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

.github/workflows/windows.yml

@@ -12,6 +12,11 @@ jobs:
         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
@@ -27,7 +32,7 @@ jobs:
       shell: bash
       working-directory: ${{runner.workspace}}/build
       run: |
-        cmake -DCMAKE_BUILD_TYPE=${{matrix.build_type}} \
+        cmake -DCMAKE_BUILD_TYPE=${{matrix.build_type}} ${{matrix.shared}} \
               -A ${{matrix.platform}} $GITHUB_WORKSPACE
 
     - name: Build

include/fmt/format.h

@@ -37,9 +37,9 @@
 #include <cmath>
 #include <cstdint>
 #include <limits>
+#include <memory>
 #include <stdexcept>
 #include <utility>  // std::swap
-#include <memory>
 
 #include "core.h"
 
@@ -1295,7 +1295,7 @@ 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