Remove bogus gcc-8.1 warning (#3870)

Summary:
Various rearrangements of the cch maths failed or replacing = '\0' with
memset failed to convince the compiler it was nul terminated. So took
the perverse option of changing strncpy to strcpy.

Return null if memory couldn't be allocated.

util/status.cc: In static member function ‘static const char* rocksdb::Status::CopyState(const char*)’:
util/status.cc:28:15: error: ‘char* strncpy(char*, const char*, size_t)’ output truncated before terminating nul copying as many bytes from a string as its length [-Werror=stringop-truncation]
   std::strncpy(result, state, cch - 1);
   ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
util/status.cc:19:18: note: length computed here
       std::strlen(state) + 1; // +1 for the null terminator
       ~~~~~~~~~~~^~~~~~~
cc1plus: all warnings being treated as errors
make: *** [Makefile:645: shared-objects/util/status.o] Error 1

closes #2705
Closes https://github.com/facebook/rocksdb/pull/3870

Differential Revision: D8594114

Pulled By: anand1976

fbshipit-source-id: ab20f3a456a711e4d29144ebe630e4fe3c99ec25

include/rocksdb/status.h

@@ -26,7 +26,7 @@ class Status {
  public:
   // Create a success status.
   Status() : code_(kOk), subcode_(kNone), state_(nullptr) {}
-  ~Status() { delete[] state_; }
+  ~Status() { free((void *) state_); }
 
   // Copy the specified status.
   Status(const Status& s);
@@ -284,7 +284,7 @@ inline Status& Status::operator=(const Status& s) {
   if (this != &s) {
     code_ = s.code_;
     subcode_ = s.subcode_;
-    delete[] state_;
+    free((void *) state_);
     state_ = (s.state_ == nullptr) ? nullptr : CopyState(s.state_);
   }
   return *this;
@@ -308,7 +308,7 @@ inline Status& Status::operator=(Status&& s)
     s.code_ = kOk;
     subcode_ = std::move(s.subcode_);
     s.subcode_ = kNone;
-    delete[] state_;
+    free((void *)state_);
     state_ = nullptr;
     std::swap(state_, s.state_);
   }

util/status.cc

@@ -10,24 +10,17 @@
 #include "rocksdb/status.h"
 #include <stdio.h>
 #include <cstring>
+#include <string.h>
 #include "port/port.h"
 
 namespace rocksdb {
 
 const char* Status::CopyState(const char* state) {
-  const size_t cch =
-      std::strlen(state) + 1; // +1 for the null terminator
-  char* const result =
-      new char[cch];
-  result[cch - 1] = '\0';
 #ifdef OS_WIN
-  errno_t ret;
-  ret = strncpy_s(result, cch, state, cch - 1);
-  assert(ret == 0);
+  return _strdup(state);
 #else
-  std::strncpy(result, state, cch - 1);
+  return strdup(state);
 #endif
-  return result;
 }
 
 Status::Status(Code _code, SubCode _subcode, const Slice& msg, const Slice& msg2)
@@ -37,7 +30,7 @@ Status::Status(Code _code, SubCode _subcode, const Slice& msg, const Slice& msg2
   const size_t len1 = msg.size();
   const size_t len2 = msg2.size();
   const size_t size = len1 + (len2 ? (2 + len2) : 0);
-  char* const result = new char[size + 1];  // +1 for null terminator
+  char* const result = (char*) malloc(size + 1);  // +1 for null terminator
   memcpy(result, msg.data(), len1);
   if (len2) {
     result[len1] = ':';