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