diff --git a/core/src/main/java/org/teavm/backend/c/CTarget.java b/core/src/main/java/org/teavm/backend/c/CTarget.java
index fbdaf861d..c3de9c33c 100644
--- a/core/src/main/java/org/teavm/backend/c/CTarget.java
+++ b/core/src/main/java/org/teavm/backend/c/CTarget.java
@@ -346,7 +346,9 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
 
         for (String className : classNames) {
             ClassHolder cls = classes.get(className);
-            classGenerator.generateClass(cls);
+            if (cls != null) {
+                classGenerator.generateClass(cls);
+            }
         }
 
         classGenerator.generateRemainingData(classNames, shadowStackTransformer);
@@ -369,8 +371,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
                     if (parent == null) {
                         parent = RuntimeObject.class.getName();
                     }
-                    if (!parent.equals(Structure.class.getName())
-                            && stateMap.getOrDefault(cls.getParent(), (byte) 0) == 0) {
+                    if (!parent.equals(Structure.class.getName()) && stateMap.getOrDefault(parent, (byte) 0) == 0) {
                         stack.push(parent);
                     }
                     break;
diff --git a/core/src/main/java/org/teavm/backend/c/generate/ClassGenerator.java b/core/src/main/java/org/teavm/backend/c/generate/ClassGenerator.java
index 7c1156165..bcbf6c6a3 100644
--- a/core/src/main/java/org/teavm/backend/c/generate/ClassGenerator.java
+++ b/core/src/main/java/org/teavm/backend/c/generate/ClassGenerator.java
@@ -491,6 +491,9 @@ public class ClassGenerator {
     }
 
     private void generateVirtualTableStructure(ClassReader cls) {
+        if (cls == null) {
+            return;
+        }
         String name = context.getNames().forClassClass(cls.getName());
 
         vtableStructuresWriter.print("typedef struct ").print(name).println(" {").indent();
diff --git a/core/src/main/java/org/teavm/backend/c/generate/CodeGenerationVisitor.java b/core/src/main/java/org/teavm/backend/c/generate/CodeGenerationVisitor.java
index cf818dab6..82902bff3 100644
--- a/core/src/main/java/org/teavm/backend/c/generate/CodeGenerationVisitor.java
+++ b/core/src/main/java/org/teavm/backend/c/generate/CodeGenerationVisitor.java
@@ -60,9 +60,11 @@ import org.teavm.backend.c.intrinsic.IntrinsicContext;
 import org.teavm.diagnostics.Diagnostics;
 import org.teavm.interop.Address;
 import org.teavm.interop.c.Include;
+import org.teavm.interop.c.Variable;
 import org.teavm.model.AnnotationContainerReader;
 import org.teavm.model.AnnotationReader;
 import org.teavm.model.AnnotationValue;
+import org.teavm.model.CallLocation;
 import org.teavm.model.ClassReader;
 import org.teavm.model.ElementModifier;
 import org.teavm.model.FieldReference;
@@ -469,6 +471,7 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
         for (int i = 0; i < expr.getArguments().size(); ++i) {
             temporaries.add(allocTemporaryVariable(CVariableType.PTR));
         }
+        boolean stringResult = method.getResultType().isObject(String.class);
 
         writer.print("(");
         for (int i = 0; i < expr.getArguments().size(); ++i) {
@@ -482,6 +485,10 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
                 expr.getArguments().get(i).acceptVisitor(this);
                 writer.print(")");
                 stringTemporaries.add(tmp);
+            } else if (isPrimitiveArray(type)) {
+                writer.print("ARRAY_DATA(");
+                expr.getArguments().get(i).acceptVisitor(this);
+                writer.print(", ").printStrictType(((ValueType.Array) type).getItemType()).print(")");
             } else {
                 expr.getArguments().get(i).acceptVisitor(this);
             }
@@ -492,28 +499,49 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
         if (resultTmp != null) {
             writer.print(resultTmp + " = ");
         }
-        writer.print(names.forMethod(method.getReference())).print("(");
-        for (int i = 0; i < temporaries.size(); ++i) {
-            if (i > 0) {
-                writer.print(", ");
+        writer.print(names.forMethod(method.getReference()));
+        if (method.getAnnotations().get(Variable.class.getName()) == null) {
+            writer.print("(");
+            for (int i = 0; i < temporaries.size(); ++i) {
+                if (i > 0) {
+                    writer.print(", ");
+                }
+                writer.print(temporaries.get(i));
+                freeTemporaryVariable(CVariableType.PTR);
             }
-            writer.print(temporaries.get(i));
-            freeTemporaryVariable(CVariableType.PTR);
+            writer.print(")");
+        } else if (method.parameterCount() > 0 || method.getResultType() == ValueType.VOID) {
+            context.getDiagnostics().error(new CallLocation(method.getReference()),
+                    "'@Variable' annotation is not applicable to method {{m0}}", method.getReference());
         }
-        writer.print(")");
 
         for (String tmp : stringTemporaries) {
             writer.print(", teavm_free(" + tmp + ")");
         }
 
         if (resultTmp != null) {
-            writer.print(", " + resultTmp);
+            writer.print(", ");
+            if (stringResult) {
+                writer.print("teavm_cToString(");
+            }
+            writer.print(resultTmp);
+            if (stringResult) {
+                writer.print(")");
+            }
             freeTemporaryVariable(typeToCType(method.getResultType()));
         }
 
         writer.print(")");
     }
 
+    private static boolean isPrimitiveArray(ValueType type) {
+        if (!(type instanceof ValueType.Array)) {
+            return false;
+        }
+
+        return ((ValueType.Array) type).getItemType() instanceof ValueType.Primitive;
+    }
+
     private boolean isWrappedNativeCall(MethodReader method) {
         if (!method.hasModifier(ElementModifier.NATIVE)) {
             return false;
diff --git a/core/src/main/java/org/teavm/backend/c/intrinsic/StringsIntrinsic.java b/core/src/main/java/org/teavm/backend/c/intrinsic/StringsIntrinsic.java
new file mode 100644
index 000000000..2fc862f4d
--- /dev/null
+++ b/core/src/main/java/org/teavm/backend/c/intrinsic/StringsIntrinsic.java
@@ -0,0 +1,43 @@
+/*
+ *  Copyright 2019 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.c.intrinsic;
+
+import org.teavm.ast.InvocationExpr;
+import org.teavm.interop.Strings;
+import org.teavm.model.MethodReference;
+
+public class StringsIntrinsic implements Intrinsic {
+    @Override
+    public boolean canHandle(MethodReference method) {
+        return method.getClassName().equals(Strings.class.getName());
+    }
+
+    @Override
+    public void apply(IntrinsicContext context, InvocationExpr invocation) {
+        switch (invocation.getMethod().getName()) {
+            case "toC":
+                context.writer().print("teavm_stringToC(");
+                context.emit(invocation.getArguments().get(0));
+                context.writer().print(")");
+                break;
+            case "fromC":
+                context.writer().print("teavm_cToString(");
+                context.emit(invocation.getArguments().get(0));
+                context.writer().print(")");
+                break;
+        }
+    }
+}
diff --git a/interop/core/src/main/java/org/teavm/interop/Strings.java b/interop/core/src/main/java/org/teavm/interop/Strings.java
new file mode 100644
index 000000000..2831c2d1f
--- /dev/null
+++ b/interop/core/src/main/java/org/teavm/interop/Strings.java
@@ -0,0 +1,25 @@
+/*
+ *  Copyright 2019 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.interop;
+
+public final class Strings {
+    private Strings() {
+    }
+
+    public static native Address toC(String javaString);
+
+    public static native String fromC(Address cString);
+}
diff --git a/interop/core/src/main/java/org/teavm/interop/c/Variable.java b/interop/core/src/main/java/org/teavm/interop/c/Variable.java
new file mode 100644
index 000000000..5a753175b
--- /dev/null
+++ b/interop/core/src/main/java/org/teavm/interop/c/Variable.java
@@ -0,0 +1,26 @@
+/*
+ *  Copyright 2019 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.interop.c;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.METHOD)
+public @interface Variable {
+}