Added comments about checking return code and the maxfd counter

docs/examples/10-at-a-time.c

@@ -123,6 +123,9 @@ int main(void)
         return EXIT_FAILURE;
       }
 
+      /* In a real-world program you OF COURSE check the return that maxfd is
+         bigger than -1 so that the call to select() below makes sense! */
+
       if (curl_multi_timeout(cm, &L)) {
         fprintf(stderr, "E: curl_multi_timeout\n");
         return EXIT_FAILURE;

docs/examples/fopen.c

@@ -153,6 +153,10 @@ fill_buffer(URL_FILE *file,int want,int waittime)
         /* get file descriptors from the transfers */
         curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
 
+        /* In a real-world program you OF COURSE check the return code of the
+           function calls, *and* you make sure that maxfd is bigger than -1
+           so that the call to select() below makes sense! */
+
         rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
         switch(rc) {

docs/examples/multi-app.c

@@ -80,6 +80,10 @@ int main(int argc, char **argv)
     /* get file descriptors from the transfers */
     curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
 
+    /* In a real-world program you OF COURSE check the return code of the
+       function calls, *and* you make sure that maxfd is bigger than -1 so
+       that the call to select() below makes sense! */
+
     rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
     switch(rc) {

docs/examples/multi-debugcallback.c

@@ -153,6 +153,10 @@ int main(int argc, char **argv)
     /* get file descriptors from the transfers */
     curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
 
+    /* In a real-world program you OF COURSE check the return code of the
+       function calls, *and* you make sure that maxfd is bigger than -1
+       so that the call to select() below makes sense! */
+
     rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
     switch(rc) {

docs/examples/multi-double.c

@@ -71,6 +71,10 @@ int main(int argc, char **argv)
     /* get file descriptors from the transfers */
     curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
 
+    /* In a real-world program you OF COURSE check the return code of the
+       function calls, *and* you make sure that maxfd is bigger than -1 so
+       that the call to select() below makes sense! */
+
     rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
     switch(rc) {

docs/examples/multi-post.c

@@ -93,6 +93,10 @@ int main(int argc, char *argv[])
       /* get file descriptors from the transfers */
       curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
 
+      /* In a real-world program you OF COURSE check the return code of the
+         function calls, *and* you make sure that maxfd is bigger than -1
+         so that the call to select() below makes sense! */
+
       rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
       switch(rc) {

docs/examples/multi-single.c

@@ -65,6 +65,10 @@ int main(int argc, char **argv)
     /* get file descriptors from the transfers */
     curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
 
+    /* In a real-world program you OF COURSE check the return code of the
+       function calls, *and* you make sure that maxfd is bigger than -1 so
+       that the call to select() below makes sense! */
+
     rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
 
     switch(rc) {