Filesystem abstraction prototype - Make paths relative

p-filesystem.cc

@@ -290,9 +290,42 @@ bool T_FSPath::isAbove(
 
 /*----------------------------------------------------------------------------*/
 
+T_FSPath T_FSPath::makeRelative(
+		T_FSPath const& relTo ) const noexcept
+{
+	assert( isValid( ) && relTo.isValid( ) );
+	assert( isCanonical( ) && relTo.isCanonical( ) );
+	if ( relTo.root_ != root_ ) {
+		return *this;
+	}
+
+	const auto nca{ components_.size( ) } ,
+		ncb{ relTo.components_.size( ) } ,
+		nc{ std::min( nca , ncb ) };
+	uint32_t nCommon{ 0u };
+	for ( auto i = 0u ; i < nc ; i ++ ) {
+		if ( M_CMPSTR_( components_[ i ] , relTo.components_[ i ] ) != 0 ) {
+			break;
+		}
+		nCommon ++;
+	}
+
+	T_FSPath np;
+	const T_String parent{ T_String::Pooled( ".." ) };
+	for ( auto i = nca ; i > nCommon ; i -- ) {
+		np.components_.add( parent );
+	}
+	for ( auto i = nCommon ; i < nca ; i ++ ) {
+		np.components_.add( components_[ i ] );
+	}
+	return np;
+}
+
+/*----------------------------------------------------------------------------*/
+
 bool T_FSPath::isCanonical( ) const noexcept
 {
-	if ( !valid_ ) {
+	if ( !( valid_ && root_ ) ) {
 		return false;
 	}
 
@@ -308,7 +341,7 @@ bool T_FSPath::isCanonical( ) const noexcept
 T_FSPath T_FSPath::canonical( ) const noexcept
 {
 	auto const nc{ components_.size( ) };
-	if ( !( valid_ && nc ) ) {
+	if ( !( valid_ && nc && root_ ) ) {
 		return *this;
 	}
 

p-filesystem.hh

@@ -102,6 +102,11 @@ class T_FSPath
 	// Checks if the current path is a child of the specified path
 	bool isUnder( T_FSPath const& other ) const noexcept;
 
+	// Create a relative path based on the current path and a "parent" path.
+	// Both paths must be canonical and valid. If they have different roots,
+	// a copy of the current path will be returned.
+	T_FSPath makeRelative( T_FSPath const& relTo ) const noexcept;
+
 	//----------------------------------------------------------------------
 
 	// Checks whether the specified path is canonical