Emscripten calling JS from C and returning by reference (pointer)
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 can be called using the following JS which modifies the contents of buffer:
<!DOCTYPE html>
<html>
<body>
<script>
function js_receive(a,b,c,d) {
var bstr = Pointer_stringify(b);
document.write(a + " " + bstr + " " + c + " " + d);
setValue(b , 84, 'i8');
setValue(b+1, 87, 'i8');
setValue(b+2, 79, 'i8');
setValue(b+3, 0, 'i8');
return 42;
}
</script>
<script src="calljs.js"></script>
</body>
</html>
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