diff --git a/include/verilated_heavy.h b/include/verilated_heavy.h
index f85072ec8..94759fe1a 100644
--- a/include/verilated_heavy.h
+++ b/include/verilated_heavy.h
@@ -66,7 +66,7 @@ extern IData VL_FOPEN_NI(const std::string& filename, IData mode) VL_MT_SAFE;
 extern void VL_READMEM_N(bool hex, int width, int depth, int array_lsb, int fnwords,
                          const std::string& ofilename, void* memp, IData start, IData end) VL_MT_SAFE;
 extern IData VL_SSCANF_INX(int lbits, const std::string& ld, const char* formatp, ...) VL_MT_SAFE;
-extern void VL_SFORMAT_X(int obits_ignored, std::string &output, const char* formatp, ...) VL_MT_SAFE;
+extern void VL_SFORMAT_X(int obits_ignored, std::string& output, const char* formatp, ...) VL_MT_SAFE;
 extern std::string VL_SFORMATF_NX(const char* formatp, ...) VL_MT_SAFE;
 extern IData VL_VALUEPLUSARGS_INW(int rbits, const std::string& ld, WDataOutP rdp) VL_MT_SAFE;
 inline IData VL_VALUEPLUSARGS_INI(int rbits, const std::string& ld, IData& rdr) VL_MT_SAFE {
diff --git a/include/verilated_vpi.cpp b/include/verilated_vpi.cpp
index 0679bc6f7..b46ae243c 100644
--- a/include/verilated_vpi.cpp
+++ b/include/verilated_vpi.cpp
@@ -459,7 +459,7 @@ public:
         m_errorInfo.level = level;
         return this;
     }
-    void setMessage(std::string file, PLI_INT32 line, std::string message, ...) {
+    void setMessage(std::string file, PLI_INT32 line, const std::string& message, ...) {
         static VL_THREAD_LOCAL std::string filehold;
         va_list args;
         va_start(args, message);
diff --git a/src/V3CCtors.cpp b/src/V3CCtors.cpp
index 5f9f6fc67..97920a280 100644
--- a/src/V3CCtors.cpp
+++ b/src/V3CCtors.cpp
@@ -77,7 +77,8 @@ public:
 	m_numStmts += 1;
     }
 
-    V3CCtorsVisitor(AstNodeModule* nodep, string basename, string argsp="", string callargsp="",
+    V3CCtorsVisitor(AstNodeModule* nodep, const string& basename,
+		    const string& argsp="", const string& callargsp="",
 		    const string& stmt="") {
 	m_basename = basename;
 	m_argsp = argsp;
diff --git a/src/V3Config.cpp b/src/V3Config.cpp
index 609cc92ef..d23cc2c95 100644
--- a/src/V3Config.cpp
+++ b/src/V3Config.cpp
@@ -144,7 +144,7 @@ V3ConfigIgnores V3ConfigIgnores::s_singleton;
 //######################################################################
 // V3Config
 
-void V3Config::addIgnore(V3ErrorCode code, bool on, string filename, int min, int max) {
+void V3Config::addIgnore(V3ErrorCode code, bool on, const string& filename, int min, int max) {
     if (filename=="*") {
 	FileLine::globalWarnOff(code,!on);
     } else {
diff --git a/src/V3Config.h b/src/V3Config.h
index a72a3c135..996cdea99 100644
--- a/src/V3Config.h
+++ b/src/V3Config.h
@@ -30,7 +30,7 @@
 
 class V3Config {
 public:
-    static void addIgnore(V3ErrorCode code, bool on, string filename, int min, int max);
+    static void addIgnore(V3ErrorCode code, bool on, const string& filename, int min, int max);
     static void applyIgnores(FileLine* filelinep);
 };
 
diff --git a/src/V3EmitC.cpp b/src/V3EmitC.cpp
index 735e14713..8590eeb81 100644
--- a/src/V3EmitC.cpp
+++ b/src/V3EmitC.cpp
@@ -978,7 +978,6 @@ class EmitCImp : EmitCStmts {
     void emitStaticDecl(AstNodeModule* modp);
     void emitWrapEval(AstNodeModule* modp);
     void emitInt(AstNodeModule* modp);
-    void writeMakefile(string filename);
 
 public:
     EmitCImp() {
diff --git a/src/V3GraphDfa.cpp b/src/V3GraphDfa.cpp
index 268df2786..bc07b1b2d 100644
--- a/src/V3GraphDfa.cpp
+++ b/src/V3GraphDfa.cpp
@@ -69,7 +69,12 @@ private:
     // MEMBERS
     uint32_t		m_step;		// Processing step, so we can avoid clearUser all the time
     HashMap		m_hashMap;	// Dfa Vertex for each set of NFA vertexes
+
+#ifdef VL_CPPCHECK
+    static int debug() { return 9; }
+#else
     static int debug() { return 0; }
+#endif
 
     // METHODS
     DfaGraph* graphp() { return static_cast<DfaGraph*>(m_graphp); }
diff --git a/src/V3LinkDot.cpp b/src/V3LinkDot.cpp
index b690cebf8..e08c9bb4c 100644
--- a/src/V3LinkDot.cpp
+++ b/src/V3LinkDot.cpp
@@ -604,7 +604,7 @@ class LinkDotFindVisitor : public AstNVisitor {
     // METHODS
     int debug() { return LinkDotState::debug(); }
 
-    virtual AstConst* parseParamLiteral(FileLine* fl, string literal) {
+    virtual AstConst* parseParamLiteral(FileLine* fl, const string& literal) {
 	bool success = false;
         if (literal[0] == '"') {
 	    // This is a string
@@ -2110,10 +2110,8 @@ private:
 		}
 		dotSymp = m_statep->findDotted(dotSymp, nodep->dotted(), baddot, okSymp); // Maybe NULL
 	    }
-	    VSymEnt* foundp = NULL;
-	    AstNodeFTask* taskp = NULL;
-	    foundp = m_statep->findSymPrefixed(dotSymp, nodep->name(), baddot);
-	    taskp = foundp ? foundp->nodep()->castNodeFTask() : NULL; // Maybe NULL
+	    VSymEnt* foundp = m_statep->findSymPrefixed(dotSymp, nodep->name(), baddot);
+	    AstNodeFTask* taskp = foundp ? foundp->nodep()->castNodeFTask() : NULL; // Maybe NULL
 	    if (taskp) {
 		nodep->taskp(taskp);
 		nodep->packagep(foundp->packagep());
diff --git a/src/V3Localize.cpp b/src/V3Localize.cpp
index 1318fc4bf..6313fbf91 100644
--- a/src/V3Localize.cpp
+++ b/src/V3Localize.cpp
@@ -66,6 +66,7 @@ protected:
 	    int m_stdFuncAsn:1;	// Found simple assignment
 	    int m_done:1;	// Removed
 	};
+        // cppcheck-suppress unusedStructMember
 	uint32_t m_flags;
 	VarFlags(AstNode* nodep) { m_flags = nodep->user2(); }
 	void setNodeFlags(AstNode* nodep) { nodep->user2(m_flags); }
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index ec4d6a799..cc1f3aae9 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -155,11 +155,11 @@ void V3Options::addParameter(const string& paramline, bool allowPlus) {
     }
 }
 
-bool V3Options::hasParameter(string name) {
+bool V3Options::hasParameter(const string& name) {
     return m_parameters.find(name) != m_parameters.end();
 }
 
-string V3Options::parameter(string name) {
+string V3Options::parameter(const string& name) {
     string value = m_parameters.find(name)->second;
     m_parameters.erase(m_parameters.find(name));
     return value;
diff --git a/src/V3Options.h b/src/V3Options.h
index 510827536..de2996915 100644
--- a/src/V3Options.h
+++ b/src/V3Options.h
@@ -293,8 +293,8 @@ class V3Options {
     const V3StringList& forceIncs() const { return m_forceIncs; }
     const V3LangCode& defaultLanguage() const { return m_defaultLanguage; }
 
-    bool hasParameter(string name);
-    string parameter(string name);
+    bool hasParameter(const string& name);
+    string parameter(const string& name);
     void checkParameters();
 
     bool isFuture(const string& flag) const;
diff --git a/src/V3Task.cpp b/src/V3Task.cpp
index 6acfc86e1..e20505ea9 100644
--- a/src/V3Task.cpp
+++ b/src/V3Task.cpp
@@ -795,7 +795,7 @@ private:
         makePortList(nodep, rtnvarp, dpip);
     }
 
-    bool duplicatedDpiProto(AstNodeFTask* nodep, string dpiproto) {
+    bool duplicatedDpiProto(AstNodeFTask* nodep, const string& dpiproto) {
         // Only create one DPI extern prototype for each specified cname
         // as it's legal for the user to attach multiple tasks to one dpi cname
         DpiNames::iterator iter = m_dpiNames.find(nodep->cname());
diff --git a/src/V3Unroll.cpp b/src/V3Unroll.cpp
index dcfd17781..b50115e5f 100644
--- a/src/V3Unroll.cpp
+++ b/src/V3Unroll.cpp
@@ -455,7 +455,7 @@ private:
 
 public:
     // CONSTUCTORS
-    UnrollVisitor(AstNode* nodep, bool generate, string beginName) {
+    UnrollVisitor(AstNode* nodep, bool generate, const string& beginName) {
 	m_forVarp = NULL;
 	m_forVscp = NULL;
 	m_ignoreIncp = NULL;
@@ -481,7 +481,7 @@ void V3Unroll::unrollAll(AstNetlist* nodep) {
     V3Global::dumpCheckGlobalTree("unroll", 0, v3Global.opt.dumpTreeLevel(__FILE__) >= 3);
 }
 
-void V3Unroll::unrollGen(AstNodeFor* nodep, string beginName) {
+void V3Unroll::unrollGen(AstNodeFor* nodep, const string& beginName) {
     UINFO(2,__FUNCTION__<<": "<<endl);
     UnrollVisitor visitor (nodep, true, beginName);
 }
diff --git a/src/V3Unroll.h b/src/V3Unroll.h
index c26d664d6..1d17cd23b 100644
--- a/src/V3Unroll.h
+++ b/src/V3Unroll.h
@@ -30,7 +30,7 @@
 class V3Unroll {
 public:
     static void unrollAll(AstNetlist* nodep);
-    static void unrollGen(AstNodeFor* nodep, string beginName);
+    static void unrollGen(AstNodeFor* nodep, const string& beginName);
 };
 
 #endif // Guard
diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index 8ad255a08..dd66e32d6 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -3155,8 +3155,7 @@ private:
 	} else {
 	    bool bad = widthBad(underp,nodep->findLogicBoolDType());
 	    if (bad) {
-		bool warnOn = true; // Not used
-		if (warnOn) {
+                {  // if (warnOn), but not needed here
 		    if (debug()>4) nodep->backp()->dumpTree(cout,"  back: ");
 		    nodep->v3warn(WIDTH,"Logical Operator "<<nodep->prettyTypeName()
 				  <<" expects 1 bit on the "<<side<<", but "<<side<<"'s "