Fix remaining CppCheck warnings and style violations

- Replace obsolete alloca() with std::string and std::vector for safer memory management
- Add explicit keyword to single-argument constructors to prevent implicit conversions
- Improve code safety and consistency across C++ codebase

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jbachorik

ddprof-lib/src/main/cpp/dictionary.h

@@ -63,7 +63,7 @@ class Dictionary {
 
 public:
   Dictionary() : Dictionary(0) {}
-  Dictionary(int id) : _id(id) {
+  explicit Dictionary(int id) : _id(id) {
     _table = (DictTable *)calloc(1, sizeof(DictTable));
     Counters::set(DICTIONARY_PAGES, 1, id);
     Counters::set(DICTIONARY_BYTES, sizeof(DictTable), id);

ddprof-lib/src/main/cpp/flightRecorder.cpp

@@ -1612,8 +1612,8 @@ void FlightRecorder::recordLog(LogLevel level, const char *message,
 
   if (len > MAX_STRING_LENGTH)
     len = MAX_STRING_LENGTH;
-  // cppcheck-suppress obsoleteFunctions
-  Buffer *buf = (Buffer *)alloca(len + 40);
+  std::vector<char> buf_storage(len + 40);
+  Buffer *buf = reinterpret_cast<Buffer *>(buf_storage.data());
   buf->reset();
 
   int start = buf->skip(5);

ddprof-lib/src/main/cpp/jfrMetadata.h

@@ -117,7 +117,7 @@ class Element {
   std::vector<Attribute> _attributes;
   std::vector<const Element *> _children;
 
-  Element(const char *name) : _name(getId(name)), _attributes(), _children() {}
+  explicit Element(const char *name) : _name(getId(name)), _attributes(), _children() {}
 
   Element &attribute(const char *key, const char *value) {
     _attributes.push_back(Attribute(getId(key), getId(value)));
@@ -153,7 +153,7 @@ class Element {
 
 class NoField : public Element {
 public:
-  NoField(const char *name) : Element(name) {}
+  explicit NoField(const char *name) : Element(name) {}
 
   virtual const bool is_nofield() { return true; }
 };

ddprof-lib/src/main/cpp/reservoirSampler.h

@@ -32,7 +32,7 @@ class ReservoirSampler {
     std::vector<T> _reservoir;
 
 public:
-    ReservoirSampler(const int size) :
+    explicit ReservoirSampler(const int size) :
         _size(size),
         _generator([]() {
             std::random_device rd;

ddprof-lib/src/main/cpp/symbols_linux.cpp

@@ -710,10 +710,10 @@ UnloadProtection::UnloadProtection(const CodeCache *cc) {
     // dlopen() can reopen previously loaded libraries even if the underlying file has been deleted
     const char* stripped_name = cc->name();
     size_t name_len = strlen(stripped_name);
+    std::string name_buf;
     if (name_len > 10 && strcmp(stripped_name + name_len - 10, " (deleted)") == 0) {
-        char* buf = (char*) alloca(name_len - 9);
-        *stpncpy(buf, stripped_name, name_len - 10) = 0;
-        stripped_name = buf;
+        name_buf.assign(stripped_name, name_len - 10);
+        stripped_name = name_buf.c_str();
     }
 
     // Protect library from unloading while parsing in-memory ELF program headers.

ddprof-lib/src/main/cpp/symbols_linux.h

@@ -11,7 +11,7 @@ class SymbolDesc {
   const char *_desc;
 
 public:
-  SymbolDesc(const char *s) {
+  explicit SymbolDesc(const char *s) {
     _addr = s;
     _desc = strchr(_addr, ' ');
   }
@@ -32,7 +32,7 @@ class MemoryMapDesc {
   const char *_file;
 
 public:
-  MemoryMapDesc(const char *s) {
+  explicit MemoryMapDesc(const char *s) {
     _addr = s;
     _end = strchr(_addr, '-') + 1;
     _perm = strchr(_end, ' ') + 1;

ddprof-lib/src/main/cpp/unwindStats.h

@@ -160,7 +160,7 @@ class ExclusiveLock {
  private:
   SpinLock &_lock;
  public:
-  ExclusiveLock(SpinLock &lock) : _lock(lock) {
+  explicit ExclusiveLock(SpinLock &lock) : _lock(lock) {
     _lock.lock();
   }
   ~ExclusiveLock() {
@@ -175,7 +175,7 @@ class SharedLock {
  private:
   SpinLock &_lock;
  public:
-  SharedLock(SpinLock &lock) : _lock(lock) {
+  explicit SharedLock(SpinLock &lock) : _lock(lock) {
     _lock.lockShared();
   }
   ~SharedLock() {