Fix fstream optimization

src/internal/cfileinstream.cpp

@@ -25,9 +25,18 @@ CFileInStream::CFileInStream( const fs::path& filePath ) : CStdInStream( mFileSt
     /* By default, file stream performance is relatively poor due to the default buffer size used
      * (e.g., GCC uses a small 1024-bytes buffer).
      * This is a known problem (see https://stackoverflow.com/questions/26095160/why-are-stdfstreams-so-slow).
-     * We make the underlying file stream use a bigger buffer (1 MiB) for optimizing the reading of big files.  */
+     * We make the underlying file stream use a bigger buffer (1 MiB) for optimizing the reading of big files.
+     * Note: when using libstdc++, the buffer must be set before opening the file. */
+
+#ifdef __GLIBCXX__
     mFileStream.rdbuf()->pubsetbuf( mBuffer.data(), kBufferSize );
+#endif
+
     openFile( filePath );
+
+#ifndef __GLIBCXX__
+    mFileStream.rdbuf()->pubsetbuf( mBuffer.data(), kBufferSize );
+#endif
 }
 
 void CFileInStream::openFile( const fs::path& filePath ) {

src/internal/cfileoutstream.cpp

@@ -32,7 +32,11 @@ CFileOutStream::CFileOutStream( fs::path filePath, bool createAlways )
         }
         throw BitException( "Failed to create the output file", error, path_to_tstring( mFilePath ) );
     }
+
+#ifdef __GLIBCXX__
     mFileStream.rdbuf()->pubsetbuf( mBuffer.data(), kBufferSize );
+#endif
+
     mFileStream.open( mFilePath, std::ios::binary | std::ios::trunc ); // flawfinder: ignore
     if ( mFileStream.fail() ) {
 #if defined( __MINGW32__ ) || defined( __MINGW64__ )
@@ -42,6 +46,10 @@ CFileOutStream::CFileOutStream( fs::path filePath, bool createAlways )
         throw BitException( "Failed to open the output file", last_error_code(), path_to_tstring( mFilePath ) );
 #endif
     }
+
+#ifndef __GLIBCXX__
+    mFileStream.rdbuf()->pubsetbuf( mBuffer.data(), kBufferSize );
+#endif
 }
 
 auto CFileOutStream::fail() const -> bool {