Add C++ example README.md and add more documentation.

GitOrigin-RevId: c75b98548766f5cabe02dc8eeb63049bd0847e8c

README.md

@@ -81,9 +81,9 @@ cmake -DCMAKE_BUILD_TYPE=Release -DOPENSSL_ROOT_DIR=/usr/local/opt/openssl/ ..
 C:\src\vcpkg> .\vcpkg install openssl zlib
 ```
 * Build `TDLib` with CMake as explained in [building](#building), but instead of `cmake -DCMAKE_BUILD_TYPE=Release ..` use
-  ```
-  cmake -DCMAKE_TOOLCHAIN_FILE=C:\src\vcpkg\scripts\buildsystems\vcpkg.cmake ..
-  ```
+```
+cmake -DCMAKE_TOOLCHAIN_FILE=C:\src\vcpkg\scripts\buildsystems\vcpkg.cmake ..
+```
 
 <a name="linux"></a>
 #### Linux

example/cpp/README.md

@@ -0,0 +1,20 @@
+# TDLib cpp basic usage examples
+
+TDLib should be prebuilt and installed to local subdirectory `td/`:
+```
+cd <path to TDLib sources>
+mkdir build
+cd build
+cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX:PATH=../example/cpp/td ..
+cmake --build . --target install
+```
+Also see [building](https://github.com/tdlib/td#building) for additional details on TDLib building.
+
+Then you can build the examples:
+```
+cd <path to TDLib sources>/example/cpp
+mkdir build
+cd build
+cmake -DCMAKE_BUILD_TYPE=Release -DTd_DIR=<full path to TDLib sources>/example/cpp/td/lib/cmake/Td ..
+cmake --build .
+```

example/cpp/td_example.cpp

@@ -20,6 +20,7 @@
 
 // Simple single-threaded example of TDLib usage.
 // Real world programs should use separate thread for the user input.
+// Example includes user authentication, receiving updates, getting chat list and sending text messages.
 
 // overloaded
 namespace detail {

example/cpp/tdjson_example.cpp

@@ -5,17 +5,29 @@
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 #include <iostream>
-#include <string>
 #include <td/telegram/td_json_client.h>
 
-int main(void) {
+// Basic example of TDLib JSON interface usage.
+// Native interface should be preferred instead in C++, so here is only an example of
+// the main event cycle, which should be essentially the same for all languages.
+
+int main() {
   void *client = td_json_client_create();
+  // somehow share the client with other threads, which will be able to send requests via td_json_client_send
+
+  const double WAIT_TIMEOUT = 10.0;  // seconds
   while (true) {
-    std::string str = td_json_client_receive(client, 10);
-    if (!str.empty()) {
-      std::cout << str << std::endl;
-      break;
+    const char *result = td_json_client_receive(client, WAIT_TIMEOUT);
+    if (result != nullptr) {
+      // parse the result as JSON object and process it as an incoming update or an answer to a previously sent request
+
+      // if (result is UpdateAuthorizationState with authorizationStateClosed) {
+      //   break;
+      // }
+
+      std::cout << result << std::endl;
     }
   }
-  return 0;
+
+  td_json_client_destroy(client);
 }