我的代码可以编译、执行，但对于某些输入会崩溃

My code compiles, executes, but crashes for certain inputs

本文关键字：于某些 输入 崩溃 执行 代码 编译 我的      更新时间：2023-10-16

我试图获得两个字符串的最长公共子序列的长度。它适用于大多数输入，但对于指定的输入会崩溃。代码如下:

#include <cmath>
#include <string>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
/* Utility function to get max of 2 integers */
int max(int a, int b)
{
    return (a > b)? a : b;
}
/* Returns length of LCS for X[0..m-1], Y[0..n-1] */
int lcs(string &X, string &Y, int m, int n )
{
    int L[5000 + 1][5000 + 1] = {0};
    int i, j;
    /* Following steps build L[m+1][n+1] in bottom up fashion. Note 
      that L[i][j] contains length of LCS of X[0..i-1] and Y[0..j-1] */
    for (i = 0; i <= m; i++)
    {
        for (j = 0; j <= n; j++)
        {
            if (i == 0 || j == 0)
                L[i][j] = 0;
            else if (X.at(i - 1) == Y.at(j - 1))
                L[i][j] = L[i - 1][j - 1] + 1;
            else
                L[i][j] = max(L[i - 1][j], L[i][j - 1]);
        }
    }
    /* L[m][n] contains length of LCS for X[0..n-1] and Y[0..m-1] */
    return L[m][n];
}
int main() {
    string A, B;
    cin >> A;
    cin >> B;
    int count1 = lcs(A, B, A.size(), B.size());
    cout << count1;
    return 0;
}

，输入字符串如下:

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

我尝试使用c风格的字符串，但它正在崩溃。如果输入字符串大于阈值，我也尝试将其分成多个字符串，但仍然不起作用。希望有人能发现这个bug。

这个局部声明:

    int L[5000 + 1][5000 + 1] = {0};

在调用堆栈上分配了2500万个int -s，即4字节字(所以100兆字节)。在当前的台式机和笔记本电脑上，典型的调用堆栈最多有几兆字节，所以你最好在每个调用帧中使用几千字节(但是YMMV)。

你肯定会遇到堆栈溢出。

您可以考虑堆分配的c++标准容器，例如std::vector(即使您在堆栈上有本地容器变量，大多数实际数据也是堆分配的)。

正如我所评论的，是时候学习更多的调试工具了:g++ -Wall -Wextra -g，也许还有-fsanitize=address, gdb调试器，valgrind, strace。细节是特定于实现的。

当然，阅读几本关于c++ 11(或c++ 14)的好书:编程- c++

的原理和实践

如果你在Linux上编程，《高级Linux编程》也值得一读。

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