IF语句导致分段错误？

Question

我遇到了一个相当混乱的问题.看起来我程序中的IF语句导致了分段错误.

我正在使用外部库,并在IF语句中调用外部库中的代码,因此我无法提供这些函数的完整代码,因为我也没有.

会发生什么的基本例子.所以这个例子引起了我的兴趣Segmentation fault.

IRank *rank;

//Generating wavelet tree from BWT with sdsl library
    if(true) {
        std::cout << "I am in IF" << endl; // this gets printed on the screen
        wt_huff<> wt;                      // right after that - segm fault
        construct_im(wt, BWT, 1);
        WTRank wtrank(&wt);
        rank = &wtrank;
    }

但是,同样的例子,但没有IF,当我评论它时,不会导致Segmentation fault并正常执行.

IRank *rank;

//Generating wavelet tree from BWT with sdsl library
//if(true) {
    std::cout << "I am in IF" << endl; // again this gets printed
    wt_huff<> wt;                      // no segmentation error this time
    construct_im(wt, BWT, 1);
    WTRank wtrank(&wt);
    rank = &wtrank;
//}

原始示例:

//    // Decide what rank function to use
    IRank *rank;
    if(m_wt) {
        // Multiary Wavelet Tree rank function :: student implementation
        mwt::node *m_wtree = mwt::generateMultiaryWT(BWT, ary);
        MultiWTRank m_wt_rank(m_wtree, ary);
        rank = &m_wt_rank;
    } else if(b_wt) {
        // Binary Wavelet Tree rank function :: SDSL implementation
        wt_huff<> b_wtree;
        construct_im(b_wtree, BWT, 1);
        WTRank b_wt_rank(&b_wtree);
        rank = &b_wt_rank;
    } else if(non_wt) {
        // Implementation of rank function not using Wavelet Tree
        LinRank lin_rank(BWT);
        rank = &lin_rank;
    } else {
        // should not happen
    }

//...
run(rank);

这里发生了什么,它是如此令人困惑？

编辑:从此片段调用其他代码的示例

    #include "IRank.h"
#include "mwt.h"


class MultiWTRank : public IRank {

private:
    mwt::node *wt;
    int n_ary;

public:
    MultiWTRank(mwt::node *root, int ary) {
        wt = root;
        n_ary = ary;
    }

    ~MultiWTRank() {
    }

    index_type rank(index_type index, symbol_type symbol);
};

所以这是在第一个IF中构建的.

EDIT2:提供一个代码,生成一个指向树的指针,可能会导致问题

class mwt {
public:
    // Structure of a MW tree node
    typedef struct node {
        vector<int> data;
        vector<node*> next;
    } node;

    // ...



    static node* generateMultiaryWT(string input, int ary) {

        //...

        return root;
    }

节点创建如下:

   static node* InitRoot(int ary){
        node *root = new node;
        for(int iter = 0; iter < ary; iter++){
            root->next.push_back(NULL);
        }
        return root;
    }

Answer 1

在if之前声明'wt'和'wtrank'变量.如果在if之后的块内声明它,则其范围仅限于该块.在它超出范围并且'rank'指针变为悬空之后,因此稍后访问它可能会导致段错误.