Integer copy constructor incorrectly handles negative values

[yebing115]

Issue: Integer copy constructor incorrectly handles negative values

Description

When copying a PList::Integer object that contains a negative value, the copied object incorrectly represents the value as a large positive integer instead of preserving the original negative value.

Steps to Reproduce

#include <plist/plist++.h>
#include <string>

std::string to_xml(plist_t node) {
  std::string ret;

  char* s = nullptr;
  uint32_t len = 0;
  if (plist_to_xml(node, &s, &len) != PLIST_ERR_SUCCESS) {
    return ret;
  }

  ret.append(s, len);

  plist_mem_free(s);

  return ret;
}

int main() {
  int64_t v = -1;
  PList::Integer i1(v);
  PList::Integer i2(i1);  // Copy constructor

  printf("i1 xml:\n%s\n", to_xml(i1.GetPlist()).c_str());
  printf("i2 xml:\n%s\n", to_xml(i2.GetPlist()).c_str());

  return 0;
}

Compile and run:

clang++ -std=c++11 -lplist++-2.0 -lplist-2.0  test.cpp -o test
./test

Expected Behavior

Both i1 and i2 should produce the same XML representation:

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">
<plist version=\"1.0\">
<integer>-1</integer>
</plist>

Actual Behavior

i1 produces the correct XML, but i2 (the copy) produces:

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">
<plist version=\"1.0\">
<integer>18446744073709551615</integer>
</plist>

This happens because 18446744073709551615 is the unsigned representation of -1 in a 64-bit two's complement integer.

Root Cause

In the copy constructor for PList::Integer, the code was using plist_set_uint_val with GetValue(), which converts the negative signed integer to an unsigned integer, causing the value to wrap around to a large positive number.

Fix

The fix replaces the problematic code in the copy constructor with a proper node copy:

// Before (problematic):
plist_set_uint_val(_node, i.GetValue());

// After (fixed):
plist_free(_node);
_node = plist_copy(i.GetPlist());

This ensures that all attributes of the original node, including its sign, are properly preserved in the copy.