returning long string from gd php function?

I've created a new function in the gd library and in php_gd to read and write comment blocks in the gif file (I have a Unisys license). The gd library for this reading and writing works fine, as proven by command-line gd utilities. The trouble I am having is reading a long (more than 2000 characters) comment out of a file and returning it to a PHP script. I'm not much of a C programmer, I just modify things by imitating other functions. Here is the function in ext/gd/gd.c /* im, comment */ /* {{{ proto int imagecomment(int im [, string c]) Add or delete the comment */ PHP_FUNCTION(imagecomment) { zval **IM, **C = NULL; gdImagePtr im; unsigned char *string = NULL; unsigned char *output = NULL; unsigned char *input = NULL; int argc; GDLS_FETCH(); argc = ARG_COUNT(ht); switch(argc) { case 1: if (zend_get_parameters_ex(1, &IM) == FAILURE) { WRONG_PARAM_COUNT; } break; case 2: if (zend_get_parameters_ex(2, &IM, &C) == FAILURE) { WRONG_PARAM_COUNT; } convert_to_string_ex(C); break; default: WRONG_PARAM_COUNT; } ZEND_FETCH_RESOURCE(im, gdImagePtr, IM, -1, "Image", GDG(le_gd)); php_error(E_WARNING, "Comment3: =%s=", im->comment); if (argc == 2) { string = ( unsigned char *) (*C)->value.str.val; gdImageComment( im, string ); } /* output = gdImageGetComment( im ); */ output = im->comment; php_error(E_WARNING, "Comment4: =%d=%s=", strlen(output), output); RETVAL_STRINGL(output, strlen(output), 1); } /* }}} */ I'm really kind of lost at the end. I'm not sure whether to call gdImageGetComment, or just use im->comment as coded above. And I don't know what is the best what to assign or pass around long strings. Comment3 does indeed show the comment line intact, the trouble is returning it effectively. Again, for comments less than 2000 characters or so, it works. Larger (up to 10,000) gives a garbled comment back to the script, presumably because enough memory wasn't allocated or something. Could someone maybe please describe the way this output should be defined, populated, and returned? Thanks.