Fix linkage errors when linking with a shared library (#2011)

.github/workflows/windows.yml

@@ -0,0 +1,44 @@
+name: windows
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ${{matrix.os}}
+    strategy:
+      matrix:
+        # windows-2016 and windows-2019 have MSVC 2017 and 2019 installed
+        # respectively: https://github.com/actions/virtual-environments.
+        os: [windows-2016, windows-2019]
+        platform: [Win32, x64]
+        build_type: [Debug, Release]
+        include:
+          - os: windows-2016
+            platform: Win32
+            build_type: Debug
+            shared: -DBUILD_SHARED_LIBS=ON
+        exclude:
+          - os: windows-2016
+            platform: Win32
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Create Build Environment
+      run: cmake -E make_directory ${{runner.workspace}}/build
+
+    - name: Configure
+      # Use a bash shell for $GITHUB_WORKSPACE.
+      shell: bash
+      working-directory: ${{runner.workspace}}/build
+      run: |
+        cmake -DCMAKE_BUILD_TYPE=${{matrix.build_type}} ${{matrix.shared}} \
+              -A ${{matrix.platform}} $GITHUB_WORKSPACE
+
+    - name: Build
+      working-directory: ${{runner.workspace}}/build
+      run: cmake --build . --config ${{matrix.build_type}}
+
+    - name: Test
+      working-directory: ${{runner.workspace}}/build
+      run: ctest -C ${{matrix.build_type}}

include/fmt/format.h

@@ -1274,7 +1274,7 @@ template <typename T> struct decimal_fp {
   int exponent;
 };
 
-template <typename T> decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT;
+template <typename T> FMT_API decimal_fp<T> to_decimal(T x) FMT_NOEXCEPT;
 }  // namespace dragonbox
 
 template <typename T>

include/fmt/os.h

@@ -378,7 +378,7 @@ struct ostream_params {
 static constexpr detail::buffer_size buffer_size;
 
 // A fast output stream which is not thread-safe.
-class ostream final : private detail::buffer<char> {
+class FMT_API ostream final : private detail::buffer<char> {
  private:
   file file_;
 

src/format.cc

@@ -24,9 +24,9 @@ int format_float(char* buf, std::size_t size, const char* format, int precision,
                        : snprintf_ptr(buf, size, format, precision, value);
 }
 
-template dragonbox::decimal_fp<float> dragonbox::to_decimal(float x)
+template FMT_API dragonbox::decimal_fp<float> dragonbox::to_decimal(float x)
     FMT_NOEXCEPT;
-template dragonbox::decimal_fp<double> dragonbox::to_decimal(double x)
+template FMT_API dragonbox::decimal_fp<double> dragonbox::to_decimal(double x)
     FMT_NOEXCEPT;
 
 // DEPRECATED! This function exists for ABI compatibility.

src/os.cc

@@ -315,7 +315,7 @@ long getpagesize() {
 #  endif
 }
 
-void ostream::grow(size_t) {
+FMT_API void ostream::grow(size_t) {
   if (this->size() == this->capacity()) flush();
 }
 #endif  // FMT_USE_FCNTL