【发布时间】：2017-02-13 13:35:57
【问题描述】：
我在尝试编译 C++ 程序时遇到分段错误问题，但不确定问题出在哪里。我怀疑问题出在 .find() ..... 可能是迭代器运算符
以下是test01.cpp的一部分，我在其中运行它来测试代码并使用打印语句找出问题所在：
bool confirmEverythingMatches(const btree<long>& testContainer, const set<long>& stableContainer) {
cout << "Confirms the btree and the set "
"contain exactly the same values..." << endl;
for (long i = kMinInteger; i <= kMaxInteger; i++) {
cout << "Start of for-loop to find iterator for comparisons..." << endl;
if (stableContainer.find(i) != stableContainer.end()) {
cout << "can find i (" << i << ") in stableContainer!" << endl;
} else {
cout << "cannot find i (" << i << ") in stableContainer!" << endl;
}
cout << "In between finding i in stable and testContainers..." << endl;
if (testContainer.find(i) != testContainer.end()) {
cout << "can find i (" << i << ") in testContainer!" << endl;
} else {
cout << "cannot find i (" << i << ") in testContainer!" << endl;
}
cout << "Before assigning the find to boolean variables..." << endl;
bool foundInTree = (testContainer.find(i) != testContainer.end());
cout << "testContainer.find(i) != testContainer.end()" << endl;
bool foundInSet = (stableContainer.find(i) != stableContainer.end());
cout << "stableContainer.find(i) != stableContainer.end()" << endl;
if (foundInTree != foundInSet) {
cout << "- btree and set don't contain the same data!" << endl;
cout << "Mismatch at element: " << i << endl;
return false;
} else {cout << "foundInTree == foundInSet!!!" << i << endl;}
}
cout << "- btree checks out just fine." << endl;
return true;
}
} // namespace close
/**
* Codes for testing various bits and pieces. Most of the code is commented out
* you should uncomment it as appropriate.
**/
int main(void) {
// initialise random number generator with 'random' seed
initRandom();
cout << "after initRandom().." << endl;
// insert lots of random numbers and compare with a known correct container
btree<long> testContainer(99);
cout << "after specifying max node elements in testContainer.." << endl;
set<long> stableContainer;
cout << "after constructing stableContainer.." << endl;
insertRandomNumbers(testContainer, stableContainer, 1000000);
cout << "after inserting random numbers into testContainer and for success inserts, also into stableContainer.." << endl;
btree<long> btcpy = testContainer;
cout << "after copy assigning a copy of testContainer to btcopy.." << endl;
confirmEverythingMatches(btcpy, stableContainer);
cout << "after confirming everything internally matches between testContainer and stableContainer.." << endl;
return 0;
}
我在运行程序时得到的输出（编译时没问题）是这样的：
Confirms the btree and the set contain exactly the same values...
Start of for-loop to find iterator for comparisons...
cannot find i (1000000) in stableContainer!
In between finding i in stable and testContainers...
ASAN:DEADLYSIGNAL
=================================================================
==7345==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000018 (pc 0x000108d132a8 bp 0x000000000000 sp 0x7fff56eee6f0 T0)
#0 0x108d132a7 in btree<long>::find(long const&) const (test01+0x1000022a7)
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (test01+0x1000022a7) in btree<long>::find(long const&) const
==7345==ABORTING
Abort trap: 6
当我尝试在另一台机器上运行它时，我也遇到了这个错误：
==29936==ERROR: AddressSanitizer failed to allocate 0x200000 (2097152) bytes of SizeClassAllocator32: 12
发现进入find()的时候会出现segmentation fault：
/**
* Identical in functionality to the non-const version of find,
* save the fact that what's pointed to by the returned iterator
* is deemed as const and immutable.
*
* @param elem the client element we are trying to match.
* @return an iterator to the matching element, or whatever the
* const end() returns if no such match was ever found.
*/
template<typename T> typename btree<T>::const_iterator
btree<T>::find(const T& elem) const {
std::cout << "CONST ITERATOR'S FIND" << std::endl;
Node *tmp_ = root_;
std::cout << "1" << std::endl;
while(true) {
std::cout << "2" << std::endl;
size_t i;
std::cout << "3" << std::endl;
// go through all elements from root to tail
for (i = 0; i < tmp_->__occupied_size_; ++i) {
std::cout << "4" << std::endl;
if (tmp_->__elem_[i] == elem) {
std::cout << "5" << std::endl;
// find the elem, return an iterator
return const_iterator(tmp_, i, this);
std::cout << "6" << std::endl;
} else if (tmp_->__elem_[i] > elem) {
std::cout << "7" << std::endl;
// elem is not in current Node, go to descendants
// for the elem.
if (tmp_->__descendants_ == nullptr) {
std::cout << "8" << std::endl;
return cend();
std::cout << "9" << std::endl;
} else {
std::cout << "10" << std::endl;
tmp_ = tmp_->__descendants_[i];
std::cout << "11" << std::endl;
break;
}
}
}
// handling boundaries cases
if (i == tmp_->__occupied_size_) {
std::cout << "12" << std::endl;
if (tmp_->__descendants_[i] == nullptr) {
std::cout << "13" << std::endl;
return cend();
std::cout << "14" << std::endl;
} else {
std::cout << "15" << std::endl;
tmp_ = tmp_->__descendants_[i];
}
}
}
}
这个查找的打印语句是：
CONST ITERATOR'S FIND
1
2
3
4
4
7
10
11
2
3
4
7
10
11
ASAN:DEADLYSIGNAL
【问题讨论】：
-
这个问题的代码太多了，你能不能试着把它剪成minimal reproducible example。
-
请将您的问题edit 提供给minimal reproducible example。包含的链接提供了有关如何执行此操作的帮助。
-
剪掉了
-
您尝试了多少调试？打印出来并没有多大帮助，但调试会显示程序和数据的状态，这对于找出问题更有用。
-
0x000000000018看起来您正试图在btree::find中使用空指针。使用调试器找出确切的位置。
标签： c++ iterator segmentation-fault find b-tree