c_link check if symbol loaded with dynamic link

## Syntax

    c_link(routine_name)
                [test, ilib] = c_link(routine_name)
                test = c_link(routine_name,num)

## Arguments

routine_name

  a character string

num

  number of the shared library where routine_name is searched (-1: default, last used)

test

  boolean, indicates if there is a shared library which contains `routine_name`.

ilib

  a scalar, the number of the shared library which contains `routine_name`

## Description

`c_link` is a boolean function which checks if the routine `routine_name` is currently linked. This function returns a boolean value true or false. When used with two return values, the function `c_link` returns a boolean value in `test` and the number of the shared library which contains `routine_name` in `ilib` (when `test` is true).

## Examples (C code)

    if haveacompiler() then
                chdir(TMPDIR)
                f1=['int ext1c(int *n, double *a, double *b, double *c)'
                '{int k;'
                '  for (k = 0; k < *n; ++k) '
                '      c[k] = a[k] + b[k];'
                '  return(0);}'];

                mputl(f1, TMPDIR + '/fun1.c');
                //creating the shared library (a gateway, a Makefile and a loader are
                //generated.
                ilib_for_link('ext1c','fun1.c',[],"c");
                // load the shared library
                exec loader.sce;
                // show link
                link('show')

                [test, ilib] = c_link('ext1c') // check if 'ext1c' symbol is linked in scilab (it returns %T, ilib equals to 0)
                c_link('ext1c', -1) // check if 'ext1c' linked in scilab in current library (last used) (it returns %T)
                c_link('ext1c', 0) // check in library (id eqs 0) if 'ext1c' is linked (it returns %T)
                c_link('ext1c', 1) // 'ext1c' not in library with id = 1 (it returns %F)
                c_link('toto') // returns %F  'toto' not linked to scilab (it returns %F)
                end

## See also

- link