diff --git a/src/V3Ast.cpp b/src/V3Ast.cpp
index 33aeda69c..b20a3b184 100644
--- a/src/V3Ast.cpp
+++ b/src/V3Ast.cpp
@@ -974,9 +974,7 @@ std::ostream& operator<<(std::ostream& os, const V3Hash& rhs) {
 
 V3Hash::V3Hash(const string& name) {
     uint32_t val = 0;
-    for (string::const_iterator it = name.begin(); it != name.end(); ++it) {
-        val = val * 31 + *it;
-    }
+    for (const auto& c : name) val = val * 31 + c;
     setBoth(1, val);
 }
 
diff --git a/src/V3AstNodes.cpp b/src/V3AstNodes.cpp
index 2e7ee6406..4762b37fe 100644
--- a/src/V3AstNodes.cpp
+++ b/src/V3AstNodes.cpp
@@ -632,9 +632,7 @@ AstVar* AstVar::scVarRecurse(AstNode* nodep) {
 string AstVar::mtasksString() const {
     std::ostringstream os;
     os << "all: ";
-    for (MTaskIdSet::const_iterator it = m_mtaskIds.begin(); it != m_mtaskIds.end(); ++it) {
-        os << *it << " ";
-    }
+    for (const auto& id : m_mtaskIds) os << id << " ";
     return os.str();
 }
 
diff --git a/src/V3Config.cpp b/src/V3Config.cpp
index d801d901b..ba2acd323 100644
--- a/src/V3Config.cpp
+++ b/src/V3Config.cpp
@@ -170,10 +170,7 @@ public:
     void update(const V3ConfigModule& m) {
         m_tasks.update(m.m_tasks);
         m_vars.update(m.m_vars);
-        for (StringSet::const_iterator it = m.m_coverageOffBlocks.begin();
-             it != m.m_coverageOffBlocks.end(); ++it) {
-            m_coverageOffBlocks.insert(*it);
-        }
+        for (const string& i : m.m_coverageOffBlocks) m_coverageOffBlocks.insert(i);
         if (!m_inline) {
             m_inline = m.m_inline;
             m_inlineValue = m.m_inlineValue;
@@ -210,9 +207,8 @@ public:
     void applyBlock(AstNodeBlock* nodep) {
         AstPragmaType pragma = AstPragmaType::COVERAGE_BLOCK_OFF;
         if (!nodep->unnamed()) {
-            for (StringSet::const_iterator it = m_coverageOffBlocks.begin();
-                 it != m_coverageOffBlocks.end(); ++it) {
-                if (VString::wildmatch(nodep->name(), *it)) {
+            for (const string& i : m_coverageOffBlocks) {
+                if (VString::wildmatch(nodep->name(), i)) {
                     nodep->addStmtsp(new AstPragma(nodep->fileline(), pragma));
                 }
             }
diff --git a/src/V3Const.cpp b/src/V3Const.cpp
index 8dae74a3c..b93b4ef8b 100644
--- a/src/V3Const.cpp
+++ b/src/V3Const.cpp
@@ -2013,8 +2013,7 @@ private:
             bool inPct = false;
             AstNode* argp = nodep->exprsp();
             string text = nodep->text();
-            for (string::const_iterator it = text.begin(); it != text.end(); ++it) {
-                char ch = *it;
+            for (const char ch : text) {
                 if (!inPct && ch == '%') {
                     inPct = true;
                     fmt = ch;
diff --git a/src/V3EmitC.cpp b/src/V3EmitC.cpp
index cb862c6c5..e73709d7a 100644
--- a/src/V3EmitC.cpp
+++ b/src/V3EmitC.cpp
@@ -2828,10 +2828,7 @@ void EmitCStmts::emitVarSort(const VarSortMap& vmap, VarVec* sortedp) {
     for (VarSortMap::const_iterator it = vmap.begin(); it != vmap.end(); ++it) {
         int size_class = it->first;
         const VarVec& vec = it->second;
-        for (VarVec::const_iterator jt = vec.begin(); jt != vec.end(); ++jt) {
-            const AstVar* varp = *jt;
-            m2v[varp->mtaskIds()][size_class].push_back(varp);
-        }
+        for (const AstVar* varp : vec) { m2v[varp->mtaskIds()][size_class].push_back(varp); }
     }
 
     // Create a TSP sort state for each MTaskIdSet footprint
@@ -2908,8 +2905,7 @@ void EmitCStmts::emitSortedVarList(const VarVec& anons, const VarVec& nonanons,
         }
     }
     // Output nonanons
-    for (VarVec::const_iterator it = nonanons.begin(); it != nonanons.end(); ++it) {
-        const AstVar* varp = *it;
+    for (const AstVar* varp : nonanons) {
         emitVarCmtChg(varp, &curVarCmt);
         emitVarDecl(varp, prefixIfImp);
     }
diff --git a/src/V3EmitCMake.cpp b/src/V3EmitCMake.cpp
index e52f41494..f7f088e3c 100644
--- a/src/V3EmitCMake.cpp
+++ b/src/V3EmitCMake.cpp
@@ -226,9 +226,7 @@ class CMakeEmitter {
                 }
                 *of << " ";
                 const V3StringList& vFiles = v3Global.opt.vFiles();
-                for (V3StringList::const_iterator it = vFiles.begin(); it != vFiles.end(); ++it) {
-                    *of << V3Os::filenameRealPath(*it);
-                }
+                for (const string& i : vFiles) *of << V3Os::filenameRealPath(i);
                 *of << " VERILATOR_ARGS ";
                 *of << "-f " << deslash(hblockp->commandArgsFileName(true))
                     << " -CFLAGS -fPIC"  // hierarchical block will be static, but may be linked
diff --git a/src/V3EmitMk.cpp b/src/V3EmitMk.cpp
index 4b67ba894..f960f50a0 100644
--- a/src/V3EmitMk.cpp
+++ b/src/V3EmitMk.cpp
@@ -193,17 +193,13 @@ public:
         of.puts("VM_USER_CFLAGS = \\\n");
         if (!v3Global.opt.protectLib().empty()) of.puts("\t-fPIC \\\n");
         const V3StringList& cFlags = v3Global.opt.cFlags();
-        for (V3StringList::const_iterator it = cFlags.begin(); it != cFlags.end(); ++it) {
-            of.puts("\t" + *it + " \\\n");
-        }
+        for (const string& i : cFlags) of.puts("\t" + i + " \\\n");
         of.puts("\n");
 
         of.puts("# User LDLIBS (from -LDFLAGS on Verilator command line)\n");
         of.puts("VM_USER_LDLIBS = \\\n");
         const V3StringList& ldLibs = v3Global.opt.ldLibs();
-        for (V3StringList::const_iterator it = ldLibs.begin(); it != ldLibs.end(); ++it) {
-            of.puts("\t" + *it + " \\\n");
-        }
+        for (const string& i : ldLibs) of.puts("\t" + i + " \\\n");
         of.puts("\n");
 
         V3StringSet dirs;
@@ -236,8 +232,7 @@ public:
             of.puts("\n### Executable rules... (from --exe)\n");
             of.puts("VPATH += $(VM_USER_DIR)\n");
             of.puts("\n");
-            for (V3StringSet::const_iterator it = cppFiles.begin(); it != cppFiles.end(); ++it) {
-                string cppfile = *it;
+            for (const string& cppfile : cppFiles) {
                 string basename = V3Os::filenameNonExt(cppfile);
                 // NOLINTNEXTLINE(performance-inefficient-string-concatenation)
                 of.puts(basename + ".o: " + cppfile + "\n");
@@ -292,22 +287,17 @@ class EmitMkHierVerilation {
         of.puts("VM_HIER_VERILATOR := " + perl_wrapper + "\n");
         of.puts("VM_HIER_INPUT_FILES := \\\n");
         const V3StringList& vFiles = v3Global.opt.vFiles();
-        for (V3StringList::const_iterator it = vFiles.begin(); it != vFiles.end(); ++it) {
-            of.puts("\t" + V3Os::filenameRealPath(*it) + " \\\n");
-        }
+        for (const string& i : vFiles) of.puts("\t" + V3Os::filenameRealPath(i) + " \\\n");
         of.puts("\n");
         const V3StringSet& libraryFiles = v3Global.opt.libraryFiles();
         of.puts("VM_HIER_VERILOG_LIBS := \\\n");
-        for (V3StringSet::const_iterator it = libraryFiles.begin(); it != libraryFiles.end();
-             ++it) {
-            of.puts("\t" + V3Os::filenameRealPath(*it) + " \\\n");
+        for (const string& i : libraryFiles) {
+            of.puts("\t" + V3Os::filenameRealPath(i) + " \\\n");
         }
         of.puts("\n");
     }
     void emitOpts(V3OutMkFile& of, const V3StringList& opts) const {
-        for (V3StringList::const_iterator it = opts.begin(); it != opts.end(); ++it) {
-            of.puts("\t\t" + *it + " \\\n");
-        }
+        for (const string& i : opts) { of.puts("\t\t" + i + " \\\n"); }
     }
     void emitLaunchVerilator(V3OutMkFile& of, const string& argsFile) const {
         of.puts("\t@$(MAKE) -C $(VM_HIER_RUN_DIR) -f " + m_makefile
diff --git a/src/V3EmitV.cpp b/src/V3EmitV.cpp
index c2b0f505f..f4702998f 100644
--- a/src/V3EmitV.cpp
+++ b/src/V3EmitV.cpp
@@ -421,16 +421,16 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
         //      %k      Potential line break
         bool inPct = false;
         putbs("");
-        for (string::const_iterator pos = format.begin(); pos != format.end(); ++pos) {
-            if (pos[0] == '%') {
+        for (const char c : format) {
+            if (c == '%') {
                 inPct = true;
             } else if (!inPct) {  // Normal text
                 string s;
-                s += pos[0];
+                s += c;
                 puts(s);
             } else {  // Format character
                 inPct = false;
-                switch (*pos) {
+                switch (c) {
                 case '%': puts("%"); break;
                 case 'f': putfs(nodep, ""); break;
                 case 'k': putbs(""); break;
@@ -459,7 +459,7 @@ class EmitVBaseVisitor : public EmitCBaseVisitor {
                     iterateAndNextNull(nodep->dtypep());
                     break;
                 }
-                default: nodep->v3fatalSrc("Unknown emitVerilog format code: %" << pos[0]); break;
+                default: nodep->v3fatalSrc("Unknown emitVerilog format code: %" << c); break;
                 }
             }
         }
diff --git a/src/V3File.cpp b/src/V3File.cpp
index b3df18c1a..646c9ba75 100644
--- a/src/V3File.cpp
+++ b/src/V3File.cpp
@@ -828,14 +828,12 @@ void V3OutFormatter::putsQuoted(const string& strg) {
     // Don't use to quote a filename for #include - #include doesn't \ escape.
     putcNoTracking('"');
     string quoted = quoteNameControls(strg);
-    for (string::const_iterator cp = quoted.begin(); cp != quoted.end(); ++cp) {
-        putcNoTracking(*cp);
-    }
+    for (const char c : quoted) putcNoTracking(c);
     putcNoTracking('"');
 }
 void V3OutFormatter::putsNoTracking(const string& strg) {
     // Don't track {}'s, probably because it's a $display format string
-    for (string::const_iterator cp = strg.begin(); cp != strg.end(); ++cp) putcNoTracking(*cp);
+    for (const char c : strg) putcNoTracking(c);
 }
 
 void V3OutFormatter::putcNoTracking(char chr) {
@@ -864,43 +862,43 @@ string V3OutFormatter::quoteNameControls(const string& namein, V3OutFormatter::L
     string out;
     if (lang == LA_XML) {
         // Encode chars into XML string
-        for (string::const_iterator pos = namein.begin(); pos != namein.end(); ++pos) {
-            if (pos[0] == '"') {
+        for (const char c : namein) {
+            if (c == '"') {
                 out += string("&quot;");
-            } else if (pos[0] == '\'') {
+            } else if (c == '\'') {
                 out += string("&apos;");
-            } else if (pos[0] == '<') {
+            } else if (c == '<') {
                 out += string("&lt;");
-            } else if (pos[0] == '>') {
+            } else if (c == '>') {
                 out += string("&gt;");
-            } else if (pos[0] == '&') {
+            } else if (c == '&') {
                 out += string("&amp;");
-            } else if (isprint(pos[0])) {
-                out += pos[0];
+            } else if (isprint(c)) {
+                out += c;
             } else {
                 char decimal[10];
-                sprintf(decimal, "&#%u;", (unsigned char)pos[0]);
+                sprintf(decimal, "&#%u;", (unsigned char)c);
                 out += decimal;
             }
         }
     } else {
         // Encode control chars into C style escapes
-        for (string::const_iterator pos = namein.begin(); pos != namein.end(); ++pos) {
-            if (pos[0] == '\\' || pos[0] == '"') {
-                out += string("\\") + pos[0];
-            } else if (pos[0] == '\n') {
+        for (const char c : namein) {
+            if (c == '\\' || c == '"') {
+                out += string("\\") + c;
+            } else if (c == '\n') {
                 out += "\\n";
-            } else if (pos[0] == '\r') {
+            } else if (c == '\r') {
                 out += "\\r";
-            } else if (pos[0] == '\t') {
+            } else if (c == '\t') {
                 out += "\\t";
-            } else if (isprint(pos[0])) {
-                out += pos[0];
+            } else if (isprint(c)) {
+                out += c;
             } else {
                 // This will also cover \a etc
                 // Can't use %03o as messes up when signed
                 char octal[10];
-                sprintf(octal, "\\%o%o%o", (pos[0] >> 6) & 3, (pos[0] >> 3) & 7, pos[0] & 7);
+                sprintf(octal, "\\%o%o%o", (c >> 6) & 3, (c >> 3) & 7, c & 7);
                 out += octal;
             }
         }
@@ -937,9 +935,7 @@ V3OutFile::~V3OutFile() {
 
 void V3OutFile::putsForceIncs() {
     const V3StringList& forceIncs = v3Global.opt.forceIncs();
-    for (V3StringList::const_iterator it = forceIncs.begin(); it != forceIncs.end(); ++it) {
-        puts("#include \"" + *it + "\"\n");
-    }
+    for (const string& i : forceIncs) { puts("#include \"" + i + "\"\n"); }
 }
 
 void V3OutCFile::putsGuard() {
diff --git a/src/V3Global.cpp b/src/V3Global.cpp
index 7faf26c5d..914ac440b 100644
--- a/src/V3Global.cpp
+++ b/src/V3Global.cpp
@@ -52,8 +52,7 @@ void V3Global::readFiles() {
     V3Parse parser(v3Global.rootp(), &filter, &parseSyms);
     // Read top module
     const V3StringList& vFiles = v3Global.opt.vFiles();
-    for (V3StringList::const_iterator it = vFiles.begin(); it != vFiles.end(); ++it) {
-        string filename = *it;
+    for (const string& filename : vFiles) {
         parser.parseFile(new FileLine(FileLine::commandLineFilename()), filename, false,
                          "Cannot find file containing module: ");
     }
@@ -62,8 +61,7 @@ void V3Global::readFiles() {
     // To be compatible with other simulators,
     // this needs to be done after the top file is read
     const V3StringSet& libraryFiles = v3Global.opt.libraryFiles();
-    for (V3StringSet::const_iterator it = libraryFiles.begin(); it != libraryFiles.end(); ++it) {
-        string filename = *it;
+    for (const string& filename : libraryFiles) {
         parser.parseFile(new FileLine(FileLine::commandLineFilename()), filename, true,
                          "Cannot find file containing library module: ");
     }
diff --git a/src/V3GraphAlg.cpp b/src/V3GraphAlg.cpp
index 560f475df..504c719cf 100644
--- a/src/V3GraphAlg.cpp
+++ b/src/V3GraphAlg.cpp
@@ -505,10 +505,7 @@ void V3Graph::sortEdges() {
         // We know the vector contains all of the edges that were
         // there originally (didn't delete or add)
         vertexp->outUnlink();
-        for (std::vector<V3GraphEdge*>::const_iterator it = edges.begin(); it != edges.end();
-             ++it) {
-            (*it)->outPushBack();
-        }
+        for (V3GraphEdge* edgep : edges) edgep->outPushBack();
         // Prep for next
         edges.clear();
     }
diff --git a/src/V3GraphDfa.cpp b/src/V3GraphDfa.cpp
index 40fcaadee..9d2eeb203 100644
--- a/src/V3GraphDfa.cpp
+++ b/src/V3GraphDfa.cpp
@@ -133,11 +133,7 @@ private:
     uint32_t hashDfaOrigins(const DfaStates& nfasWithInput) {
         // Find the NFA states this dfa came from,
         uint32_t hash = 0;
-        for (DfaStates::const_iterator nfaIt = nfasWithInput.begin(); nfaIt != nfasWithInput.end();
-             ++nfaIt) {
-            DfaVertex* nfaStatep = *nfaIt;
-            hash ^= hashVertex(nfaStatep);
-        }
+        for (DfaVertex* nfaStatep : nfasWithInput) hash ^= hashVertex(nfaStatep);
         return hash;
     }
 
@@ -147,9 +143,7 @@ private:
         nextStep();
         // Mark all input vertexes
         int num1s = 0;
-        for (DfaStates::const_iterator nfaIt = nfasWithInput.begin(); nfaIt != nfasWithInput.end();
-             ++nfaIt) {
-            DfaVertex* nfaStatep = *nfaIt;
+        for (DfaVertex* nfaStatep : nfasWithInput) {
             nfaStatep->user(m_step);
             num1s++;
         }
diff --git a/src/V3HierBlock.cpp b/src/V3HierBlock.cpp
index 39435e078..571fdeaf7 100644
--- a/src/V3HierBlock.cpp
+++ b/src/V3HierBlock.cpp
@@ -91,14 +91,10 @@ static string V3HierCommandArgsFileName(const string& prefix, bool forCMake) {
 static void V3HierWriteCommonInputs(std::ostream* of, bool forCMake) {
     if (!forCMake) {
         const V3StringList& vFiles = v3Global.opt.vFiles();
-        for (V3StringList::const_iterator it = vFiles.begin(); it != vFiles.end(); ++it) {
-            *of << *it << "\n";
-        }
+        for (const string& i : vFiles) *of << i << "\n";
     }
     const V3StringSet& libraryFiles = v3Global.opt.libraryFiles();
-    for (V3StringSet::const_iterator it = libraryFiles.begin(); it != libraryFiles.end(); ++it) {
-        *of << "-v " << *it << "\n";
-    }
+    for (const string& i : libraryFiles) *of << "-v " << i << "\n";
 }
 
 //######################################################################
@@ -211,9 +207,7 @@ void V3HierBlock::writeCommandArgsFile(bool forCMake) const {
     *of << "-Mdir " << v3Global.opt.makeDir() << "/" << hierPrefix() << " \n";
     V3HierWriteCommonInputs(of.get(), forCMake);
     const V3StringList& commandOpts = commandArgs(false);
-    for (V3StringList::const_iterator it = commandOpts.begin(); it != commandOpts.end(); ++it) {
-        *of << (*it) << "\n";
-    }
+    for (const string& opt : commandOpts) *of << opt << "\n";
     *of << hierBlockArgs().front() << "\n";
     for (HierBlockSet::const_iterator child = m_children.begin(); child != m_children.end();
          ++child) {
@@ -262,9 +256,7 @@ class HierBlockUsageCollectVisitor : public AstNVisitor {
 
         if (nodep->hierBlock()) {
             m_planp->add(nodep, m_gparams);
-            for (ModuleSet::const_iterator it = m_referred.begin(); it != m_referred.end(); ++it) {
-                m_planp->registerUsage(nodep, *it);
-            }
+            for (const AstModule* modp : m_referred) m_planp->registerUsage(nodep, modp);
             m_hierBlockp = prevHierBlockp;
             m_referred = prevReferred;
         }
@@ -406,9 +398,7 @@ void V3HierBlockPlan::writeCommandArgsFiles(bool forCMake) const {
     V3HierWriteCommonInputs(of.get(), forCMake);
     if (!forCMake) {
         const V3StringSet& cppFiles = v3Global.opt.cppFiles();
-        for (V3StringSet::const_iterator it = cppFiles.begin(); it != cppFiles.end(); ++it) {
-            *of << *it << "\n";
-        }
+        for (const string& i : cppFiles) *of << i << "\n";
         *of << "--top-module " << v3Global.rootp()->topModulep()->name() << "\n";
         *of << "--prefix " << v3Global.opt.prefix() << "\n";
         *of << "-Mdir " << v3Global.opt.makeDir() << "\n";
diff --git a/src/V3LinkLevel.cpp b/src/V3LinkLevel.cpp
index 410e87229..8b6a7d7e7 100644
--- a/src/V3LinkLevel.cpp
+++ b/src/V3LinkLevel.cpp
@@ -61,8 +61,7 @@ void V3LinkLevel::modSortByLevel() {
                                        << "... Suggest see manual; fix the duplicates, or use "
                                           "--top-module to select top."
                                        << V3Error::warnContextNone());
-            for (ModVec::const_iterator it = tops.begin(); it != tops.end(); ++it) {
-                AstNode* alsop = *it;
+            for (AstNode* alsop : tops) {
                 std::cout << secp->warnMore() << "... Top module " << alsop->prettyNameQ() << endl
                           << alsop->warnContextSecondary();
             }
@@ -74,17 +73,13 @@ void V3LinkLevel::modSortByLevel() {
     // Reorder the netlist's modules to have modules in level sorted order
     stable_sort(mods.begin(), mods.end(), CmpLevel());  // Sort the vector
     UINFO(9, "modSortByLevel() sorted\n");  // Comment required for gcc4.6.3 / bug666
-    for (ModVec::const_iterator it = mods.begin(); it != mods.end(); ++it) {
-        AstNodeModule* nodep = *it;
+    for (AstNodeModule* nodep : mods) {
         nodep->clearIter();  // Because we didn't iterate to find the node
         // pointers, may have a stale m_iterp() needing cleanup
         nodep->unlinkFrBack();
     }
     UASSERT_OBJ(!v3Global.rootp()->modulesp(), v3Global.rootp(), "Unlink didn't work");
-    for (ModVec::const_iterator it = mods.begin(); it != mods.end(); ++it) {
-        AstNodeModule* nodep = *it;
-        v3Global.rootp()->addModulep(nodep);
-    }
+    for (AstNodeModule* nodep : mods) v3Global.rootp()->addModulep(nodep);
     UINFO(9, "modSortByLevel() done\n");  // Comment required for gcc4.6.3 / bug666
     V3Global::dumpCheckGlobalTree("cells", false, v3Global.opt.dumpTreeLevel(__FILE__) >= 3);
 }
@@ -105,8 +100,7 @@ void V3LinkLevel::timescaling(const ModVec& mods) {
     if (unit.isNone()) unit = VTimescale(VTimescale::TS_DEFAULT);
     v3Global.rootp()->timeunit(unit);
 
-    for (ModVec::const_iterator it = mods.begin(); it != mods.end(); ++it) {
-        AstNodeModule* nodep = *it;
+    for (AstNodeModule* nodep : mods) {
         if (nodep->timeunit().isNone()) {
             if (modTimedp && !VN_IS(nodep, Iface)
                 && !(VN_IS(nodep, Package) && VN_CAST(nodep, Package)->isDollarUnit())) {
diff --git a/src/V3LinkResolve.cpp b/src/V3LinkResolve.cpp
index f6db3f3f6..b5ad3db70 100644
--- a/src/V3LinkResolve.cpp
+++ b/src/V3LinkResolve.cpp
@@ -304,8 +304,7 @@ private:
         bool inPct = false;
         bool inIgnore = false;
         string fmt;
-        for (string::const_iterator it = format.begin(); it != format.end(); ++it) {
-            char ch = *it;
+        for (const char ch : format) {
             if (!inPct && ch == '%') {
                 inPct = true;
                 inIgnore = false;
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index ab01ce3ca..109c788cb 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -385,10 +385,9 @@ void V3Options::addArg(const string& arg) { m_impp->m_allArgs.push_back(arg); }
 
 string V3Options::allArgsString() const {
     string out;
-    for (std::list<string>::const_iterator it = m_impp->m_allArgs.begin();
-         it != m_impp->m_allArgs.end(); ++it) {
+    for (const string& i : m_impp->m_allArgs) {
         if (out != "") out += " ";
-        out += *it;
+        out += i;
     }
     return out;
 }
@@ -1706,9 +1705,7 @@ void V3Options::parseOptsFile(FileLine* fl, const string& filename, bool rel) {
     // Convert to argv style arg list and parse them
     std::vector<char*> argv;
     argv.reserve(args.size() + 1);
-    for (std::vector<std::string>::const_iterator it = args.begin(); it != args.end(); ++it) {
-        argv.push_back(const_cast<char*>(it->c_str()));
-    }
+    for (const string& i : args) argv.push_back(const_cast<char*>(i.c_str()));
     argv.push_back(nullptr);  // argv is nullptr-terminated
     parseOptsList(fl, optdir, static_cast<int>(argv.size() - 1), argv.data());
 }
diff --git a/src/V3Split.cpp b/src/V3Split.cpp
index 7828f66fd..96f04b1e6 100644
--- a/src/V3Split.cpp
+++ b/src/V3Split.cpp
@@ -782,15 +782,11 @@ protected:
 
         iterateAndNextNull(nodep->ifsp());
 
-        for (ColorSet::const_iterator color = colors.begin(); color != colors.end(); ++color) {
-            m_addAfter[*color] = clones[*color]->elsesp();
-        }
+        for (const auto& color : colors) m_addAfter[color] = clones[color]->elsesp();
 
         iterateAndNextNull(nodep->elsesp());
 
-        for (ColorSet::const_iterator color = colors.begin(); color != colors.end(); ++color) {
-            m_addAfter[*color] = clones[*color];
-        }
+        for (const auto& color : colors) m_addAfter[color] = clones[color];
     }
 
 private:
@@ -803,8 +799,7 @@ class RemovePlaceholdersVisitor : public AstNVisitor {
 public:
     explicit RemovePlaceholdersVisitor(AstNode* nodep) {
         iterate(nodep);
-        for (NodeSet::const_iterator it = m_removeSet.begin(); it != m_removeSet.end(); ++it) {
-            AstNode* np = *it;
+        for (AstNode* np : m_removeSet) {
             np->unlinkFrBack();  // Without next
             VL_DO_DANGLING(np->deleteTree(), np);
         }
diff --git a/src/V3StatsReport.cpp b/src/V3StatsReport.cpp
index d16f8df40..fcbe55dd7 100644
--- a/src/V3StatsReport.cpp
+++ b/src/V3StatsReport.cpp
@@ -135,12 +135,10 @@ class StatsReport {
 
         // Header
         os << "  Stat     " << std::left << std::setw(maxWidth - 5 - 2) << "";
-        for (Stages::const_iterator it = stages.begin(); it != stages.end(); ++it) {
-            os << "  " << std::left << std::setw(9) << *it;
-        }
+        for (const string& i : stages) os << "  " << std::left << std::setw(9) << i;
         os << endl;
         os << "  -------- " << std::left << std::setw(maxWidth - 5 - 2) << "";
-        for (Stages::const_iterator it = stages.begin(); it != stages.end(); ++it) {
+        for (auto it = stages.begin(); it != stages.end(); ++it) {
             os << "  " << std::left << std::setw(9) << "-------";
         }
         // os<<endl;
diff --git a/src/V3String.cpp b/src/V3String.cpp
index b9595c712..12db74f7c 100644
--- a/src/V3String.cpp
+++ b/src/V3String.cpp
@@ -86,9 +86,9 @@ string VString::upcase(const string& str) {
 
 string VString::quoteAny(const string& str, char tgt, char esc) {
     string out;
-    for (string::const_iterator pos = str.begin(); pos != str.end(); ++pos) {
-        if (*pos == tgt) out += esc;
-        out += *pos;
+    for (const char c : str) {
+        if (c == tgt) out += esc;
+        out += c;
     }
     return out;
 }
@@ -100,9 +100,9 @@ string VString::quoteStringLiteralForShell(const string& str) {
     result.push_back(dquote);  // Start quoted string
     result.push_back(escape);
     result.push_back(dquote);  // "
-    for (string::const_iterator it = str.begin(); it != str.end(); ++it) {
-        if (*it == dquote || *it == escape) { result.push_back(escape); }
-        result.push_back(*it);
+    for (const char c : str) {
+        if (c == dquote || c == escape) result.push_back(escape);
+        result.push_back(c);
     }
     result.push_back(escape);
     result.push_back(dquote);  // "
@@ -112,9 +112,9 @@ string VString::quoteStringLiteralForShell(const string& str) {
 
 string VString::spaceUnprintable(const string& str) {
     string out;
-    for (string::const_iterator pos = str.begin(); pos != str.end(); ++pos) {
-        if (isprint(*pos)) {
-            out += *pos;
+    for (const char c : str) {
+        if (isprint(c)) {
+            out += c;
         } else {
             out += ' ';
         }
@@ -125,15 +125,15 @@ string VString::spaceUnprintable(const string& str) {
 string VString::removeWhitespace(const string& str) {
     string out;
     out.reserve(str.size());
-    for (string::const_iterator pos = str.begin(); pos != str.end(); ++pos) {
-        if (!isspace(*pos)) out += *pos;
+    for (const char c : str) {
+        if (!isspace(c)) out += c;
     }
     return out;
 }
 
 bool VString::isWhitespace(const string& str) {
-    for (string::const_iterator pos = str.begin(); pos != str.end(); ++pos) {
-        if (!isspace(*pos)) return false;
+    for (const char c : str) {
+        if (!isspace(c)) return false;
     }
     return true;
 }
@@ -452,8 +452,7 @@ string VSpellCheck::bestCandidateInfo(const string& goal, EditDistance& distance
     string bestCandidate;
     size_t gLen = goal.length();
     distancer = LENGTH_LIMIT * 10;
-    for (Candidates::const_iterator it = m_candidates.begin(); it != m_candidates.end(); ++it) {
-        const string candidate = *it;
+    for (const string& candidate : m_candidates) {
         size_t cLen = candidate.length();
 
         // Min distance must be inserting/deleting to make lengths match
diff --git a/src/V3TSP.cpp b/src/V3TSP.cpp
index 4b7bd469f..6625acf91 100644
--- a/src/V3TSP.cpp
+++ b/src/V3TSP.cpp
@@ -652,9 +652,7 @@ void V3TSP::selfTestString() {
     expect.push_back("3");
 
     if (VL_UNCOVERABLE(expect != result)) {
-        for (std::vector<string>::const_iterator it = result.begin(); it != result.end(); ++it) {
-            cout << *it << " ";
-        }
+        for (const string& i : result) cout << i << " ";
         cout << endl;
         v3fatalSrc("TSP string self-test fail. Result (above) did not match expectation.");
     }
diff --git a/src/V3Waiver.cpp b/src/V3Waiver.cpp
index aedb42391..6cfa87687 100644
--- a/src/V3Waiver.cpp
+++ b/src/V3Waiver.cpp
@@ -47,10 +47,7 @@ void V3Waiver::write(const std::string& filename) {
 
     if (s_waiverList.size() == 0) { *ofp << "// No waivers needed - great!" << endl; }
 
-    for (V3Waiver::WaiverList::const_iterator it = s_waiverList.begin(); it != s_waiverList.end();
-         ++it) {
-        *ofp << "// " << *it << std::endl << endl;
-    }
+    for (const auto& i : s_waiverList) *ofp << "// " << i << std::endl << endl;
 }
 
 V3Waiver::WaiverList V3Waiver::s_waiverList;
diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index 70d8197be..9083cb1af 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -3234,8 +3234,7 @@ private:
         AstNode* argp = nodep->exprsp();
         string txt = nodep->text();
         string fmt;
-        for (string::const_iterator it = txt.begin(); it != txt.end(); ++it) {
-            char ch = *it;
+        for (char ch : txt) {
             if (!inPct && ch == '%') {
                 inPct = true;
                 fmt = ch;
diff --git a/src/Verilator.cpp b/src/Verilator.cpp
index 6244acecb..570f29ff1 100644
--- a/src/Verilator.cpp
+++ b/src/Verilator.cpp
@@ -636,10 +636,8 @@ static string buildMakeCmd(const string& makefile, const string& target) {
     } else if (jobs > 1) {
         cmd << " -j " << jobs;
     }
-    for (V3StringList::const_iterator it = makeFlags.begin(); it != makeFlags.end(); ++it) {
-        cmd << ' ' << *it;
-    }
-    if (!target.empty()) { cmd << ' ' << target; }
+    for (const string& flag : makeFlags) cmd << ' ' << flag;
+    if (!target.empty()) cmd << ' ' << target;
 
     return cmd.str();
 }