如何使用Emscripten将对象从Javascript传递到C++
How do I pass objects from Javascript to C++ using Emscripten
我想把一个Javascript对象从JS传递回C++类/方法。我有以下不起作用的简单代码片段:
// Access JS objects in C++ like C++ objects
#include "emscripten/val.h" //Causing errors !
using namespace emscripten;
int main() {
val Math = val::global("Math");
return Math.call("abs", -10); // returns 10
}
我使用以下代码在windows上使用emscripten进行编译:
cmd>emcc Access_Objects.cpp
我得到大量错误日志:
In file included from Access_Objects.cpp:2:
In file included from C:Program FilesEmscriptenemscripten1.16.0systeminclu
deemscripten/val.h:4:
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:2
4:5: error:
unknown type name 'constexpr'
constexpr bool has_unbound_type_names = true;
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:2
4:15: error:
expected unqualified-id
constexpr bool has_unbound_type_names = true;
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:5
6:21: error:
use of undeclared identifier 'has_unbound_type_names'
if (has_unbound_type_names || std::is_polymorphic<C>::value) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:6
7:17: error:
use of undeclared identifier 'has_unbound_type_names'
if (has_unbound_type_names || std::is_polymorphic<C>::value) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:8
2:40: error:
a space is required between consecutive right angle brackets (use '> >')
struct TypeID<std::unique_ptr<T>> {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:9
8:42: error:
a space is required between consecutive right angle brackets (use '> >')
struct TypeID<AllowedRawPointer<T>> {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
82:9: error:
unknown type name 'constexpr'
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(char);
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:13: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
82:9: error:
expected member name or ';' after declaration specifiers
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(char);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:23: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
~~~~~~~~~ ^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
83:9: error:
unknown type name 'constexpr'
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(signed char);
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:13: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
83:9: error:
expected member name or ';' after declaration specifiers
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(signed char);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:23: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
~~~~~~~~~ ^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
84:9: error:
unknown type name 'constexpr'
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(unsigned char);
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:13: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
84:9: error:
expected member name or ';' after declaration specifiers
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(unsigned char);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:23: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
~~~~~~~~~ ^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
85:9: error:
unknown type name 'constexpr'
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(signed short);
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:13: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
85:9: error:
expected member name or ';' after declaration specifiers
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(signed short);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:23: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
~~~~~~~~~ ^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
86:9: error:
unknown type name 'constexpr'
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(unsigned short);
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:13: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
86:9: error:
expected member name or ';' after declaration specifiers
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(unsigned short);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:23: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
~~~~~~~~~ ^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
87:9: error:
unknown type name 'constexpr'
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(signed int);
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:13: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
87:9: error:
expected member name or ';' after declaration specifiers
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(signed int);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:23: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
~~~~~~~~~ ^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
88:9: error:
unknown type name 'constexpr'
EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE(unsigned int);
^
C:Program FilesEmscriptenemscripten1.16.0systemincludeemscripten/wire.h:1
74:13: note:
expanded from macro 'EMSCRIPTEN_DEFINE_NATIVE_BINDING_TYPE'
constexpr static WireType toWireType(const type& v) {
^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
ERROR root: compiler frontend failed to generate LLVM bitcode, halting
错误是由'emscripten/val.h'中包含的'wire.h'引起的。
如何解决这些错误?或有没有其他方法可以将对象从JS传递到C++?
JS和C++之间还有其他交互方式。我发现的最稳定的方法是通过包装JS函数来构建自己的库,这样您就可以从C++中调用它们。
如果你想从C++中调用Javascript的Math.abs((,你可以编辑"src/library.JS"。在那里你会发现C++中可用的函数名的巨大映射。如果您想将新函数称为"JS_Math_abs",您可以添加:
JS_Math_abs: function(value) {
return Math.abs(value);
},
然后,您将修改C++代码以指定输入和输出类型。添加:
extern "C" {
extern int JS_Math_abs(int);
}
不要误解我的意思,这种方法比val应该的更烦人(如果它工作正常的话(,但它最终也应该更高效。一旦您有了所需的主库,您就会发现它非常稳定。然而,在大多数情况下,使用像abs((这样的C++版本的函数是很容易的。
您可以在这里找到更多关于创建自己的库的信息:http://kripken.github.io/emscripten-site/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.html#interacting-使用来自本机的代码调用javascript
如上所述,您需要将-std=c++11传递给编译器,因为它使用c++11
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