@@ -49,15 +49,16 @@ export function generateFmuCSources(dae: ModelicaDAE, fmuResult: FmuResult, opti
   const vars = fmuResult.scalarVariables;
   const nStates = fmuResult.modelStructure.derivatives.length;
   const nVars = vars.length;
+  const nStringVars = vars.filter((v) => v.type === "String").length;
 
   // ── model.h ──
-  const modelH = generateModelH(id, nVars, nStates, fmuResult);
+  const modelH = generateModelH(id, nVars, nStates, nStringVars, fmuResult);
 
   // ── model.c ──
   const modelC = generateModelC(id, dae, fmuResult);
 
   // ── fmi2Functions.c ──
-  const fmi2FunctionsC = generateFmi2FunctionsC(id, nVars, nStates, fmuResult);
+  const fmi2FunctionsC = generateFmi2FunctionsC(id, nVars, nStates, nStringVars, fmuResult);
 
   // ── CMakeLists.txt ──
   const cmakeLists = generateCMakeLists(id);
@@ -237,7 +238,7 @@ function escapeCString(s: string): string {
 
 // ── File generators ──
 
-function generateModelH(id: string, nVars: number, nStates: number, result: FmuResult): string {
+function generateModelH(id: string, nVars: number, nStates: number, nStringVars: number, result: FmuResult): string {
   const lines: string[] = [];
   lines.push("/* Auto-generated by ModelScript — do not edit */");
   lines.push(`#ifndef ${id.toUpperCase()}_MODEL_H`);
@@ -250,6 +251,7 @@ function generateModelH(id: string, nVars: number, nStates: number, result: FmuR
   lines.push(`#define MODEL_GUID "${result.guid}"`);
   lines.push(`#define N_VARS ${nVars}`);
   lines.push(`#define N_STATES ${nStates}`);
+  lines.push(`#define N_STRING_VARS ${nStringVars}`);
   lines.push(`#define N_EVENT_INDICATORS ${result.numberOfEventIndicators}`);
   lines.push("");
 
@@ -265,6 +267,7 @@ function generateModelH(id: string, nVars: number, nStates: number, result: FmuR
   lines.push("  double vars[N_VARS + 1];  /* +1 for safety */");
   lines.push("  double states[N_STATES + 1];");
   lines.push("  double derivatives[N_STATES + 1];");
+  lines.push("  char* stringVars[N_STRING_VARS + 1];  /* string variable storage */");
   lines.push("  double time;");
   lines.push("  int isDirtyValues;");
   lines.push(`} ${id}_Instance;`);
@@ -376,7 +379,13 @@ function generateModelC(id: string, dae: ModelicaDAE, result: FmuResult): string
   return lines.join("\n");
 }
 
-function generateFmi2FunctionsC(id: string, nVars: number, nStates: number, result: FmuResult): string {
+function generateFmi2FunctionsC(
+  id: string,
+  nVars: number,
+  nStates: number,
+  nStringVars: number,
+  result: FmuResult,
+): string {
   const lines: string[] = [];
   lines.push("/* Auto-generated by ModelScript — FMI 2.0 API implementation */");
   lines.push(`#include "${id}_model.h"`);
@@ -623,18 +632,74 @@ function generateFmi2FunctionsC(id: string, nVars: number, nStates: number, resu
 
   // ── Terminate / FreeInstance ──
   lines.push("fmi2Status fmi2Terminate(fmi2Component c) { (void)c; return fmi2OK; }");
-  lines.push("void fmi2FreeInstance(fmi2Component c) { free(c); }");
+  lines.push("");
+  lines.push("void fmi2FreeInstance(fmi2Component c) {");
+  lines.push("  if (!c) return;");
+  lines.push("  FMUInstance* inst = (FMUInstance*)c;");
+  lines.push("  /* Free all allocated string variables */");
+  lines.push("  for (int i = 0; i < N_STRING_VARS; i++) {");
+  lines.push("    if (inst->model.stringVars[i]) free(inst->model.stringVars[i]);");
+  lines.push("  }");
+  lines.push("  free(inst);");
+  lines.push("}");
   lines.push("");
 
   // ── Stubs for remaining FMI 2.0 functions ──
   lines.push("/* --- Stubs --- */");
   lines.push("fmi2Status fmi2Reset(fmi2Component c) { (void)c; return fmi2OK; }");
-  lines.push(
-    "fmi2Status fmi2SetString(fmi2Component c, const fmi2ValueReference vr[], size_t nvr, const fmi2String value[]) { (void)c; (void)vr; (void)nvr; (void)value; return fmi2OK; }",
-  );
-  lines.push(
-    "fmi2Status fmi2GetString(fmi2Component c, const fmi2ValueReference vr[], size_t nvr, fmi2String value[]) { (void)c; (void)vr; (void)nvr; (void)value; return fmi2OK; }",
-  );
+
+  // ── fmi2SetString / fmi2GetString ──
+  // Build a value-reference → string-index mapping for string variables
+  const stringVarIndices = result.scalarVariables
+    .filter((sv) => sv.type === "String")
+    .map((sv, idx) => ({ vr: sv.valueReference, idx }));
+
+  if (nStringVars > 0) {
+    // Emit a lookup table: VR → string index (-1 if not a string var)
+    lines.push("");
+    lines.push("/* VR-to-string-index mapping */");
+    lines.push(`static int stringVarIndex(fmi2ValueReference vr) {`);
+    lines.push("  switch (vr) {");
+    for (const { vr, idx } of stringVarIndices) {
+      lines.push(`    case ${vr}: return ${idx};`);
+    }
+    lines.push("    default: return -1;");
+    lines.push("  }");
+    lines.push("}");
+    lines.push("");
+
+    lines.push(
+      "fmi2Status fmi2SetString(fmi2Component c, const fmi2ValueReference vr[], size_t nvr, const fmi2String value[]) {",
+    );
+    lines.push("  FMUInstance* inst = (FMUInstance*)c;");
+    lines.push("  for (size_t i = 0; i < nvr; i++) {");
+    lines.push("    int idx = stringVarIndex(vr[i]);");
+    lines.push("    if (idx >= 0) {");
+    lines.push("      if (inst->model.stringVars[idx]) free(inst->model.stringVars[idx]);");
+    lines.push('      inst->model.stringVars[idx] = value[i] ? strdup(value[i]) : strdup("");');
+    lines.push("    }");
+    lines.push("  }");
+    lines.push("  return fmi2OK;");
+    lines.push("}");
+    lines.push("");
+    lines.push(
+      "fmi2Status fmi2GetString(fmi2Component c, const fmi2ValueReference vr[], size_t nvr, fmi2String value[]) {",
+    );
+    lines.push("  FMUInstance* inst = (FMUInstance*)c;");
+    lines.push("  for (size_t i = 0; i < nvr; i++) {");
+    lines.push("    int idx = stringVarIndex(vr[i]);");
+    lines.push('    value[i] = (idx >= 0 && inst->model.stringVars[idx]) ? inst->model.stringVars[idx] : "";');
+    lines.push("  }");
+    lines.push("  return fmi2OK;");
+    lines.push("}");
+  } else {
+    lines.push(
+      "fmi2Status fmi2SetString(fmi2Component c, const fmi2ValueReference vr[], size_t nvr, const fmi2String value[]) { (void)c; (void)vr; (void)nvr; (void)value; return fmi2OK; }",
+    );
+    lines.push(
+      "fmi2Status fmi2GetString(fmi2Component c, const fmi2ValueReference vr[], size_t nvr, fmi2String value[]) { (void)c; (void)vr; (void)nvr; (void)value; return fmi2OK; }",
+    );
+  }
   lines.push(
     "fmi2Status fmi2GetNominalsOfContinuousStates(fmi2Component c, fmi2Real nominals[], size_t nx) { for (size_t i = 0; i < nx; i++) nominals[i] = 1.0; (void)c; return fmi2OK; }",
   );
 
@@ -5,7 +5,11 @@
  *
  * Defines which output variables from one participant feed into
  * which input variables of another participant.
+/**
+ * Value type for co-simulation variable exchange.
+ * Supports all FMI 2.0 scalar types: Real, Integer, Boolean, String.
  */
+export type CosimValue = number | string | boolean;
 
 /** A single variable coupling: one output feeds one input. */
 export interface VariableCoupling {
@@ -66,8 +70,8 @@ export class CouplingGraph {
    * Apply coupling values: given a map of all participant outputs,
    * produce a map of participant ID → input values to inject.
    */
-  applyCouplings(allOutputs: Map<string, Map<string, number>>): Map<string, Map<string, number>> {
-    const inputs = new Map<string, Map<string, number>>();
+  applyCouplings(allOutputs: Map<string, Map<string, CosimValue>>): Map<string, Map<string, CosimValue>> {
+    const inputs = new Map<string, Map<string, CosimValue>>();
 
     for (const coupling of this.couplings) {
       const sourceOutputs = allOutputs.get(coupling.from.participantId);
@@ -78,7 +82,7 @@ export class CouplingGraph {
 
       let targetInputs = inputs.get(coupling.to.participantId);
       if (!targetInputs) {
-        targetInputs = new Map<string, number>();
+        targetInputs = new Map<string, CosimValue>();
         inputs.set(coupling.to.participantId, targetInputs);
       }
       targetInputs.set(coupling.to.variableName, value);
 
@@ -78,7 +78,7 @@ export interface SetInputsCommand {
   /** Participant ID. */
   participantId: string;
   /** Variable name → value map. */
-  values: Record<string, number>;
+  values: Record<string, number | string | boolean>;
 }
 
 /** Terminate command. */
@@ -118,7 +118,7 @@ export interface StatusMessage {
   /** Error message (when state is 'error'). */
   error?: string | undefined;
   /** Output variable values (after step). */
-  outputs?: Record<string, number> | undefined;
+  outputs?: Record<string, number | string | boolean> | undefined;
 }
 
 // ── Result messages ──
@@ -128,7 +128,7 @@ export interface StepResult {
   /** Simulation time. */
   time: number;
   /** Participant ID → variable values map. */
-  participants: Record<string, Record<string, number>>;
+  participants: Record<string, Record<string, number | string | boolean>>;
 }
 
 // ── Batched variable data ──
@@ -138,7 +138,7 @@ export interface VariableBatch {
   /** Simulation time. */
   time: number;
   /** Variable name → value map. */
-  values: Record<string, number>;
+  values: Record<string, number | string | boolean>;
 }
 
 // ── Serialization helpers ──
 
@@ -98,7 +98,7 @@ export class Orchestrator {
         const effectiveH = Math.min(h, experiment.stopTime - t);
 
         // ── Step 2a: Collect all current outputs ──
-        const allOutputs = new Map<string, Map<string, number>>();
+        const allOutputs = new Map<string, Map<string, number | string | boolean>>();
         for (const p of participants) {
           const outputs = await p.getOutputs();
           allOutputs.set(p.id, outputs);
@@ -121,10 +121,10 @@ export class Orchestrator {
         }
 
         // ── Step 2e: Collect outputs and publish results ──
-        const stepOutputs: Record<string, Record<string, number>> = {};
+        const stepOutputs: Record<string, Record<string, number | string | boolean>> = {};
         for (const p of participants) {
           const outputs = await p.getOutputs();
-          const map: Record<string, number> = {};
+          const map: Record<string, number | string | boolean> = {};
           outputs.forEach((value, key) => {
             map[key] = value;
           });
 
@@ -7,6 +7,7 @@
  * must implement to participate in a co-simulation session.
  */
 
+import type { CosimValue } from "./coupling.js";
 import type { ParticipantMetadata } from "./mqtt/protocol.js";
 
 /**
@@ -46,13 +47,13 @@ export interface CoSimParticipant {
    * Get current output variable values.
    * Called after doStep() to read results.
    */
-  getOutputs(): Promise<Map<string, number>>;
+  getOutputs(): Promise<Map<string, CosimValue>>;
 
   /**
    * Set input variable values before the next step.
    * Called before doStep() to provide coupled values.
    */
-  setInputs(values: Map<string, number>): Promise<void>;
+  setInputs(values: Map<string, CosimValue>): Promise<void>;
 
   /**
    * Terminate the participant and release resources.