Embedded Ruby Question

Ruby
1

Hi all,

I want to embed Ruby in my C++ application. I’d like to read one or
more
Ruby scripts stored in my RDBMS, pass the Ruby script as a string (not a
file name) to the interpreter, and have it execute the code. Is this
possible? If so, is there a URL that describes how to do this or shows
an
example?

Thanks!

-Brian

2

There’s a good section on embedding Ruby in the Pickaxe 2. You have to
be extremely careful with some aspects of it, especially if you use
threads (the Ruby interpreter is not currently thread safe).

3

Hi Timothy,

Thanks for the reply!

Yes, I have the Pickaxe 2. Unfortunately, it doesn’t describe/document,
what I need to do. It describes how to embed the interpreter,
call/execute
Ruby from an existing file, extend Ruby via C/C++, but it does not
describe
how to pass a string that is Ruby code from C++ to the interpreter and
have
it execute. That’s what I need.

Thanks.

-Brian

Brian E Campbell
[email protected]

4

As a matter of fact, ruby’s interpreter accepts the switch ‘-e’ to
execute any string following it as ruby source code.

for instance, when you entered as following,
ruby -e “puts 5”
the console would output 5.

you may execute such shell command in C/C++.
may it be of help.

5

As a matter of fact, ruby’s interpreter accepts the switch ‘-e’ to
execute any string following it as ruby source code.

for instance, when you entered as following,
ruby -e “puts 5”
the console would output 5.

you may execute such shell command in C/C++.
may it be of help.

6

Logan,

Excellent! This is exactly what I’m after. Thanks!

-Brian

Brian E Campbell
[email protected]

7

On Aug 1, 2006, at 9:28 PM, Brian Campbell wrote:

Thanks.

One of the best sources of documentation for C extensions is
README.EXT in the source distribution. Here is the relevant section
for what you want to do:

2.2.1 Evaluate Ruby P.s in a String

The easiest way to use Ruby’s functionality from a C program is to
evaluate the string as Ruby program. This function will do the job.

VALUE rb_eval_string(const char *str)

Evaluation is done under the current context, thus current local
variables
of the innermost method (which is defined by Ruby) can be accessed.

8

Hi,

At Wed, 2 Aug 2006 12:55:46 +0900,
Logan C. wrote in [ruby-talk:205673]:

VALUE rb_eval_string(const char *str)

It’s not exception safe. Use rb_eval_string_protect() for
embedded use.

9

Brian Campbell wrote:

I want to embed Ruby in my C++ application.

Here is some sample code I’d come up with (for 1.8.2, I think). You
may need to tweak it a bit.

– Timothy

// r_in_c.cpp : Sample program for embedding Ruby in C.
//

//#include “stdafx.h”
#include <tchar.h>
#include “stdio.h”
#include

#pragma warning(disable: 4312)

#include “ruby.h”
//#include “st.h”

void print_ruby_value(int v, int indent, const char* str)
{
VALUE val = (VALUE)(v);
int type = TYPE(v);
#if 1
switch (type) {
case T_FIXNUM:
printf("%*s%s ==> fixnum, value = %d\n", indent, “”, str,
FIX2INT(v));
break;
case T_NIL:
printf("%*s%s ==> nil\n", indent, “”, str);
break;
case T_FALSE:
printf("%*s%s ==> false\n", indent, “”, str);
break;
case T_TRUE:
printf("%*s%s ==> true\n", indent, “”, str);
break;
case T_UNDEF:
printf("%*s%s ==> undef\n", indent, “”, str);
break;
case T_SYMBOL:
printf("%*s%s ==> symbol (%d)\n", indent, “”, str,
SYM2ID(v));
break;
case T_STRING:
printf("%*s%s ==> string %*s\n", indent, “”, str,
RSTRING(v)->len, RSTRING(v)->ptr);
break;
case T_FLOAT:
printf("%*s%s ==> float %f\n", indent, “”, str,
RFLOAT(v)->value);
break;
case T_BIGNUM:
{
VALUE s = rb_String(val);
printf("%*s%s ==> bignum %*s\n", indent, “”, str,
RSTRING(s)->len, RSTRING(s)->ptr);
}
break;
case T_REGEXP:
printf("%s%s ==> regexp %*s\n", indent, “”, str,
RREGEXP(v)->len, RREGEXP(v)->str);
break;
case T_ARRAY:
{
char buffer[20];
long len = RARRAY(v)->len;
VALUE ptr = RARRAY(v)->ptr;
printf("%s%s ==> array (%d):\n", indent, “”, str, len);
for (long i = 0; i < RARRAY(v)->len; ++i)
{
sprintf(buffer, “a[%d]”, i);
print_ruby_value(ptr[i], indent+4, “default value”);
}
}
break;
case T_HASH:
{
RHash h = RHASH(v);
printf("%*s%s ==> hash (iter_lev %d):\n", indent, “”, str,
h->iter_lev);
print_ruby_value(h->ifnone, indent+4, “not found value”);

    struct st_table *tbl = h->tbl;;
    printf("%*sbins = %d, entries = %d\n", indent+4, "",

tbl->num_bins, tbl->num_entries);
}
break;
default:
printf("%*s%s ==> class %d\n", indent, “”, str, type);
break;
}
#else
switch (type) {
case T_NIL:
printf("%*s%s ==> nil\n", indent, “”, str);
break;
case T_ARRAY:
val = rb_ary_join(val, rb_str_new2(", “));
printf(”%*s%s ==> type(%d) [%*s]\n", indent, “”, str, type,
RSTRING(val)->len, RSTRING(val)->ptr);
break;
case T_REGEXP:
val = rb_String(val);
printf("%*s%s ==> type(%d) /%*s/\n", indent, “”, str, type,
RSTRING(val)->len, RSTRING(val)->ptr);
break;
default:
val = rb_String(val);
printf("%*s%s ==> type(%d) %*s\n", indent, “”, str, type,
RSTRING(val)->len, RSTRING(val)->ptr);
}
#endif

if (indent == 0) {
    printf("\n");
}

}

// Returns output of command as a string
//
// see rb_f_backquote() in io.c
//
// needs to set exit code of command into rb_last_status
//
static VALUE m_backquote(VALUE self, VALUE commandVal)
{
VALUE arr = Qnil;
char* commandStr = StringValueCStr(commandVal);

if (commandStr) {

    printf("Executing backquote command on `%s`\n", commandStr);

    // This should be the captured output of the command.
    // I'll just reverse the string as the command value, here.
    //
    size_t len = strlen(commandStr);
    std::string ss(len, ' ');
    for (size_t i = 0, j = len - 1; i < len; ++i, --j) {
        ss[i] = commandStr[j];
    }

    arr = rb_str_new2(ss.c_str());
}
else {
    printf("Error: cannot execute object\n");
}

return arr;

}

// Executes cmd in a subshell, returning true (Qtrue) if the command
// was found and ran successfully, false (Qfalse) otherwise.
//
// passed in elements may be arrays - may want to flatten and then
// join with " "s between.
//
// See rb_f_system() in process.c
//
// needs to set exit code of command into rb_last_status
//
static VALUE m_system(int argc, VALUE *argv)
{
printf(“Called Kernel#system on:\n”);

for (int i = 0; i < argc; ++i) {
    VALUE s = rb_String(argv[i]);
    printf("   %2d. `%*s`\n", i, RSTRING(s)->len, RSTRING(s)->ptr);
}

return Qtrue;

}

// Might want to have separate functions for stdout and stderr, so they
// can be separated…
//
static VALUE m_write_stdout(VALUE self, VALUE input)
{
if (TYPE(input) == T_STRING) {
printf("We have captured (stdout): "%s"\n",
RSTRING(input)->len, RSTRING(input)->ptr);
// Return the number of bytes written
return
rb_fix_new(RSTRING(input)->lensizeof(RSTRING(input)->ptr[0]));
}
else {
printf(“Error: cannot write object to stdout\n”);
return Qnil;
}
}
static VALUE m_write_stderr(VALUE self, VALUE input)
{
// Need to use rb_string_value if it can contain embedded nuls.
char * got = StringValueCStr(input);
printf(“We have captured (stderr): “%s”\n”, got);
// Return the number of bytes written
return rb_fix_new(strlen(got)*sizeof(got[0]));
}

int _tmain(int argc, _TCHAR* argv[])
{
NtInitialize(&argc, &argv);

ruby_init();
ruby_script("embedded");

rb_define_global_function("`", RUBY_METHOD_FUNC(m_backquote), 1);
rb_define_global_function("system", RUBY_METHOD_FUNC(m_system),

-1);

rb_define_singleton_method(rb_stdout, "write",

RUBY_METHOD_FUNC(m_write_stdout), 1);
rb_define_singleton_method(rb_stderr, “write”,
RUBY_METHOD_FUNC(m_write_stderr), 1);

char* eval_strings[] = {
    "3",
    "nil",
    "true",
    "false",
    "5+6",
    "?c",
    ":fred",
    "'hello'",
    "\"hello\"",
    "'hello there'",
    "'123'*3",
    "3.8",
    "x = 123_456",
    "x * x",
    "\"#{x * x}\"",
    "111_111_111**2",
    "-111_111_111**3",
    "[1, 'two', 3.0]",
    "[[1,2,3],[4,5,6],[7,8,9]]",
    "/r[iou]se/",
       "`dir c:\\\\windows`",
    "h = { 'dog' => 'canine', 'cat' => 'feline', 'donkey' =>

‘asinine’ } ",
“h.length”,
“h[‘dog’]”,
"h[‘cow’] = ‘bovine’ ",
"h[12] = ‘dodecine’ ",
"h[‘cat’] = 99 ",
“h”,
“puts ‘this is a test’”,
“$stderr.puts ‘writing to stderr’”,
“system(‘TITLE’, ‘4NT/Ruby’)”,
“system(‘DELAY 3 & TITLE Changed window title from Ruby’)”,
“5”,
};

const int eval_strings_len = sizeof(eval_strings) /

sizeof(eval_strings[0]);

int status = 0;

for (int i = 0; i < eval_strings_len; ++i) {
    status = rb_eval_string(eval_strings[i]);
    print_ruby_value(status, 0, eval_strings[i]);
}

ruby_cleanup(0);

return 0;

}