Build programs as C++20

Use g++-13 for Actions workflows.

Author: jwakely

.github/workflows/check-build.yml

@@ -23,7 +23,7 @@ jobs:
         fetch-depth: 1
 
     - name: Compile binary programs
-      run: make pgms
+      run: make CXX=g++-13 pgms
 
     - name: Check for carriage returns
       run: |

.github/workflows/check-pr.yml

@@ -21,7 +21,7 @@ jobs:
         fetch-depth: 1
 
     - name: Compile binary programs
-      run: make pgms
+      run: make CXX=g++-13 pgms
 
     - name: Extract issue timestamps from published files
       run: |

.github/workflows/deploy.yml

@@ -51,7 +51,7 @@ jobs:
       run: make dates
 
     - name: Build programs
-      run: make pgms -j 4
+      run: make CXX=g++-13 pgms -j4
 
     - name: Generate HTML lists
       run: make lists

Makefile

@@ -1,6 +1,6 @@
 # The binaries that we want to build
 PGMS := bin/lists bin/section_data bin/toc_diff bin/list_issues bin/set_status
-CXXFLAGS := -std=c++17 -Wall -g -O2 -D_GLIBCXX_ASSERTIONS
+CXXFLAGS := -std=c++20 -Wall -g -O2 -D_GLIBCXX_ASSERTIONS
 
 # Running 'make debug' is equivalent to 'make DEBUG=1'
 ifeq "$(MAKECMDGOALS)" "debug"

bin/build_pgms.bat

@@ -1,7 +1,7 @@
 echo "Use -m32 switch to force 32-bit build"
-g++ %* -std=c++17 -DNDEBUG -O2 -o bin/lists.exe  src/date.cpp src/issues.cpp src/status.cpp src/sections.cpp src/mailing_info.cpp src/report_generator.cpp src/metadata.cpp src/lists.cpp
-g++ %* -std=c++17 -o bin/section_data.exe src/section_data.cpp
-g++ %* -std=c++17 -o bin/toc_diff.exe src/toc_diff.cpp
-g++ %* -std=c++17 -DNDEBUG -O2 -o bin/list_issues.exe src/date.cpp src/issues.cpp src/status.cpp src/sections.cpp src/metadata.cpp src/list_issues.cpp
-g++ %* -std=c++17 -DNDEBUG -O2 -o bin/set_status.exe  src/set_status.cpp src/status.cpp
+g++ %* -std=c++20 -DNDEBUG -O2 -o bin/lists.exe  src/date.cpp src/issues.cpp src/status.cpp src/sections.cpp src/mailing_info.cpp src/report_generator.cpp src/metadata.cpp src/lists.cpp
+g++ %* -std=c++20 -o bin/section_data.exe src/section_data.cpp
+g++ %* -std=c++20 -o bin/toc_diff.exe src/toc_diff.cpp
+g++ %* -std=c++20 -DNDEBUG -O2 -o bin/list_issues.exe src/date.cpp src/issues.cpp src/status.cpp src/sections.cpp src/metadata.cpp src/list_issues.cpp
+g++ %* -std=c++20 -DNDEBUG -O2 -o bin/set_status.exe  src/set_status.cpp src/status.cpp