diff --git a/src/StaticPHP/Package/PhpExtensionPackage.php b/src/StaticPHP/Package/PhpExtensionPackage.php
index 8fb63ece..c638114d 100644
--- a/src/StaticPHP/Package/PhpExtensionPackage.php
+++ b/src/StaticPHP/Package/PhpExtensionPackage.php
@@ -286,7 +286,7 @@ class PhpExtensionPackage extends Package
         }
         return [
             'CFLAGS' => $config['cflags'],
-            'CXXFLAGS' => $config['cflags'],
+            'CXXFLAGS' => $config['cxxflags'],
             'LDFLAGS' => $ldflags,
             'LIBS' => clean_spaces("{$preStatic} {$staticLibs} {$postStatic} {$sharedLibs}"),
             'LD_LIBRARY_PATH' => BUILD_LIB_PATH,
diff --git a/src/StaticPHP/Util/SPCConfigUtil.php b/src/StaticPHP/Util/SPCConfigUtil.php
index fd2460ee..ef69f023 100644
--- a/src/StaticPHP/Util/SPCConfigUtil.php
+++ b/src/StaticPHP/Util/SPCConfigUtil.php
@@ -37,83 +37,12 @@ class SPCConfigUtil
     public function config(array $packages = [], bool $include_suggests = false): array
     {
         // if have php, make php as all extension's dependency
-        if (!$this->no_php) {
-            $dep_override = ['php' => array_filter($packages, fn ($y) => str_starts_with($y, 'ext-'))];
-        } else {
-            $dep_override = [];
-        }
-        $resolved = DependencyResolver::resolve($packages, $dep_override, $include_suggests);
-
-        $ldflags = $this->getLdflagsString();
-        $cflags = $this->getIncludesString($resolved);
-        $libs = $this->getLibsString($resolved, !$this->absolute_libs);
-
-        // additional OS-specific libraries (e.g. macOS -lresolv)
-        // embed
-        if ($extra_libs = SystemTarget::getRuntimeLibs()) {
-            $libs .= " {$extra_libs}";
-        }
-
-        $extra_env = getenv('SPC_EXTRA_LIBS');
-        if (is_string($extra_env) && !empty($extra_env)) {
-            $libs .= " {$extra_env}";
-        }
-        // package frameworks
-        if (SystemTarget::getTargetOS() === 'Darwin') {
-            $libs .= " {$this->getFrameworksString($resolved)}";
-        }
-        // C++
-        if ($this->hasCpp($resolved)) {
-            $target_os = SystemTarget::getTargetOS();
-            if ($target_os === 'Darwin') {
-                $libcpp = '-lc++';
-                $libs = str_replace($libcpp, '', $libs) . " {$libcpp}";
-            } elseif ($target_os !== 'Windows') {
-                // Linux and other Unix-like systems use libstdc++
-                $libcpp = '-lstdc++';
-                $libs = str_replace($libcpp, '', $libs) . " {$libcpp}";
-            }
-            // Windows (MSVC): C++ runtime is linked automatically, no explicit lib needed
-        }
-
-        if ($this->libs_only_deps) {
-            // mimalloc must come first
-            if (in_array('mimalloc', $resolved) && file_exists(BUILD_LIB_PATH . '/libmimalloc.a')) {
-                $libs = BUILD_LIB_PATH . '/libmimalloc.a ' . str_replace([BUILD_LIB_PATH . '/libmimalloc.a', '-lmimalloc'], ['', ''], $libs);
-            }
-            return [
-                'cflags' => clean_spaces(getenv('CFLAGS') . ' ' . $cflags),
-                'ldflags' => clean_spaces(getenv('LDFLAGS') . ' ' . $ldflags),
-                'libs' => clean_spaces(getenv('LIBS') . ' ' . $libs),
-            ];
-        }
-
-        // embed
-        if (!$this->no_php) {
-            if (SystemTarget::getTargetOS() === 'Windows') {
-                // Windows: use php8embed.lib directly (either full path or short name)
-                $major = intdiv(PHP_VERSION_ID, 10000);
-                $php_lib = $this->absolute_libs ? BUILD_LIB_PATH . "\\php{$major}embed.lib" : "php{$major}embed.lib";
-                // Windows system libs required by PHP
-                // Use same system libs as PHP Makefile: LIBS=kernel32.lib ole32.lib user32.lib advapi32.lib shell32.lib ws2_32.lib Dnsapi.lib psapi.lib bcrypt.lib
-                $libs = "{$php_lib} {$libs} kernel32.lib ole32.lib user32.lib advapi32.lib shell32.lib ws2_32.lib dnsapi.lib psapi.lib bcrypt.lib";
-            } else {
-                $libs = "-lphp {$libs} -lc";
-            }
-        }
-
-        $allLibs = getenv('LIBS') . ' ' . $libs;
-
-        // mimalloc must come first
-        if (in_array('mimalloc', $resolved) && file_exists(BUILD_LIB_PATH . '/libmimalloc.a')) {
-            $allLibs = BUILD_LIB_PATH . '/libmimalloc.a ' . str_replace([BUILD_LIB_PATH . '/libmimalloc.a', '-lmimalloc'], ['', ''], $allLibs);
-        }
-
-        return [
-            'cflags' => clean_spaces(getenv('CFLAGS') . ' ' . $cflags),
-            'ldflags' => clean_spaces(getenv('LDFLAGS') . ' ' . $ldflags),
-            'libs' => clean_spaces($allLibs),
-        ];
+        $dep_override = $this->no_php
+            ? []
+            : ['php' => array_filter($packages, fn ($y) => str_starts_with($y, 'ext-'))];
+        return $this->configWithResolvedPackages(
+            DependencyResolver::resolve($packages, $dep_override, $include_suggests)
+        );
     }
 
     /**
@@ -127,6 +56,7 @@ class SPCConfigUtil
      * @param array|PhpExtensionPackage $extension_packages Extension instance or list
      * @return array{
      *     cflags: string,
+     *     cxxflags: string,
      *     ldflags: string,
      *     libs: string
      * }
@@ -150,6 +80,7 @@ class SPCConfigUtil
      * @param array|LibraryPackage $lib Library instance or list
      * @return array{
      *     cflags: string,
+     *     cxxflags: string,
      *     ldflags: string,
      *     libs: string
      * }
@@ -180,6 +111,7 @@ class SPCConfigUtil
      * @param string[] $resolved_packages The full resolved package list
      * @return array{
      *     cflags: string,
+     *     cxxflags: string,
      *     ldflags: string,
      *     libs: string
      * }
@@ -192,6 +124,7 @@ class SPCConfigUtil
         if (empty($sub_deps)) {
             return [
                 'cflags' => '',
+                'cxxflags' => '',
                 'ldflags' => '',
                 'libs' => '',
             ];
@@ -212,11 +145,12 @@ class SPCConfigUtil
     }
 
     /**
-     * Get configuration using already-resolved packages (skip dependency resolution).
+     * Build cflags/cxxflags/ldflags/libs for an already-resolved package set (skip dependency resolution).
      *
-     * @param string[] $resolved_packages Already resolved package names in build order
+     * @param string[] $resolved_packages Resolved package names in build order
      * @return array{
      *     cflags: string,
+     *     cxxflags: string,
      *     ldflags: string,
      *     libs: string
      * }
@@ -224,9 +158,14 @@ class SPCConfigUtil
     public function configWithResolvedPackages(array $resolved_packages): array
     {
         $ldflags = $this->getLdflagsString();
-        $cflags = $this->getIncludesString($resolved_packages);
+        $includes = $this->getIncludesString($resolved_packages);
         $libs = $this->getLibsString($resolved_packages, !$this->absolute_libs);
 
+        // includes (-I…) are language-agnostic — same source for cflags/cxxflags, swap only the env names
+        $cflags = deduplicate_flags(clean_spaces((getenv('SPC_DEFAULT_CFLAGS') ?: '') . ' ' . getenv('CFLAGS') . ' ' . $includes));
+        $cxxflags = deduplicate_flags(clean_spaces((getenv('SPC_DEFAULT_CXXFLAGS') ?: '') . ' ' . getenv('CXXFLAGS') . ' ' . $includes));
+        $ldflags = deduplicate_flags(clean_spaces((getenv('SPC_DEFAULT_LDFLAGS') ?: '') . ' ' . getenv('LDFLAGS') . ' ' . $ldflags));
+
         // additional OS-specific libraries (e.g. macOS -lresolv)
         if ($extra_libs = SystemTarget::getRuntimeLibs()) {
             $libs .= " {$extra_libs}";
@@ -262,15 +201,25 @@ class SPCConfigUtil
                 $libs = BUILD_LIB_PATH . '/libmimalloc.a ' . str_replace([BUILD_LIB_PATH . '/libmimalloc.a', '-lmimalloc'], ['', ''], $libs);
             }
             return [
-                'cflags' => clean_spaces(getenv('CFLAGS') . ' ' . $cflags),
-                'ldflags' => clean_spaces(getenv('LDFLAGS') . ' ' . $ldflags),
+                'cflags' => $cflags,
+                'cxxflags' => $cxxflags,
+                'ldflags' => $ldflags,
                 'libs' => clean_spaces(getenv('LIBS') . ' ' . $libs),
             ];
         }
 
         // embed
         if (!$this->no_php) {
-            $libs = "-lphp {$libs} -lc";
+            if (SystemTarget::getTargetOS() === 'Windows') {
+                // Windows: use php8embed.lib directly (either full path or short name)
+                $major = intdiv(PHP_VERSION_ID, 10000);
+                $php_lib = $this->absolute_libs ? BUILD_LIB_PATH . "\\php{$major}embed.lib" : "php{$major}embed.lib";
+                // Windows system libs required by PHP
+                // Use same system libs as PHP Makefile: LIBS=kernel32.lib ole32.lib user32.lib advapi32.lib shell32.lib ws2_32.lib Dnsapi.lib psapi.lib bcrypt.lib
+                $libs = "{$php_lib} {$libs} kernel32.lib ole32.lib user32.lib advapi32.lib shell32.lib ws2_32.lib dnsapi.lib psapi.lib bcrypt.lib";
+            } else {
+                $libs = "-lphp {$libs} -lc";
+            }
         }
 
         $allLibs = getenv('LIBS') . ' ' . $libs;
@@ -281,8 +230,9 @@ class SPCConfigUtil
         }
 
         return [
-            'cflags' => clean_spaces(getenv('CFLAGS') . ' ' . $cflags),
-            'ldflags' => clean_spaces(getenv('LDFLAGS') . ' ' . $ldflags),
+            'cflags' => $cflags,
+            'cxxflags' => $cxxflags,
+            'ldflags' => $ldflags,
             'libs' => clean_spaces($allLibs),
         ];
     }