Where are the c header files on my system?

[Kevin D. Clark]

Lori Nagel writes:

> I've been using gcc in Linux and cc in Unix.  I have not been using
> an IDE, only the terminal shell and a text editing program for the C
> files. On both computers c programs compile and run, however, the
> compilers are different and have different options, and some code
> that compiles and runs on one doesn't on the other.  (what I mean is
> why is gcc so lax while cc is so mean.)

I strongly recommend that when you compile all of your C code with gcc
that you add the arguments "-Werror -Wall -Wcast-qual".

You can either do this or spend your time chasing crazy problems.
Your choice.

> What I want to know is if there any easy way I could find out where
> my .h files are on my computers such as stdio.h? Also, would I be
> able to find the function prototypes for things like scanf in them
> or would I have to go somewhere else?

If you want to know where to #include things from, the very first
place you should look is in the manual page.  If you type "man scanf"
you will see this:

   SYNOPSIS
       #include <stdio.h>
       int scanf(const char *format, ...);
       int fscanf(FILE *stream, const char *format, ...);
       int sscanf(const char *str, const char *format, ...);


The way that you should interpret this is "if I want to use the
scanf() function, I need to #include <stdio.h> in my code.


> Another thing, why oh why did they decide to seperate out libm.a
> from the rest of the C programming libriaries so that you have to
> include it? It used to make me so upset until I read intro to gcc.

Again, the problem that you are describing here is easily remedied if
you consult the manual page.  For example, "man atanf" produces:

   SYNOPSIS
       #include <math.h>

       double atan(double x);
       float atanf(float x);
       long double atanl( long double x);

       Link with -lm.


You should interpret this to mean (1) if you want to use the math
library, you need to #include <math.h> and (2) if you want to use the
math library, you need to link against it by adding the argument "-lm"
to your invocation of the linker, like so: "cc foo.o -o foo -lm".


> Please someone answer my question because I have been wanting to
> know the answer for about 3 years now, and I think that is a long
> enough time to wait.  I have done enough reading of manuals to know
> that most of them don't answer the questions that people have. I'm
> planning to write the ultimate newbie C programming book for
> Gnu/Linux because it doesn't currently exist.

The two best books that I know of on the C language are Kernighan and
Ritchie's book and Harbison and Steele's book.

Regards,

--kevin
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