GNU Fortran - Function 'dcosd' has no IMPLICIT type

Question

I'm a newbie in Fortran coding also in GNU Fortran and Code::Blocks.

I've installed codeblocks-20.03mingw-setup on Win10 and now trying to run this piece of code from scratch:

program hello

implicit none

  real :: x = 0.0
  x = dcosd(x)

  write(*,*) x

end program

But in some reason I'm getting this Build message:

C:\...\Hello_Test\main.f90|7|Error: Function 'dcosd'  has no IMPLICIT type|

If I delete the line implicit none I get this message instead:

C:\...\Hello_Test\main.f90|5|undefined reference to `dcosd_'|

I'm pretty sure DCOSD is kind a standard functoun in gFortran. I tried some some solutions for "IMPLICIT type" problem, but with no result. I think the solution shuld be pretty obvious for experienced people but it eludes me.

Answer 1

First to clarify, dcosd() is not a standard intrinsic function in Fortran. It used to be available as an extension to the standard by some compilers. Fortran 2023 brings the generic version cosd() as a standard intrinsic function, but modern Fortran standards do not really work too much with the specific functions like dcosd() and it has not been made standard.

---

GCC version 7 is quite old. dcosd() is recognized in your code by versions 10 and later (I tested 10, 11, 12 and 13). For versions 7-9 you need the option -fdec-math, mentioned by francescalus in the first comment, to enable the non-standard extension.

However, with these later versions or with the -fdec-math option you will get another error

    6 |   x = dcosd(x)
      |            1
Error: ‘x’ argument of ‘dcosd’ intrinsic at (1) must be double precision

That will be fixed by double precision :: x = 0.

Or you can change dcosd() to the generic cosd(). In that case the single precision version will be used and the code will compile with either real or double precision in GCC version 10 and later.