display std::cout in app - c++

Question

I have quite a lot of debugging monitoring all over my program so whenever something undesired happens a message appears in XCode with "std::cout" showing what happended, where it happened, and so on.
While I was testing the app on an iPhone or iPad connected to my computer, this worked as well (as I always had XCode open to show the fault).
But now I installed the app on devices of several beta-testers and they do not see these messages...
Rewriting the code to route all the "cout" to a string would cost a lot of time as they appear everywhere in several classes and sub classes, etc...
is there a possibility of simply reading out the last line of the output console or detecting the event of writing to the console and then copying it over to a separate string?

Answer 1

This is something I've done on some android projects to forward stdout and stderr to logcat. You could use this same approach to forwards the stdout/stderr to anywhere you want:
struct stream {
const char *name;
int fd[2];
FILE *src;
};
static void*
log_thread(void *arg)
{
struct stream *stream = arg;
char buf[4000], *off = buf, *nl; // Can't be too big or android stops logging
for (ssize_t r = 0;;off += r, r = 0) {
if (off - buf < sizeof(buf) - 1) {
errno = 0;
r = read(stream->fd[0], off, (sizeof(buf) - 1) - (off - buf));
if (r <= 0) { if (errno == EINTR) continue; else break; }
off[r] = 0;
}
if ((nl = strrchr(off, '\n'))) {
*nl = 0; ++nl;
__android_log_write(ANDROID_LOG_INFO, stream->name, buf);
r = (off + r) - nl;
memcpy((off = buf), nl, r);
} else if (off - buf >= sizeof(buf)) {
__android_log_write(ANDROID_LOG_INFO, stream->name, buf);
r = 0; off = buf;
}
}
close(stream->fd[0]);
close(stream->fd[1]);
return NULL;
}
__attribute__((constructor)) static void
log_init(void) {
static struct stream stream[] = { { .name = "stdout" }, { .name = "stderr" } };
stream[0].src = stdout; stream[1].src = stderr;
for (size_t i = 0; i < sizeof(stream) / sizeof(stream[0]); ++i) {
setvbuf(stream[i].src, NULL, _IOLBF, BUFSIZ);
pipe(stream[i].fd);
dup2(stream[i].fd[1], fileno(stream[i].src));
pthread_t thread;
pthread_create(&thread, 0, log_thread, &stream[i]);
pthread_detach(thread);
}
}