From 7fda06adb818e8458aa42e1a35000a59b71ed107 Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Mon, 26 Apr 2021 09:33:36 +0200
Subject: [PATCH] Fix building for UHD 4.0.0.0

---
 CMakeLists.txt    | 10 ++++++----
 docs/changelog.md |  1 +
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 48d224584..0d846cdfb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -620,10 +620,12 @@ if(NOT (GNURADIO_VERSION VERSION_LESS 3.8) AND LOG4CPP_READY_FOR_CXX17)
             )
         endif()
         if(FILESYSTEM_FOUND)
-            if(CMAKE_VERSION VERSION_LESS 3.13)
-                set(CMAKE_CXX_STANDARD 17)
-            else()
-                set(CMAKE_CXX_STANDARD 20)
+            set(CMAKE_CXX_STANDARD 17)
+            if(CMAKE_VERSION VERSION_GREATER 3.13)
+                # UHD 4.0.0.0 still does not support C++20
+                if((NOT UHD_FOUND) OR (UHD_FOUND AND ("${UHD_VERSION}" VERSION_LESS 3.99)))
+                    set(CMAKE_CXX_STANDARD 20)
+                endif()
             endif()
             set(CMAKE_CXX_STANDARD_REQUIRED ON)
         endif()
diff --git a/docs/changelog.md b/docs/changelog.md
index 8d490a43a..d4f8dbd4c 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -92,6 +92,7 @@ SPDX-FileCopyrightText: 2011-2021 Carles Fernandez-Prades <carles.fernandez@cttc
 - Fix bug in searching for gr-iio when CMake was re-run several times with
   different settings for the `-DENABLE_FMCOMMS2` or `-DENABLE_PLUTOSDR` building
   options.
+- Fix building when using UHD v4.0.0.0.
 
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