段错误 - 核心转储

Question

这里是我的代码：

#include <iostream> 
#include <string> 
#include <algorithm> 

using namespace std; 

string checkpalindrome(string sentence){ 
    sentence.erase(std::remove(sentence.begin(), sentence.end(), ' '), sentence.end()); 

    int unsigned i = 0; 
    for (i = 0; i < sentence.length(); i++){ 
     sentence[i] = tolower(sentence[i]); 
    } 

    if (sentence == string(sentence.rbegin(), sentence.rend())){ 
     cout << sentence << " is a palindrome." << endl; 
    } 
    if(sentence != string(sentence.rbegin(), sentence.rend())){ 
     cout << sentence << " isn't a palindrome." << endl; 
    } 
    return 0; 
} 

int main(){ 
    int x = 1; 
    string originalsentence; 
    while (x == 1){ 
     int input; 
     string sentence; 
     cout << "Press 1 to reverse a string, 2 to check a palindrome, and anything else to quit: "; 
     cin >> input; 

     if(input == 1){ 
      cout << "Enter a sentence to reverse: "; 
      cin.ignore(256, '\n'); 
      getline(cin,originalsentence); 
      sentence = originalsentence; 
      cout << string(sentence.rbegin(), sentence.rend()) << endl; 
     } 

     if(input == 2) { 
      cout << "Enter a sentence to check: "; 
      cin.ignore(256, '\n'); 
      getline(cin,originalsentence); 
      sentence = originalsentence; 
      checkpalindrome(sentence); 
     } 

     cout << "Hit 1 if you want to continue, anything else to quit: "; 
     cin >> x; 
    } 
} 

程序完成，并做一切它应该做的，当我做选项2，检查是否有回文，在最后，它总是除核心转储。我试过包括cin.ignore的，但他们没有帮助。有任何想法吗？

编辑1：所以我改变了g ++抛出的三个警告。他们分别是palindrome.cpp:19: warning: comparison between signed and unsigned integer expressions palindrome.cpp:29: warning: no return statement in function returning non-void palindrome.cpp:35: warning: unused variable âaâ

我把int i改为无符号，在28返回0，并删除了a。现在，当我编译它没有给出任何错误，但是当我运行它时仍然会在完成回文检查时崩溃，并出现此错误。 terminate called after throwing an instance of 'std::logic_error' what(): basic_string::_S_construct NULL not valid Abort (core dumped) 还有什么想法？

Answer 1

从问题复制：

固定！我所需要做的只是return sentence，现在它没有错误地出现