{"id":1800,"date":"2014-12-25T14:54:24","date_gmt":"2014-12-25T14:54:24","guid":{"rendered":"http:\/\/41j.com\/blog\/?p=1800"},"modified":"2014-12-23T14:57:33","modified_gmt":"2014-12-23T14:57:33","slug":"emscripten-calling-js-c-returning-reference-pointer","status":"publish","type":"post","link":"https:\/\/41j.com\/blog\/2014\/12\/emscripten-calling-js-c-returning-reference-pointer\/","title":{"rendered":"Emscripten calling JS from C and returning by reference (pointer)"},"content":{"rendered":"

JS code can manipuate memory directly using setValue, here’s a quick example of returning by reference. The C code is as follows:<\/p>\n

\r\n#include <stdio.h>\r\n#include <emscripten.h>\r\n#include <string.h>\r\n\r\nint main() {\r\n\r\n  char buffer[10];\r\n  strcpy(buffer,"nothing");\r\n\r\n  int ret = EM_ASM_INT({\r\n    return js_receive($0,$1,$2,$3);\r\n  }, 1,buffer,3,4);\r\n\r\n  printf("returned: %d\\n",ret);\r\n  printf("buffer  : %s\\n",buffer);\r\n\r\n  char call[100];\r\n  strcpy(call,"alert('");\r\n  strcat(call,buffer);\r\n  strcat(call,"')");\r\n  emscripten_run_script(call);\r\n}\r\n<\/pre>\n
And can be called using the following JS which modifies the contents of buffer:<\/p>\n
\r\n <!DOCTYPE html>\r\n<html>\r\n<body>\r\n\r\n<script>\r\n\r\nfunction js_receive(a,b,c,d) {\r\n\r\n\r\n  var bstr = Pointer_stringify(b);\r\n  document.write(a + " " + bstr + " " + c + " " + d);\r\n\r\n  setValue(b  ,  84, 'i8');\r\n  setValue(b+1,  87, 'i8');\r\n  setValue(b+2,  79, 'i8');\r\n  setValue(b+3,   0, 'i8');\r\n\r\n  return 42;\r\n}\r\n\r\n<\/script>\r\n\r\n<script src="calljs.js"><\/script>\r\n\r\n\r\n<\/body>\r\n<\/html>\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
JS code can manipuate memory directly using setValue, here’s a quick example of returning by reference. The C code is as follows: #include <stdio.h> #include <emscripten.h> #include <string.h> int main() { char buffer[10]; strcpy(buffer,"nothing"); int ret = EM_ASM_INT({ return js_receive($0,$1,$2,$3); }, 1,buffer,3,4); printf("returned: %d\\n",ret); printf("buffer : %s\\n",buffer); char call[100]; strcpy(call,"alert(‘"); strcat(call,buffer); strcat(call,"’)"); emscripten_run_script(call); } And […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1],"tags":[],"class_list":["post-1800","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1RRoU-t2","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/1800","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/comments?post=1800"}],"version-history":[{"count":2,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/1800\/revisions"}],"predecessor-version":[{"id":1802,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/posts\/1800\/revisions\/1802"}],"wp:attachment":[{"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/media?parent=1800"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/categories?post=1800"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/41j.com\/blog\/wp-json\/wp\/v2\/tags?post=1800"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}