What kind of assistance are you looking for? Are you looking for an explanation of the error message? Are you looking for help in how to fix the cause of the errors?
Below is a rough explanation of the error message. If you already knew all this, then I apologize. It's the only thing I could come up with given the vagueness of your request. (I say "rough" because I'm not 100% sure of a couple things, so I'm extrapolating based on things I'm sure of.)
Here's the error message:
Code:
Undefined symbols for architecture i386:
"_date_", referenced from:
_header_ in header.o
"_timer_", referenced from:
_MAIN__ in couple.o
ld: symbol(s) not found for architecture i386
collect2: error: ld returned 1 exit status
make: *** [couple] Error 1
This is telling you that there are functions, subroutines, or global data names that are not defined. That is, the program is referring to something outside the .f file, and that something isn't defined by any other .f file or library.
I can't tell you what the "something" is. It could be a function, subroutine, or global data name. All of those are termed "symbols", so that's what "Undefined symbols" means.
Here are the specifics:
The symbol date is used in the routine named header, which is in the "header.f" file.
The symbol timer is used in the routine named MAIN, which is in the "couple.f" file.
I'm giving the symbol name as I suspect it will appear in the Fortran source. It may also be uppercase, i.e. DATE instead of date. And MAIN may be a PROGRAM statement.
The actual symbol in the compiled object-file has a leading and trailing '_', which are automatically added by the Fortran compiler. The compiler does this so Fortran symbols are distinct from those in other compiled languages, such as C. To get the original symbol name, one must remove these additions.
The transformation from a Fortran symbol name into a compiled symbol-name is one of the things I'm unsure of. The C convention is to only prepend an '_', so the C function foo() ends up as the compiled symbol _foo. Other languages have other transformations, so I'm guessing that Fortran's is to both prepend and append an '_'.
I can't explain any more than this, because I can't tell if the Fortran code is expecting date and timer to be provided by a missing source file, or by a library. If it's expecting those to be in a library, then you'll have to explain where the source is from, so we can see what its dependencies are. If you wrote it entirely yourself, then you have to tell us what library it depends on.
As shown, the command that links the .o files isn't referring to any other libraries, which means that only the standard Fortran library (i.e. builtin functions & such) will be used. If the missing symbols are from another library, you have to tell the linker what that library is.
If the missing symbols are expected to be in the standard Fortran library, then please post the source from "header.f" and "couple.f" that shows the references to the symbol. The first step to understanding what the code is expecting is to see it in use.
As an example, if I google for
gfortran timer, I find the following:
https://gcc.gnu.org/onlinedocs/gfortran/CPU_005fTIME.html
https://gcc.gnu.org/onlinedocs/gfortran/TIME.html
https://gcc.gnu.org/onlinedocs/gfortran/SYSTEM_005fCLOCK.html
http://stackoverflow.com/questions/...ines-which-is-better-cpu-time-or-system-clock
http://people.sc.fsu.edu/~jburkardt/f_src/timer/timer.html
The first 3 references are the gfortran standard library routines CPU_TIME, TIME, and SYSTEM_CLOCK. None of these are the exact name
timer. However, if Fortran is using timer to measure elapsed time, it may allow you (or someone else) to make an equivalent using one of those routines.
The 4th and 5th links discuss timing of runs. If that's what your code is doing, they may be useful in applying the library routines.
