va_arg 导致 std::bad_alloc

Question

每当我运行我的程序时，我都会抛出 std::bad_alloc 异常，这会导致中止发生。 std::bad_alloc 只有在调用 va_arg 时才会被抛出。奇怪的是崩溃的代码是由讲师提供的。我没有写崩溃的行。 Valgrind 告诉我这是由 new/new[] 引起的。为什么 va_arg 会造成这种情况？ bad_alloc 仅在执行时出现（在其他地方也是如此）。

void Library::addKeywordsForItem(const Item* const item, int nKeywords, ...)
 {
     // the code in this function demonstrates how to handle a vararg in C++

     va_list         keywords;
     string          keyword = "test";
     bool            successFlag = false;
     sArray          keywordV;
     cout << "Before lookupItem\n";
     Item*           item2 = lookupItem(item);
     cout << "After lookupItem\n";

     va_start(keywords, nKeywords);
     cout << "after va_start\n";
     for (int i = 0; i < nKeywords; i++) //this code adds the items to a map of set to create a fast access structure for keyword searches
     {
         cout << "before keyword assign\n";
         keyword = va_arg(keywords, string); //Crash here
         cout << "after keyword assign\n";
         // do something with each keyword
         cout << "before HERE\n";
         keywordV.push_back(keyword); //pushes keyword onto vector
         cout << "HERE\n";
         successFlag = addToSMap(item, keyword, keywordDbase); //This function is literally a copy/paste of the code
         //originally designed for this function
     }
     va_end(keywords);

     //Sets in keywords
     item2->setKeywords(keywordV);

     if(!successFlag) //Should never execute
         cout << "This code reeks verily of wrongness.\n";
 }

上面的代码是调用下面讲师写的代码行

library->addKeywordsForItem(item, 2, "autism", "Asperger's Syndrome");

这是我得到的错误

Valgrind

**5851**    new/new[] failed and should throw an exception, but Valgrind
**5851**    cannot throw exceptions and so is aborting instead.  Sorry.
==5851==    at 0x4C275AC: ??? (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==5851==    by 0x4C27DC6: operator new(unsigned long) (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==5851==    by 0x4F57496: std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_assign(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) (basic_string.tcc:265)
==5851==    by 0x4F577E8: std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator=(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) (basic_string.h:1181)
==5851==    by 0x4085F8: Library::addKeywordsForItem(Item const*, int, ...) (Library.cpp:79)
==5851==    by 0x401BB5: main (Asgmt04.cpp:38)

计划

terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc Aborted

讲师设计了使用 va_args 的循环（我只是填写了它的作用）所以我不确定他的代码为什么会导致崩溃。我的代码会导致崩溃吗？有人可以提供一些见解吗？

Answer 1

"autism" 和 "Asperger's Syndrome" 是 const char * 值，而不是 string 值，因此尝试将它们读取为 strings 会导致未定义的行为。

va_arg 导致 std::bad_alloc

va_arg causes std::bad_alloc

c++

variadic-functions

bad-alloc

c++11