[Vegter]

Hi

I'm unsure how to use functions that are declared as extern... I assume these are built-in functions in C that I can simply reference? But how do I do that?

Say, for example I want to use the built-in incomplete gamma function, that is

extern double igamc (double a, double x);

But I simply get a undefined reference compilation error: "Undefined reference to 'igamc'"
I've seen people use these functions, there are a whole list of them.

Thanks in advance

[Amadeus]

extern is a keyword the indicates the function (or variables) may be compiled as part of a separate module...have you included the correct libraries, or at least defined the function yourself?

[Vegter]

Ok, so the example program I was looking at was using the Cephes Maths library (I didn't realize it at the time and I thought it was built in). Anyone know how to correctly link the Cephes library into your program? The library can be found here.

[Amadeus]

You'll have to download it and install the libraries on your development machine...it comes with an installation guide, I believe...at the very least, there should be makefiles.

[Vegter]

Quote

You'll have to download it and install the libraries on your development machine...it comes with an installation guide, I believe...at the very least, there should be makefiles.

Thank you for the reply. I did download it, and it does come with an installation guide. Problem is, the whole package is 5 meg, and I only want to use 4 functions in total. So obvioustly I don't want to include the whole package in my project. That means if I look under the 'double' directory (because that's the precision I want), and I would like to use the igam.c file. But I can't seem to figure out exactly what other files and functions I need to link to get it working... I get a few 'function not found' and a few 'conflicting types' declarations when I try and compile the file. Maybe someone here has used this library (because it looks really well-written and very useful).

So here's what I did...
I copied the igam.c file from the 'double' directory to a new directory. I copied the 'mconf.h' file from the home directory to this new directory. The installation guide (which is only like 15 lines btw) says every subdirectory contains a file called 'protos.h' which I will need). But the 'double' subdirectory doesn't contain such a file! If I compile the igam.c file without it, I get a lot of errors. So I include the "mconf.h" file and <math.h> and compile it using

gcc igam.c -lm -o Test

and then I get
'undefined reference to lgam'
'undefined reference to MAXLOG'
'undefined reference to mtherr'
'undefined reference to MACHEP'

If someone can help me with this, I will be forever grateful.

[hwadhar]

Did you ever resolve this? I am having the same issue.

[no2pencil]

Can you post all of your code? Or at least everything prior to main