Other Builtins (Using the GNU Compiler Collection (GCC))

Quote:

---

Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function is emitted.

---

So, depending on too many factors to possibly list, any given call to a math function may or may not necessitate the addition of the -lm linker option.